Radio Boulevard
Western Historic Radio Museum

Vintage Longwave Receivers - Part 2

10.  Profiling the Signal Corps BC-314-D

11.  Profiling the USN-National Co. RBL-5

12.  Profiling the USN RBA Receivers

CFT-46154 and CFT-46300

Includes Rebuilding Information and reception log for RBA-1 SN:972
Description and performance for RBA-6 SN:181
Photos of RBA-1 with Field Mod installed, Photos of RBA-2 SN:168

13A/B.   Profiling 2 Mackay Radio & Telegraph Co. Receivers
RC-123 Coast Guard Receiver  SN: 97 - 1942
 Type 3001-A Marine Radio Receiver SN: 52-M-070 - 1952


photo: Shipboard Radio Room in the late-twenties to early thirties - note the vacuum tube transmitter in the right corner of the operator's desk.



U.S. Army Signal Corps

Farnsworth Television & Radio Corp.



BC-344-D - LF/MW Radio Receiver - 1944

150kc  to  1500kc


SN: 5     Contractor: CFN (Farnsworth) 


Order No. 10651-PHILA-44


The BC-344 belongs to a family of radio receivers that were designed by the U.S. Army Signal Corps at Fort Monmouth, New Jersey in the late-thirties. The early versions of the receiver used more aluminum in the chassis and some early versions were painted with a "leatherette" finish paint (properly called "Crackle Finish.") By the time WWII contractor manufacturing had started, the receiver used an all-steel chassis and the paint used was the standard black wrinkle finish. Farnsworth Television & Radio Corporation built the AC operated versions, those being the BC-342 and the BC-344. RCA Manufacturing Co., Inc. built the DC operated versions, those being the BC-312 and BC-314. The BC-312 and BC-342 are shortwave receivers with six frequency ranges that cover 1.5mc up to 18.0mc. The BC-314 and BC-344 are LF (low frequency) and MW (medium wave) receivers with four frequency ranges the cover 150kc up to 1500kc. The BC-344 has two RF amplifiers and two IF amplifiers (four 6K7 tubes.) A separate Mixer (6L7) and LO (6C5) are used. The BFO uses a 6C5 triode, the detector-AVC-first AF is a 6R7 and the AF Output tube is a 6F6. There are ten tubes used in the BC-344 including the 5W4 rectifier tube used in the RA-20 power pack that mounts internally. No selectivity filter is used in the BC-344. Audio output is generally 4000Z ohms but may be set to 250Z ohms by moving a jumper inside later versions of the receiver. The LS-3 loudspeaker was commonly used with the BC-344 receiver although a headset would allow copy of weaker signals.

photo above: Army communications set-up for local ground transmissions. The telephone box allowed interfacing a telephone contact through the BC-191 transmitter. Note that the vernier dial locks are removed from all three receivers.

The Signal Corps utilized the BC-312/314/342/344 receivers in many applications. Fixed stations generally used two or more receivers paired with at least one BC-191 transmitter. A typical Army station is shown in the photo to the left. Note that three BC-342 receivers are utilized with an AC operated BC-191 transmitter (the RA-34 power supply is barely visible under the transmitter table.) Mobile stations ranged from small vehicle set-ups to the SCR-299 that used a BC-342 and BC-344 set up with a BC-610 transmitter, all powered by an AC generator towed in a trailer. Most DC set-ups operated on 12vdc from vehicle battery-charger systems. There was a 28vdc BC-312 version, the BC-312-NX.

BC-344-N on Long Wave? - I've been interested in how well the BC-344 would perform on MW and LF reception for some time. I have a "rough-condition" receiver that had been painted "metallic" green. I even had it on the workbench once but I lost interest when I saw some "hamster" rework inside. Recently (2016,) I obtained another BC-344 receiver that happened to have the scarce shock mount installed. This receiver seemed to be pretty original and virtually complete. Replacements for the few missing or poor condition parts were easily located in my BC-312/314/342/344 junk box.

Reworking the BC-344-D - Since the BC-312/314/342/344 were essentially "workhorses" for the Army, many are in rough condition today. All will require some work and many require a full restoration in order to function correctly. The receiver is difficult to disassemble and this has saved many BC-344s (and 342s) from being modified too much by hams. Most hams preferred to modify the easy-to-work-on BC-348-Q. Most 344/342 receivers will be very close in alignment because all of the adjustments were "locked" if they were easy to access, like the IF transformers, or hidden by covers or plugs in the case of the RF adjustments. Most receivers will be missing the dial lock since this piece often times interfered with the rotation of the vernier knob. It's not unusual to do mostly a cosmetic restoration and have the receiver work with all original parts with the exception of the dual electrolytic filter capacitor located in the RA-20 power pack.

Front Panel Dismounting - One of the common problems with any of this series of receivers was present on this BC-344. That is, the plastic dial index that always seems to have warped, cracked, shrunken in size and discolored to the point where it's no longer covers the dial itself or is even transparent. Luckily, I had an excellent condition replacement. Unfortunately, to install the index requires completely dismounting the front panel.

I say "unfortunately" because this task is unbelievably complicated by the Army's mechanical design that never seemed to even consider the possibility that the receiver might need to be disassembled someday. Besides the abnormal amount of front accessed screws there are three screws that mount from the backside of the panel that must be removed. The two fuse holders must be unsoldered and removed. All of the phone jacks and controls must have their mounting nuts removed. The wires to the dial lamps have to be unsoldered. All of the wires going to the front panel "trunk" connector have to be unsoldered. The power input terminal strip has to be dismounted. All screw connections to Antenna and Ground connections have to be dismounted. Knobs and control nuts must be removed. At this point, you'd think the front panel would easily come off, but not yet! The Fast Tuning gear has a pinned shaft that is flanged. You can't remove the front panel unless the gear and shaft are taken apart and that requires driving out the pin. However, once the gear and flanged shaft are apart, the front panel finally can be dismounted.

photo right: A rear view of the chassis showing the stout construction of these receivers

At this point, installing the replacement dial index is easy (it's mounted with eight screws!) Since the front panel is off, now is the time for a thorough cleaning and touch-up. I use jet black nitrocellulose lacquer that is thinned about 3:1 for touch-ups. After the lacquer has set for a while, I rub down the panel with light weight machine oil. Usually, this will blend the color of the touch-ups with the original black wrinkle paint making the touch-ups invisible.

When remounting the front panel, it will be noted that all of the 6-32 screws are the same length. However, there are three different length 4-40 screws. The four long 4-40s are for the wire mounts. There are two short 4-40s and the rest are all the same length. The two short 4-40s are very important. There are two places where, if long 4-40 screws are used, they will protrude far enough thru the rear panel mounted nut to contact the dial mask with possible scratching of the mask when the band switch is operated. The "short" 4-40 screws must be mounted as follows: One "short" screws is by the band change switch and is the screw nearest the "G" in "CHANGE" in the nomenclature of that switch. The other "short" 4-40 is used near the lower left side of the data plate (the screw head almost is contacting the data plate edge.)

The other observation is the small component board that is mounted to the back of the front panel uses two different length stand-offs. The reason is that the lower screw must past thru a part of the chassis mounting flange and the top screw doesn't. The longer stand-off is the upper one.

Patience is required in any BC-321,314,342,344 rework. The work is tedious and none of the component parts are easy to access without removing another part or assembly first.

  Electrolytic Filter Capacitor - Most military gear used oil-filled paper dielectric capacitors as the filters. The disadvantage of this type of capacitor was its large size but the advantage was long-term reliability. Since space was at a premium in the RA-20 power supply, a dual electrolytic filter capacitor was used. The advantage was a small size for two 8uf 450vdc caps but the disadvantage now is, after 75 years, the dielectric paste has dried up and drastically reduced the value of the capacitor.

There's ample room to mount new electrolytic capacitors inside the old capacitor can. There are many methods to accomplish this "re-stuffing." I cut the cap in two and remove the old cap and black wax using a heat gun to soften the wax. This allows the old capacitor to be easily pulled out of the can. I install new capacitors connecting them to the correct terminals and then epoxy the can back together. I remount the rebuilt cap and connect it into the circuit.

The photo to the left shows the underside of the BC-344 and in particular the RA-20 power pack. Note that the RA-20 is "swung out" on the right side hinge mount. Also note the wiring harness that is connected to the power terminal strip. 

Miscellaneous Rework - Sometimes the OFF-MVC-AVC switch contacts don't allow the operator the ability to turn the receiver on. These are special build, stacked switches that have the MVC and AVC switches enclosed. Luckily, the AC on/off switch is only covered with a fiber disk that can be bent to allow access to the arm and contacts. It's usually only dirt or maybe minor corrosion that is causing the problem. This can be cleaned off using a small piece of Alu-Ox paper or a very small wire brush. It might be necessary to bend the arm slightly to have better contact. If the AC contacts are damaged beyond reconditioning then the entire switch has to be replaced with a used-good original. These are sometimes difficult to find except from parts sets. The same switch is used on all of the versions of the BC-312, 314, 342 and 344. Alignment Notes - IF is 92.5kc. Note in the photo above left that the large LO box (far left) has four plugs that are covering access to the trimmers for each band. Also note the shield cover over the two RF amp boxes and the Mixer box that is preventing easy access to these trimmers. Each IF transformer adjustment has a lock nut on the threaded shaft to prevent tampering (see photo above right showing top of chassis.) Other than the lower frequencies involved, the BC-344 is straight forward in its alignment procedure.
Performance on a Wire Antenna -  The antenna used was my 135' CF Inv'd Vee with 96' of ladder line with the two feed line wires tied together. This is something like a "T" antenna and it performs fairly well on LF. The test listening was on January 29, 2018 from 1915 to 1945 PST. I only tuned the BC-344-D from 405kc down to 300kc. Within the frequency span and time period I tuned in 25 NDBs. Greatest USA DX was IN 353kc in International Falls, MN. Greatest DX was YMW 366kc in Manawaki, Quebec, CANADA. Another Canadian NDB tuned was YXL 346kc in Sioux Lookout, Ontario. Listening QTH was Dayton in Western Nevada.

All signals were heard over a headset, not by loudspeaker. BFO was on and stations generally tuned for zero beat of carrier to then hear the MCW tone correctly. Sometimes it's advantageous to tune the BFO about 400hz to 1000hz from the IF frequency. This will enhance the 400hz on some weak NDB stations. The AVC was off. Noise level wasn't too bad and I'd rate the conditions as "very good."

The BC-344-D is a capable LW receiver that has ample sensitivity in the medium wave portion of the spectrum using a wire antenna. There is no crystal filter or any other method to reduce IF bandwidth so many signals are "heard" over what seems to be a fairly wide IF passband. It's easy to select one particular signal and then concentrate on that tone or sound of the signal to then successfully copy the call. Most of the time this process will be with very, very weak signals that are within the passband with stronger signals. If the received noise seems to be covering up some weaker signals it's possible to slightly "detune" the antenna trim (ALIGN INPUT control) to reduce the noise while not affecting signal copy.

While the BC-344-D is kind of a "basic" superhet with no fancy filters or output limiters, it does a good job with the few controls provided. It's certainly sensitive enough and the reduction of the VERNIER tuning mechanism allows for easy tuning of all stations, including NDBs. Without an output limiter though there isn't any way to reduce "pops and clicks" or heavy static. Wearing the 'phones just ahead of the ears is recommended. I'm sure if the BC-344-D was used with a wire antenna in a modern RFI-noisy, urban-type location the weak signal DX reception would be terrible. But, in the rural RFI-quite area here in Dayton, NV, the BC-344-D does a very good job of pulling in NDB DX using just a wire antenna.

Performance on  a Tuned Loop Antenna - The remotely tuned loop is six feet "point to point" of its diamond-shape and tuned using varactor diodes with a variable bias voltage source. The receiver is connected to a pick-up loop that is mounted within the main loop. Test listening was on February 1, 2018 from 1930 to 2000 PST. I only tuned the BC-344 from 325kc up to about 390kc. 23 NDB stations were tuned in during that time. Conditions were very good. Greatest USA DX was FIS 332kc in Key West, FL. Greatest Canadian DX was GW 371kc in Jarpik, Kuujjuarapik, Quebec, CAN.

All signals were heard over a headset, not by loudspeaker. BFO was on, AVC was off. Loop Antenna was pointing NE/SW for the entire test listening period.

The BC-344-D running with the tuned loop antenna is a surprisingly good performer. Without any bandwidth controls, one would expect noise to be a problem but the loop does keep the noise level somewhat lower than the wire antenna. Additionally, the "loop tuning" provided the ability to slightly detune the peak adjustment which lowered the noise without causing loss of the signal. This was a nice advantage for signals that were "in the noise." Also, the ALIGN INPUT (antenna trimmer) could be used to slightly detune the antenna and reduce the noise peaks allowing some weaker signals to be copied. These two features, loop tuning and antenna trimmer, do a lot to make up for the "wide open" IF bandwidth which does have a tendency to be somewhat noisy.

As mentioned in the "wire antenna test" section, the BC-344-D is a pretty basic receiver with no filters or no bandwidth control. Yet, I was still able to copy NDBs all the way to the east coast and Canadian NDBs out to Quebec. I don't think any vintage LW receiver enthusiasts will be going out to purchase a BC-344-D to use as their main LW receiver, but I was impressed with its performance and would rate the receiver as one of the better medium wave and low frequency receivers. It is fully capable of receiving DX LW signals and, with its incredible "WWII Military" appearance, makes a fine addition to any collection of vintage LW receivers. Additionally, if you get tired of listening to MCW signals on 'phones, you can always tune in almost the entire AM BC band and listen on an LS-3 loudspeaker - very cool.





National Co., Inc.


   RBL-5, CNA-46161-B  - MW, LF & VLF Radio Receiver - 1945

15kc to 600kc


National Company also provided a great LW receiver for the Navy in WWII - the RBL series of regenerative receivers. Following the long Navy tradition of  National providing NC-100A types of receivers - like the RAOs and similar HF receivers, the RBL series uses the same general appearance with a similar dial layout and a familiar band switching feel. Though the bandswitch looks like the RAO catacomb system, it isn't. The mechanism uses several large gears to simultaneously actuate two large ceramic switches to provide band changes. The RBL is the same approximate size as the RAO receivers so it was probably intended that they be paired up for coverage from 15kc to 600kc on the RBLs and 540kc to 30mc on the RAOs. Unlike the earlier LW receivers described above, the RBL has a built in power supply and has direct frequency readout on the illuminated dial. Like the RAO receivers, Wells-Gardner Company was a second contractor and built the RBL-3 and RBL-4 versions under contract using many National parts for assembly (see RBL-3 at the bottom of this write-up.) The RBL-6 receivers were supplied with a one-piece, larger cabinet that had the shock mounts installed on the bottom of the cabinet. The front panel of the RBL-6 receiver was 19" wide however the receiver wasn't intended for rack mounting. Side panels were installed on the chassis and the entire chassis could be easily removed from the cabinet for maintenance.
The circuit uses a cascade of three 6SK7 RF amplifier stages. The detector is a 6SG7 regenerative autodyne detector followed by a 6H6 audio limiter circuit followed by a 6K6G audio tube. The power supply rectifier is a 5U4 in early RBLs but later was changed to a 5Y3G. Like the RAO, some RBL receivers were built by Wells-Gardner Company. Heavy duty construction, ample shielding, copper-plated cabinet under the black wrinkle paint are standard construction used in the RBL receivers. They were normally bolted to a cushioned mount that attached to the holes in the lower front and rear corners of the cabinet. Nowadays these mounts are usually missing. Included in the circuit is an audio filter for wide or narrow bandwidths (switch on left side of escutcheon below ON-OFF switch) and an adjustable audio limiter (switch and control on right side of escutcheon.) The limiter is very well designed and works wonders in reducing the static crashes while not distorting the audio signal. The direct frequency readout on the dial is the major advantage of using the RBL receivers and the accuracy is impressive considering the receiver's age. The illuminated dial is quite a departure from the usual military LF receiver. The lower controls (l to r) are gain, regeneration, bandswitch, antenna trim, oscillation push button and frequency trim.

This RBL-5 was acquired from a ham neighbor here in Virginia City. It required a little work before it was functioning to its specifications. The tubular antenna connection input that attaches to the box that bolts to the back of the cabinet was shorted internally so essentially whatever antenna was connected was shorted to chassis. Removal of the tubular connector and just running the coax through the box directly to the antenna and ground terminals fixed the problem. Also, there was a soldering job at the audio output transformer that was poorly done. Exactly what the object of the solder job was is not known but it probably was in search of the lack of output that was really caused by the shorted antenna input. Fortunately, no original parts were removed and only the connections to the audio output transformer were moved to incorrect terminals. We just returned everything to the original connections and then the receiver output returned to normal.


photo left: The chassis on this RBL-5 is immaculate and all original. RF section is on the right side of the chassis and the power supply, limiter and audio sections are on the left side.


I have logged a lot of NDBs using this RBL-5 receiver, primarily because the RBL-5 is easy to use, very sensitive, has direct frequency readout and the limiter functions quite well. The limiter makes long sessions of receiving comfortable since the static crashes are reduced to the point where they aren't causing headaches anymore. I take the audio output right from the earphone jack on the front panel running 600 ohm 'phones for best copy on weak signals. The NBDs normally copied are multiple stations operating on the same frequency, with two and sometimes three different CW identifications being heard simultaneously. Using the RF trimmer and the Antenna Compensator controls, it is usually possible to enhance one or the other of the MCW signals and identify the particular NDB, (the RAK and RAZ LW receivers also have this ability to manipulate the signal a little to enhance copy.) The RBL works particularly well with the tuned loop antenna and this provides the ability to add some directional characteristics to the reception. Additionally, the loop can be slightly de-tuned to allow enhancing NDBs that are on one side or the other of antenna resonance which can sometimes help with copy.




photo right: The underside of the RBL-5 is also immaculate and all original. The photo shows the multiple gears that drive the two ceramic bandswitches. Construction is first rate as expected from National Company. Note that the alignment trimmers are all clustered together. The bottom cover has a sliding access panel that allows the receiver to be aligned with the bottom cover installed - probably why the RBL-5 has such an accurate dial readout.

Shown in the photos right and left is the Wells-Gardner Co. version, the RBL-3. This receiver is also in excellent condition. Note the difference in the transformers and chokes used in the W-G version compared to the National RBL-5. Typically, W-G used mostly National parts but did use their own transformers, chokes and smaller components. Note the rectifier tube in the upper left corner is a 5U4G rather than the 5Y3GT used in later versions of the RBL.  Performance of the W-G RBL-3 is the same as the National RBL-5.


RCA-Federal Telephone & Radio Corporation



CFT-46154, RBA-1
MW, LF & VLF Table Top Radio Receiver - 1941 contract
SN: 972     Accepted by USN 6-26-1943

CFT-46300, RBA-6
MW, LF & VLF Rack Mount Radio Receiver - 1945 contract
SN: 181   No Acceptance Tag

CFT-46154, RBA-2 SN: 168


15kc to 600kc

1943 RBA-1 CFT-46154

In the late thirties, it was becoming apparent that a replacement receiver was going to be necessary for the aging series of longwave receivers used by the Navy at that time. The receivers included the RAA superhet from 1931, the RAG TRF from 1933, the RAK TRF with regenerative detector from 1935 and the various upgraded versions of these receivers that were built on later contracts. The new LW receiver design was going to blend the advantages of the TRF plus tracking BFO design of the RAG receiver but built with modern circuits. Using a TRF with tracking BFO was advantageous in keeping the leakage radiation on the antenna to a very low level that prevented enemy direction finding equipment from determining the location of the receiver. Additionally, the low-level of radiation allowed the receiver to operate in the presence of other receiving and transmitting equipment along with radar equipment without interference. The tracking BFO design utilized a section of the main tuning condenser so the BFO tuning condenser was ganged to the main tuning. Since the new receiver was not a superheterodyne, the BFO had to track at 1kc above the tuned frequency allowing a 1kc heterodyne to be heard thus allowing CW to be readily copied. There were a couple of very good reasons for not designing the new LF receiver as a superheterodyne. First, was to provide complete coverage of the tuning range of 15kc to 600kc. Most IF amplifier sections utilized around 400kc to 500kc for the intermediate frequency, right in the middle of the most used portion of the medium wave band (as far as the Navy was concerned.) Operation of the IF amplifier at, for example 455kc, would eliminate a section of frequency coverage of about 20kc either side of the intermediate frequency. Some superhet LW receivers moved the IF above the intended tuning range (15kc to 600kc) but there were disadvantages to this solution to the problem. For example, the RBH receiver uses an IF of 1500kc but any transmitting activity around 1500kc will "leak into" the IF section of the receiver and cause heterodynes throughout the tuning ranges.

At $3000 each cost to the Navy, the new RBA receiver was certainly an expensive receiver but a look inside reveals the incredibly high level of electro-mechanical design and construction. The tuning range is from 15kc up to 600kc in four bands. The illuminated dial readout is direct in kilocycles along with a logging scale that uses two scales - one on the main dial and a separate "units" logging scale. The mechanics of the tuning system design allows for super-smooth operation. The Gain adjustment controls the RF stage sensitivity of the receiver but there is also a "tracking" gain control (also called the auxiliary gain control) that is in series with the Gain control but geared to the main tuning. This allowed a variable gain compensation to frequency tuned that provided a constant gain level across the tuning range of each band. To protect the operator's ears, since most operation would be via earphones, an Output Limiter circuit allows an adjustment of the maximum output of the receiver based on the setting of the Output Level control. The O.L. can be switched on or off via a toggle switch on the front panel. The O.L. could be used in high level static conditions or for unexpectedly strong local signals. Two meters are provided, one to monitor Audio Output Level in db and one to monitor the B+ voltage.  Two levels of audio selectivity are provided, Broad selectivity rolls off the audio response at about 1300hz with an internal LP filter and the Sharp position is provided by a 1kc bandpass filter for CW in noisy conditions or in cases of interference. Voice modulated signals sound somewhat "muffled" due to the 1300hz roll off but the only voice signals encountered anymore will be from 530kc up to 600kc (bottom of the standard AM BC band.) Below 530kc, all signals are either data streams, MCW, MSK or other types of coded signals (unless hams are ever allowed to use 600M or 2200M.) The audio output is 600 ohms Z and is intended for earphones although the RBA can drive a matched loud speaker if necessary. The audio Z can be anything from 30 Z ohms up to 600 Z ohms. Negative feedback is utilized in the last two audio stages to reduce level changes as multiple earphones were added to the output (up to 20 sets of 600Z phones could be operated by a single RBA receiver.)

1945 RBA-6, CFT-46300 SN:181 - The RBA-6 came from the factory painted Navy Gray and in a rack mount cabinet.

The separate power supply is the CRV-20130, which is the same power supply used for the 15 tube RBB and RBC superheterodyne receivers. The CRV-20130 provides the filament voltage and B+ requirements via an armored cable with heavy-duty connectors. The power supply will easily operate two RBA receivers for emergency conditions and two separate connectors are provided. The power supply has a cold-cathode regulator tube (OC3) and a HV rectifier (5U4.) The RBA uses eight tubes, three 6SK7 RF amplifiers, one 6J5 Triode Detector, one 6SK7 BFO, two 6SJ7 AF amplifiers and one 6K6 AF Output. Table top versions of the RBA receiver were identified as C(FT)-46154 (FT would indicate that Federal Tele. & Radio Corp. was the contractor) and CFT-46154-A (RBA-5) while the rack mount versions are identified as CFT-46300. Internally, all versions of the RBA receiver circuit are the same.

 photo left: Inside the RBA-6 receiver showing the top of the chassis. All of the TRF coils are in the cylindrical shielded cans to the left. The moveable covers on top of the cans allow access to the trimmers for alignment. The two front coils are for the tracking BFO. Note the gear-driven potentiometer coupled to the main tuning. This is the auxiliary gain control that allows for constant gain across the tuning ranges. Also note the shielded meters. The blue "dots" on the tops of the tubes are my indicators that I have tested these tubes and they are in good operational condition.



 photo right: The underside of the RBA-6 chassis. Full shielding of each RF section is provided when the bottom cover is installed. The heavy-duty band switch uses ceramic mounts with .25" silver-plated contact buttons. All components are mounted on terminal boards or are mounted directly to the chassis. Tracking BFO is the front section of coils. RF3, RF2 and RF1 are next going towards the rear. The rear-most set of coils are the Antenna Input coils.

The RBA-6 shown is from a 1945 contract. This version is identical to the RBA-5 internally but the RBA-6 is a rack mounted configuration only and is painted smooth Navy gray rather than black wrinkle. Judging by the condition of this receiver, it is unlikely that it was ever put into service. It is all original except for the substitution of an SO-239 UHF connector in place of the Navy coax connector for the antenna input. The RBA-6 is an impressive performer with ample sensitivity, direct dial read-out with illumination and a tracking BFO rather than regenerative-autodyne detector. The tracking BFO actually works quite well for finding the carrier on weak NBDs. The dial accuracy is excellent and allows tuning the NDBs by frequency rather than constantly referring to charts or graphs. The LP filter does limit the audio frequency response on BC stations but not to the point where the voice is incomprehensible. The O.L. works quite well at limiting the maximum output (which is usually due to static bursts) while not distorting the signal. The RBA-6 is a first-class longwave receiver capable of receiving any of the signals found below 500kc if used in an RF-quiet area with an appropriate antenna.

RBA-6 Performance - I have been using this RBA-6 during the morning hours for late September through most of October 2009 and have found the receiver to be a phenomenal performer. I can usually separate LLD 353kc in Hawaii from local Reno AP NDB NO 351kc and this is using just a wire antenna and not relying on the directional characteristics of a loop antenna. That's amazing selectivity for a TRF receiver. I've probably tuned in well over 100 NDBs but so far only two were new copies and they were West Coast NDBs. The wire antenna I'm using is the 135' center-fed dipole with 43' of open feed line that is shorted together at the receiver antenna terminals. This antenna, while not really something I designed for LW, seems to work quite well with all of the LW receivers. Radio Rossii 279kc is received every morning coming in very strong - Russian LW station located on Sakhalin Island. JJY also can be received every morning on 40kc coming out of Japan. Noise is the only limitation on reception and for better noise reduction I have to run a loop antenna.

photo above: This USN radio op is listening to the RBA receiver and is ready to copy on the mill. Other equipment is the General Radio LR-1 Frequency Meter, the RBB and RBC receivers. This photo of the U.S.S. Mugford in 1946

January 21,2010 - I finally got the RBA-6 up to the top floor of the house where it can be used with the six-foot loop antenna. I had tried using the loop antenna in the basement but the concrete floor and the rock foundation were a serious detriment to the loop's performance. The top floor of the house is actually about 30 feet above ground level and allows the loop to function quite well even though it is located indoors. The performance of the RBA-6 on the loop is amazing. The signals just jump out of a fairly quite background noise level. Much quieter than running on the wire antenna. Most frequencies seem to have at least three NDBs active and by tuning the loop I can usually enhance one or the other to allow copy. Quite an improvement in performance.

November 7, 2013 - QTH is now Dayton, Nevada and the antenna is a 300 foot long end-fed wire up about 50 feet. This antenna works quite well with the RBA-6 although the noise level is probably higher than using the loop. However, the actual ambient noise level is so low in Dayton that the 300 ft wire seems to provide better signal levels than the loop ever did in Virginia City. More info to come,... Nov. 8, 2013 0615 PST tuned in JJY at 40kc, very loud signal.


RBA-1, CFT-46154 - I had the receiver shown to the left for a short time. It's the early table top version RBA-1, the CFT-46154. This particular RBA-1 has had a common Field Change Modification Contract installed that changes the toggle switches for Reception mode and Output Limiter to knob-type controls. There are additional changes internally. The B+ meter has been replaced on this receiver. Additionally, like many receivers that have gone through a field rebuild, the cabinet is black wrinkle (it is for an RBA-1) while the receiver's panel has been repainted gray. This RBA-1 was traded off in 2015.

RBA-1 CFT-46154 SN: 972  -  Restoration Log

I acquired RBA-1 CFT-46154 SN: 972 (shown to the right) from a fellow in Texas in October 2017. It was shipped to Nevada via UPS. No damage was sustained during transport. I purchased this particular RBA-1 because it was the first all-original, black wrinkle finish, complete example that I had ever come across. Most RBA receivers found around here look like the RBA-1 shown in the photo above. That is, most have the Field Change modifications and have been repainted gray. Not that SN: 972 didn't have problems. For example, the DB meter glass was cracked to several places. The meter, however, worked fine. Band switching from Band 1 to Band 2 was normal. To Band 3 felt rough, like fine gear teeth meshing and switching to Band 4 was stiff but it would switch. All toggle switches seemed to function okay. There was a little bit of dial drag on the logging dial which was slightly rubbing against the housing. Inside was very nice with all shields present. Some very minor corrosion in just a few locations - nothing serious. Even the antenna input was still the original Navy coax fitting. Cosmetically, the cabinet was very scratched up with quite a bit of paint missing, especially on the top. Front panel was very good with some minor blemishes and old touch-ups. The dial mask on Band 4 needs some attention as there are some "pin points" of corrosion present. All knobs were present but the spinner was missing from the tuning knob. The two nomenclature panels were in good condition. All tags were present and in good condition on both the panel and cabinet. The original tuning chart was present with NSS (WWII Radio Central USN, Annapolis, MD,) shown at 18kc.

This RBA-1 didn't come with the CVR-20130 power supply or the armored power cable. Fortunately, I had a spare 20130 and a spare cable to apply power to this receiver. Normally, I wouldn't apply power without a thorough check out first, but the seller told me he had the receiver operating, so there was some confidence that nothing serious was going to happen. I did check all of the tubes first and ended up replacing three. I had SN:972 out in the shop, so I connected my 275 ft CF dipole with the 77 ft of feed line shorted to act as the antenna. Upon power up and warm up, the receiver was receiving KTHO 590kc up a Lake Tahoe quite loud. I had a 600Z ohm modified LS-3 connected to the phone jack on the front panel. Further tuning had MOG 404kc, a NDB from Montegue, CA and FCH 344kc from Fresno, CA coming in strong. This was about 3PM, so no DX NDBs were heard.  However, when switching to Band 3 the output was nil, same for Band 2. Switching to Band 1 the receiver again had output. NAA on 24.0kc was strong but NLK on 24.8kc was extremely strong. NPM on 21.4kc was strong from Lualualei, Hawaii.

So, this RBA-1 is somewhat functional. The most serious problem is the non-operative Band 2 and Band 3, however since the receiver works on Bands 1 and 4, the problem is certainly in the RF stages ahead of the detector. Additionally, repairing the mechanical issues of the band switching "roughness" and logging dial drag will be necessary. The DB meter glass repair will be accomplished by replacing the entire housing - it's a Weston Type 506 and they're common. Finally, when fully functional, a complete alignment. Cosmetics will be necessary too but that looks to mainly consist of cleaning and touch-up.


photo above: RBA-1 SN: 972 "as received" Oct. 11, 2017. Note the bubble-wrapped tubes piled up on the RF coils. Some of the cabinet can be seen to the right. This photo was taken before the power-up test.

Dismounting the Front Panel - This is an arduous task that is not well-described in the manual, at least in the NAVSHIPS 900,708 manual I have. In order to repair the logging dial drag, the rough feeling band switch and restore the dial mask, I had to access the cast metal housing that has the dial, the dial mask and the band switching inside. The only access to into this housing is from the front and the entire front panel has to be dismounted to even see the front of this housing. To get the front panel off I first removed all of the knobs. The ANT. COMP. and INPUT CLPG. control shafts needed to be removed by loosening the set screws at the flexible coupling for each control and withdrawing the shafts out the front panel. All controls that have panel nuts needed the nuts and washers removed. The bottom cover needed to be removed. Then the two chassis-withdrawal knobs needed to be removed. The meter covers needed to be removed so the meter leads could be disconnected. The meters can stay mounted to the panel. The tuning chart frame needed to be taken off. The screws underneath mount a resistor board to the rear of front panel and these screws had to be taken out. The PHONES jack nut has to be removed and the shield around the phone jack itself has to be dismounted by the four screws on the side of the chassis. The dress nuts and the hex nuts that mount the four toggle switches had to be removed. I had to dismount the housing around the logging dial. Underneath there are two set screws that mount the logging dial to the tuning shaft. I loosened the set screws to remove the logging dial. The spacer around the band switch shaft had to be removed. Now came the difficult part,...there were six screws across the front panel that secure the front panel directly to the chassis. These had nylock nuts on the inner chassis side. I had to use a 3/8" open end wrench to hold the nut while the screw was removed. Two nuts are difficult to access because of the harness prevents seeing the nut but it can be done by "feel." The four vertical screws on the left side also had nylock nuts to mount them. On the right side, two screws had nylock nuts and two had pem nuts. The pilot lamp assembly had a 5/8" nut on the back side. When loosened, then the red jewel front could be unscrewed and dismounted. Now the front panel could be removed. Photo right shows the RBA chassis with the panel removed. All removed parts were "bagged and tagged" in small plastic bags. This "bagging" method is extremely helpful to prevent loosing any parts and for easing reassembly.    Oct 16, 2017

Accessing the Dial Mask and Band Switching - With the front panel off, I could see the housing was a two-piece assembly. The front part of the housing was mounted with four screws. The next step is to remove the four screws and lock washers that mount the front cover of the housing. Now the front cover can be removed and this exposes the tuning dial and the band switch arced gear. The dial mask is mounted to the front cover. In addition to the dial mask there is also a gear on the back side of the mask that engages the band switch arced gear and actuates the band changing function. However, since the mask needed to be restored it had to be separated from the front cover. This required removal of the retaining collar that was mounted to the band switch shaft. The set screw wasn't a hex like all the other set screws had been. This set screw was a spline or Bristol-type. Also, just to make removal difficult, the collar was pinned to the shaft. This required driving out the securing pin with a proper size punch. If done correctly with the proper tool, the pin comes right out. The collar has to be placed on a large vise that has the jaws slightly open. With a long thin diameter punch, the pin can be driven out. The set screw was only to keep the collar in place while the pin hole was drilled and the pin driven in. It doesn't have much of a purpose now and was easy to loosen. This allowed the collar to be removed and the dial mask, band switch shaft and drive gear could be separated from the front cover.

Painting the Dial Mask - Once the dial mask was removed its condition seemed a little worse than I thought. The minor flecks of corrosion were numerous but most of them seemed to be around BAND 4. I removed the black paint with stripper and wiped everything down with denatured alcohol. I worked over the surface with steel wool to be sure it was smooth and no blemishes would show when repainted. I used Krylon Flat Black for the paint as the initial coat.

photo right : The dial mask/cover assembly removed exposes the dial and the arced band switch gear.

Restoring the Mask Nomenclature - Of course, painting the dial mask covered up the frequency band nomenclature. These letters and numbers are embossed so they are somewhat higher than the flat surface of the mask. To restore the nomenclature requires carefully removing the paint just from the top surface of the letters and numbers. I had to do the nomenclature recovery in two steps. After the initial paint in flat black, I used a special angled tool (that I made) that could hold a very small piece of 320 grit Al-Ox paper. This was used to carefully remove the paint just from the nomenclature. Of course, there was some slight scuffing and other minor blemishes that happened to the paint surrounding the nomenclature. The next step was to carefully cut masking tape pieces to exactly cover only the nomenclature. It sounds time-consuming but it only takes about 25 minutes to do. Next, I applied a coat of Satin Black, which is much darker black than flat black. When this paint had dried, I removed the masking tape. Now, only very small areas between the letters and numbers had the flat black paint showing. These areas were so small that I touched them up using a "ultra-fine point" Pilot pen with black ink. The entire mask was then wiped down with a clean cotton cloth to even out the paint surface. It sounds like a lot of work and it is fairly time-consuming but the results are worth the effort since the dial mask is quite visible, directly in front of you, on all bands, whenever you're using the receiver.     Oct 19, 2017

Dial Mask and Band Switch Reassembly - I put a small dab of grease on the mask shaft and installed into the front cover of the housing. The washer and collar were then installed onto the shaft and the collar pin installed. The spline set screw was tightened. The band switch was set on Band 2 so the mask was rotated to show Band 2 also. The front cover was carefully placed in position and moved slightly until the gears meshed while the mask remained showing Band 2 centered. The four screws were installed. The adjustment for the gear mesh clearance is accomplished by moving the front cover upwards (reduces mesh) and tightening the screws. Testing switching showed that the mesh was correct as the switching was ultra-smooth and not binding.

photo right: Dial mask after restoration

Front Panel Restoration - This is really just a thorough cleaning with a brass wire brush (suede shoe brush) and Glass Plus to remove all dirt, grime and cigarette residue. The original wrinkle finish is very tough and can take this type of cleaning but you can't be real aggressive. You just want to remove the dirt not the paint. The front panel had been stripped of all tags and the two dial covers. The silver (engraved) nomenclature needed substantial cleaning. The front panel must have been pretty dirty as it took about five cleanings until the paper towels didn't turn gray with dirt and stayed fairly white. After this many cleanings, the nomenclature was very legible now. Next is the touch-up. I've been using jet black nitrocellulose lacquer for the last year or so. This method replicates how the USN did "touch-ups" on equipment that was being repaired but was not in the depot for an echelon-type rebuild. The lacquer looks too dark when being applied but with the final wipe down with 10W machine oil, the jet black matches the original wrinkle paint color quite well. The touched-up front panel is shown to the right.   

DB Meter Repair - The meter glass was broken in this meter. Luckily, it was a Weston Type 506, which are very common meters. The mechanical zero mechanism on a 506 is mounted in the glass making replacement glass difficult, if not impossible. The easiest method is to find a similar 506 meter that has the meter case with mounting flange. It doesn't matter what the meter scale is,...all I wanted was the metal case front with the glass. I dug around in the junk boxes and found a good candidate. The swap of the cases is easy only requiring removal of the three mounting screws on each meter, aligning the meter zero adjuster-pin with the adjustment slot while sliding the new housing glass in place and then reinstalling the screws. The only difference in the meter I used was that the glass was standard while the original USN meter glass had a "non-glare" treatment. Other than that, the transplant was perfect.      Oct 20, 2017

Plastic Used in Logging Dial Window and Tuning Chart Cover - These transparent plastic pieces are made of a celluloid-type of plastic that is very sensitive to water. Just plain old H2O will "fog" the plastic. The more water added, the worse the fogging gets. With enough water, the surface of the plastic will begin to dissolve. The only way to clean the plastic used in the Logging Dial cover and the plastic used for the Tuning Chart cover is to use oil. I used 10W machine oil (3 in 1 oil, actually.) The oil cleaned the plastic surface and didn't cause any change in the transparency. Another note on the Logging Dial window, if this piece is dismounted only leave it dismounted for enough time to clean it and the dial housing. This plastic piece is fairly thick and if not secured by mounting screws it will quickly begin to warp. I noticed the warp starting in about 15 minutes, so I remounted the plastic to allow it to retain its proper shape. Front Panel Remount - I had to touch-up all of the panel mounting screws with black lacquer. Several were missing all of their paint but most just had chips of missing paint. I mounted the two meters after I had touched-up their mounting screws (and washers.) The most difficult part of the front panel remounting is installing the two chassis shims. These two pieces are mounted by the six horizontal chassis screws. I had to have the six screws protruding thru their respective panel holes to hold the two shims in place while I guided the front panel into the proper position to fully seat against the chassis and the side panels. I also had to guide the four toggle switches along with the Gain control and the Output Level control thru their respective panel holes in order for the panel to fully seat. Once the panel is seated all of the other panel screws were installed. All but two of the panel to chassis mounting screws have nylock nuts that complicate the panel installation, especially the six horizontal chassis screws that have four of the nuts difficult to access with a wrench. I first installed the other panel screws and nuts but didn't fully tighten them. They were holding the panel in place but allowed for minor movement. For the six horizontal screws, the easiest method was to have the receiver upside down as this allowed the best view of where the nuts had to go. Once the nuts were installed I still didn't fully tighten the screws yet. I still had to install the screws that mounted the chassis withdrawal knobs. Once I had all of the panel mounting screws and nuts installed and threaded together, then I could go ahead and tightened all of the panel screws.

Each toggle switch had an flat washer, a hex nut and a dress nut for their mounting. The switches and two controls use external star locking washers that are mounted on the back side of the panel and flat washers and hex nuts are used on the front. The phone jack uses a special fiber insulator that has a locating pin that has to be inserted into the mating hole in the back of the panel. The phone jack body front just fits into the recessed channel which keeps the phone jack from turning when the panel nut is tightened. I had to make sure that two fiber washers and one metal dress washer were used when installing the phone jack nut. This was to provide the correct chassis insulation and the proper spacing so the phone jack nut would tighten up.

Reassembly Notes - When I installed the metal spacer for the band switch shaft I had to make sure that the spring washer was mounted on the band switch shaft with the "fingers" facing up so it pressed against the recessed area behind the spacer. This spring provides a thrust load on the band switch shaft. When installing the logging dial, it also had a spring that mounted on the tuning shaft and loaded the logging dial. To synchronize the logging dial, I first had to set the main tuning to the minimum frequency on any band. I noted that the logging scale actually is a little longer than the tuning scales but I had to set the main dial to "0" on its logging scale. I then installed the logging dial on the tuning shaft with the load spring in place. I set the logging dial to read "0" on its scale and pressed the logging dial firmly as far back onto the shaft to load the spring and then tightened the set screws. I installed the logging dial cover and checked the operation for any rubbing or binding while tuning. I also checked that each 100s segments on the main dial's logging scale matched the logging dial at "0" or within a couple of divisions of "0." I then installed the meter covers and then cleaned and installed the knobs.

I was pretty sure that during reassembly, with tightening up the panel screws and the other mounting screws, some paint chips were going to "pop off." I ended up with two fairly large chips and several smaller chips. These were touched up with black lacquer.

With everything back in place, retesting and troubleshooting the Band 2 and Band 3 problems could begin.    Oct 22, 2017

Minor Troubleshooting - Problem one was with the DC Voltmeter reading very low. Pressing on the meter face gently would result in the voltage reading going up to normal, +220vdc. The problem was that I just reinstalled the lug connections and didn't clean them first. Cleaning with a brass wire brush got the terminals and lugs clean and when reassembled, the voltage reading was normal.

Problem two was that the ANT. COMP. control wasn't indicating the air variable position correctly. The ANT. INPUT shield has to be removed (easy to do - only four screws) to see the plates of the condenser. I set the condenser per the manual,...full mesh is 10 to the right side of the scale. There's a rotation limiting pin on the extension shaft thru the front panel that only allows 180 deg. of rotation so the air variable position has to match the panel scale.

On to the serious problems,...

Repairing Split Hex-Collars on Air Variable Trimmer Capacitors - So far, the problems had been minor stuff. I was now going to find out why Band 2 and Band 3 were inoperative. I could hear a few signals on Band 3 but they were very weak. Band 2 was dead. I used a RF Signal Generator to inject a RMS voltage into the Antenna Input to act as a steady, high-level signal. When adjusting the trimmers to resonate the RF coils, the problem became "painfully" obvious,...on Band 2, two of the air variable trimmers had split hex-collars and the trimmer rotor had dropped down and was "shorting" the rotor to stator plates which shorts the RF coil which in turn takes the grid of that RF amplifier tube to ground. I adjusted the rotors until they were fully un-meshed which removes the short circuit but leaves that RF coil "not tuned" and the rotor too low to mesh with the stator. Enough signal leaks thru to tell that these are the defective components keeping Band 2 from operating. I found that Band 3 had one split hex-collar trimmer that was already un-meshed. This was why Band 3 seemed to work but had weak signals. Only Band 1 and Band 4 had all good trimmers.

The repair of these split hex-collar trimmers requires the removal of the defective RF coil assemblies. First remove the shield-can by removing the top nylock nut and the four screws at the base of the shield. Removal of the actual RF coil assembly can be fairly difficult due to the 16 gauge buss wire used for connections. This requires a fairly large soldering iron (or gun, I used a Weller 250W gun.) On most of the buss connections the wire is wrapped a half turn around the terminal. On some wires, the joint can be heated and the buss wire lifted off of the terminal with large needle nose pliers. Other joints may require the use of a small pointed tool (like a small awl) to get the buss wire bend started once the solder was molten. At this point, long needle nose pliers can slightly unwrap the buss wire from the terminal and then it can be lifted off of the terminal. There are four buss wires and two stranded wires per coil assembly that need to be removed. Once desoldered, then the nylock nuts can be taken off and the coil assembly removed. Be careful when doing the reinstallation of the buss wire onto the terminals. If the buss wire was unwrapped too much it may break when bending it back into position. Try to only unbend the buss wire slightly when removing and then no problems should be encountered when reinstalling.

photo above
: The hex-collar on the right is correct and not split. The hex-collar on the left is split and has been taken off to show the trimmer rotor shaft.

photo above:   Cardboard shims are installed between the rotor and stator plates to maintain proper spacing for repair

An ideal hex-collar repair would require access to a machine shop to make a new hex-collar from 1/4" brass hex stock. The shaft on the trimmer condenser is slightly tapered from 0.152" up to 0.154" and this requires that the hex stock have a slight taper also. The height of the collar is also important since the press fitting of the collar will stop when the adjusting slot of the rotor is at the top of the collar. This fit then has to result in the proper spacing of the rotor and stator plates. Original dimension for the height of the hex-collar was ~0.190" and the new collar would also have this same dimension. The final measuring involves having the hole perpendicular to the top and bottom surfaces of the hex-collar to allow even movement of the adjustment without binding.

It's also possible to correctly position the split hex collar on the shaft and then drill and pin the collar to the shaft. The split should be perpendicular to drill hole for highest strength. A very small diameter steel pin will be necessary since the shaft is only about 0.154" in diameter. The pin should be an easy "press fit" since it's only holding the collar in position on the shaft.

Either of these two repair methods are impractical for most restorers because we don't have access to a machine shop. The next repair method described doesn't require any special tools.

An easier repair of the split hex-collar is to use solder to hold the hex-collar in place with the proper spacing for the trimmer plates. Cardboard shim stock installed between the rotor and stator bottom plates will provide a firm stationary spacing for the plates. A minimum of four shims should be used for best support of the rotor plates. I used .022" thick cardboard that can be salvaged from small boxes or the cardboard backing from tablets or from many other sources. As long as the shim thickness is about .022" the plate spacing will be correct.

The first step is to remove the RF coil assembly from the receiver. I've tried to do this repair with the coil assembly in place (just the shield-can removed) and it is almost impossible to get the cardboard shims installed. There's just not enough space for access and there's limited visibility, making the whole operation impossible. Although it's difficult to unsolder the 16 gauge buss wiring to remove the RF coil assembly, it's easier than trying to do this procedure with the coil assembly still mounted in the receiver.

Once the RF coil is removed, installing the shims is easy. I use a pair of channel locks to gently lift the rotor (with the hex collar installed so it will only move just high enough.) I then slide in four shims. Now, release the channel locks and remove the hex-collar. The slotted end shaft will be at the correct height (for the hex-collar to be sweat-soldered in place.) The slotted end of the shaft has to be cleaned with a small jeweler's file but don't clean all the way down to the stationary spacer. Just the upper half of the shaft should be cleaned. Add some slight grooves with the file for the solder to adhere to better. The inside of the split hex-collar must also be cleaned with the small file.

I used a large soldering iron to "tin" the slotted shaft (250W Weller.) If the hex-collar now won't fit on the shaft then file off some of the solder until the hex-collar does fit entirely onto the shaft with the bottom of the hex-collar flush with the stationary spacer. Heat the hex-collar and shaft with the soldering iron until it's hot enough that a very small amount of solder can be melted. This solder will be wicked between the hex-collar and the shaft and should provide a very strong bond. Add a little more solder to the top slot area and create a slight solder "dome" on the top. Let the solder cool and remove the shims.

I used a Dremel tool with a small cut-off wheel to make a slot in the solder. This slot has to be widened by gently using a hacksaw blade (blade alone - not the entire hacksaw.) Test the trimmer rotation using a blade screw driver. It should now adjust correctly. Check all of the wires and components on the RF coil assembly to make sure there's been no damage during the repair. If it looks okay, then reinstall the RF coil assembly into the receiver.  Oct 27, 2017

photo right:   Finished hex-collar repair showing the slot cut to allow adjustment of the trimmer when RF coil is fully assembled.

Another Problem with Band 3 - Band 2 was performing very well after repairing the two defective trimmers. However, Band 3 still seemed to be lacking sensitivity. Injecting a modulated signal into the Antenna Input revealed that the RF trimmers were all working correctly on Band 3. Switching off the modulation and switching to CW (BFO on) should have resulted in a heterodyne signal but no change was noted in the signal. I adjusted the frequency to the top end of Band 3 (sig gen and receiver) and adjusted the BFO trimmer and what happened wasn't unexpected. Of course, the trimmer rotor dropped as soon as it was unmeshed. The non-operational BFO had seemingly reduced the sensitivity because no signals could be demodulated. To repair the BFO on Band 3 is very similar to repairing the split hex-collars on the RF coils since it's exactly the same type of trimmer.   >>> >>>   The BFO coil assembly for Band 3 and Band 4 was removed from the receiver. The trimmer was repaired per the procedure shown above. After the BFO assembly was reinstalled, the BFO didn't work on either Band 3 or Band 4. This could only have been caused by the common return for both trimmer capacitors. I ended up removing the BFO coil assembly again, just to check it over closely. I found a questionable solder joint on the common buss wire return that looked like it might have been cracked but that should have only affected Band 3. Before I reinstalled the coil assembly, I carefully resoldered all of the coil wire wraps to the terminals as a precaution. I installed the coil assembly and soldered the four buss wire connections and the stranded wire return connection. Upon testing, both BFOs worked. The problem was probably due to the coil wire wraps around the terminals as these looked like questionable solder joints. The shield cover was installed and then the BFOs adjusted for 1kc above the tuned frequency on Band 3 and Band 4.         Oct 29, 2017
Trimmer Capacitors Split Hex-collars -  Notes - This splitting of the hex-collar on this style of trimmer condenser is fairly common. This type of trimmer was very popular in the mid-thirties up into the mid-forties. They're found in Hammarlund Super-Pro receivers (they are a Hammarlund part - "ACP" Trimmer,) all BC-348 receivers other than Q, N and J versions, Navy RBB and RBC receivers, on and on. It's likely the problem is due to poor storage conditions and metal fatigue due to age. When the metal was new the hex-collar could expand and contract with varying temperature cycles. However, years and years of thermal cycling will cause the metal to become brittle and eventually it will crack. Poor storage in garages or sheds only results in thermal cycles that are even more extreme and rapidly cause the metal to become brittle. There isn't much that can be done today except to repair the trimmers as they are encountered.
Alignment - The hex-collar trimmer repairs resulted in the RBA-1 now being fully functional. The receiver requires a specific "dummy antenna" to load the input regardless of the impedance of the signal generator. Luckily, the schematic of the "dummy antenna" is included in the NAVSHIPS manual. The parts required are one 20uH inductor, one 400 ohm carbon resistor, one 200pf capacitor and one 400pf capacitor. The schematic is shown to the right.

The trimmers are all adjusted at the top end of each band. For example, on Band 4, set signal generator to 600kc. Set receiver to 600kc. With signal input to antenna input thru dummy antenna, adjust all Band 4 trimmers for maximum deflection of the DB meter. Reduce the GAIN control to compensate as the signal level increases. Use lowest signal input that gives an indication on the DB meter set at the lowest scaling. This is repeated for each band.

The BFO is aligned at the top end and the bottom end of each band. With 600kc unmodulated input and receiver tuned to 600kc, switch on BFO. A 1kc heterodyne should be heard. Adjust BFO 4 trimmer to 1kc heterodyne, if necessary. Tune to 235kc and set generator to 235kc. A 1kc heterodyne should be heard.   >>>

>>>   There are adjustments for the BFO inductance for each band that are "thru the front panel." Two holes are under the tuning chart (Left = BFO 3 and Right = BFO 1) and the two other holes have acorn head screw plugs that are removed to access the holes (Left = BFO 4 and Right = BFO 2.) Adjust BFO 4 inductance for a 1kc heterodyne, if necessary. Check both the upper and the lower frequencies to verify that the BFO is actually 1kc higher than the tuned frequency. Tune the receiver up about 1kc higher in frequency and the BFO should be zero beat if it is set 1kc higher than the tuned frequency. Repeat the adjustments until BFO tracks. Repeat the procedure for each band.

Is the Dummy Antenna Really Necessary? - When the RBA-1 was in service and being aligned at a USN depot, it was unknown to the radio repair technicians what type of antenna was going to be connected to the receiver. Shipboard antennae were quite different from USN land station antennae. What the Dummy Antenna does is provide a somewhat constant impedance load to the receiver that behaves more like a typical antenna would than a direct connection to the Signal Generator output would. The variability of what type of signal generator was used probably also entered into the alignment problems. Using the Dummy Antenna generally ensured that every RBA would come thru alignment with the same performance specification regardless of where it was going and what type of antenna it was going to be used with. Today, most of us are going to use one specific antenna with the receiver. If it's an end-fed wire of considerable length, it might be better to align the receiver with this antenna connected. Couple a signal generator output to the receiver's antenna input by using a small "antenna" on the signal generator output consisting of a three foot wire that's near the receiver. This will provide a frequency specific signal that can be adjusted for amplitude, frequency and modulation (if needed.) This simulates the receiver actually "picking up" a transmitted signal and aligning the receiver for the best operation with the antenna the is going to be used. In this type of set-up, the load of the antenna is just as it is when the receiver is in operation. This then provides an alignment that is exactly for the actual antenna that is going to be used. Tuned loops are a bit more difficult and experimentation would probably be best with these types of antennae. Usually, the loop can be tuned for the highest frequency on the band and then the receiver aligned to that impedance load. Since there is no alignment adjustment for the low end of the band, check to see if when the loop and the receiver are tuned to the low end of the band that the performance is the same as the upper end. When experimenting with various antennae and alignment, only the antenna coils will be affected and only those coils will require adjusting.
Cabinet Restoration - I really didn't want to do an entire respray of the cabinet. If I did, it wouldn't match the receiver front panel. There was a lot of paint missing, especially on the top. The first step was to remove the two data plates and then to clean the cabinet's remaining paint with a brass wire brush and Glass Plus. I then used black nitrocellulose lacquer to repaint all of the areas that were bare metal. I let this set for a day. The next step was to mix a very thin batch of lacquer and thinner - about 2:1 ratio. With gloves on, I then used a cotton pad saturated in thinned lacquer to "go-over" the entire cabinet. This hides the "touch-ups" and ends up with the cabinet looking in good original (although "touched-up") condition. I then reinstalled the data plates and installed the receiver into the cabinet.  Antenna Connection to Navy Coax Fitting - These Navy coax fittings are not common making them difficult to find. There are two easy ways to connect an antenna feed line to the RBA (or the RBB or RBC) that allow use of coaxial cable and provide a good connection to the receiver. Use a double female SO-239 adaptor. The outer diameter will just fit into the Navy coax barrel. It will slightly "thread" itself and make good electrical contact. However the pin at the bottom of the Navy fitting is too far away to make positive contact with the center conductor of the SO-239 adapter. I usually roll .010" thick brass or copper sheet metal into a tube. The tube can then be inserted into the SO-239 adapter center barrel. The other end of the tube should be about a .375" extension and the open end of it will fit over the Navy center conductor pin.

Another way to connect coax is to use a female banana pin plug (these do fit onto the Navy center conductor pin.) The coax center conductor can be soldered to the female banana plug. The shield can have a drain wire soldered to it and it can be connected to the ground lug on the back of the RBA cabinet. 

Performance - Since I had the RBA-1 set up out in the shop, I had to use the 270 foot long, center fed dipole. Since the antenna is fed with open transmission line, I just disconnected the two wires from the antenna coupler and, using clip leads, shorted them together and then used a single 14 gauge stranded wire to connect the feed line to the receiver. Perhaps this acts like a large "T" antenna that has the 77 feet of feed line acting somewhat as a vertical with a large 270 foot long "top hat." The "T" configuration was a popular antenna during the early days of radio.

During some of my initial testing and troubleshooting I tuned in BO 359kc, the NDB from Boise, Idaho - and this was during the day! Quite a surprise,...but when I aligned Band 3 to the antenna, I tuned in HDN 211kc in Gooding , ID, HLE 220kc in Hailey, ID and TCY 204kc in Tracy, CA - during mid-day! Additionally, the normal daytime copy of FCH 344kc in Fresno, CA, MOG 404kc in Montague, CA and CC 335kc in Concord, CA were all present. None of these were newly copied NDBs but I've never heard BO, HLE, HDN or TCY during the day. The next day, I tuned in DC 326kc in Princeton, BC, Canada. Incredible! This was at 13:30 in the afternoon and I was hearing British Columbia. Another note, these stations were being copied on loudspeaker, not 'phones. More experimenting with other LW receivers will be necessary to determine if this is RBA-1 performance (unlikely) or if it's antenna performance (likely.)

Other daytime copies included the USN MSK stations NLK 24.8kc in Jim Creek, WA, NAA 24.0kc in Cutler, ME, NPM 21.4kc in Lualualei, HI and, although substantially weaker, HOLT 19.8kc in Exmouth, Australia. These are very strong stations that are easy copy, day or night.

The INPUT CLPG and ANT COMP. controls are very important and must be adjusted for each band. In fact, the ANT COMP. should be peaked every 10kc or so.

The OUTPUT control and OL switch are used as an audio AVC. Once set, the audio output won't increase beyond the level set. When there's a lot of static crashes or "popping" noises, the OUTPUT (limiter) control helps keep your ear drums intact when using 'phones.    Nov 1, 2017

The following is a log of the stations tuned with the RBA-1 using the 270' CF with 77' of ladder line with wires shorted together. There are six listening sessions within about a seven week period that include both daytime and nighttime listening periods. With the six sessions, I tuned in 100 different NDBs of which six were newly heard stations. Greatest DX was DDP 391kc in Puerto Rico which isn't unexpected since it runs 2KW. Other DX (for a western US location) was FIS 332kc in Key West, FL, YMW 366kc in Maniwaki, Quebec and DB 341kc in Burwash Landing, Yukon. Daytime copy of British Columbia stations YZA 236kc and DC 326kc was unexpected but was certainly due to the time of year. Best LW reception is usually in November and December. The large antenna was probably also a factor. Maybe the RBA-1 was a factor, too.

RBA-1, CFT-46154, SN: 972   NDB Log

Antenna is 270' CF with 77' ladder line with feedline wires tied together.   Height is 40 feet.   Stations are listed in "as heard" order.   Pacific Time.   Newly Heard NDBs - Maroon with asterisk. Unless otherwise indicated, all reception is using 600Z ohm 'phones as audio reproducers.

Nov. 3, 2017  05:55-06:35 - Cndx Xlnt, Quiet

Nov. 9, 2017 19:10-19:40 - Cndx Poor, Noisy

Nov. 18, 2017  13:30 - Cndx Xlnt

Dec 23, 2017 19:05-19:50 Cndx Xlnt

1. UAB -200kc - Anahim Lake, BC, CAN
2. IP - 201kc - Mobile, AZ
3. YBL - 203kc - Campbell River, BC, CAN
4. TCY - 204kc - Tracy, CA
5. HDG - 211kc - Gooding, ID
6. LU - 213kc - Abbottsford, BC, CAN
7. QU - 221kc - Grand Prairie, AB, CAN  *
8. HLE - 221kc - Hailey, ID
9. YKA - 223kc - Kamloops, BC, CAN
10. LWG - 225kc - Corvallis, OR  *
11. CG - 227kc - Castlegar, BC, CAN
12. VG - 230kc - Vermillion, MB, CAN  *
13. OKS - 233kc - Oshkosh, NE
14. BR - 233kc - Brandon, MB, CAN
15. OJ - 240kc - High Level, AB, CAN
16. AVQ - 245kc - Tucson, AZ
17. YCD - 251kc - Vancouver Is., BC, CAN
18. LW - 257kc - Kelowna, BC, CAN
19. HCY - 257kc - Cowley, WY
20. SLE - 266kc - Salem, OR
21. YK - 269kc - Castlegar, BC, CAN
22. XS - 272kc - Prince George, BC, CAN
23. GYZ - 280kc - Guernsey, WY - USCG
24. CEP - 278kc - Ruidoso, NM
25 QD - 284kc - The Pas, MB, CAN
26. EKS - 286kc - Ennis, MT
27. YYF - 290kc - Penticton, BC, CAN
28. TOR - 293kc - Torrington, WY  *
29. TV - 299kc - Turner Valley, AB, CAN
30. ONO - 305kc - Ontario, OR
31. UNT - 312kc - Penticton, BC, CAN  *
32. DC - 326kc - Princeton, BC, CAN
33. POA - 332kc - Hilo, HI
34. RYN - 338kc - Tucson, AZ
35. ZU - 338kc - Whitecourt, BC, CAN
36. DB - 341kc - Burwash Landing, YK, CAN
37. BKU - 344kc - Baker, MT
38. FCH - 344kc - Fresno, CA
39. SBX - 347kc - Shelby, MT
40. NY - 350kc - Enderby, BC, CAN
41. AL - 353kc - Trina, WA
42. MEF - 356kc - Medford, OR
43. BO - 359kc - Boise, ID
44. YQZ - 359kc - Quesnel, BC, CAN
45. RPX - 362kc - Roundup, MT
46. 6T - 362kc - Foremost, AB, CAN
47. DPY - 365kc - Deer Park, WA

WH2XVN copied on 183kc at 05:57

1. ZQ - 410kc - Sir Wilfred Laurier CCGS, BC, CAN
2. MW - 408kc - Moses Lake, WA
3. MOG - 404kc - Montegue, CA
4. QQ - 400kc - Comox, Vancouver Is, BC, CAN
5. SB - 397kc - San Bernardino, CA
6. ULS - 395kc - Ulysses, KS
7. DDP - 391kc - San Juan, Puerto Rico
8. YWB - 389kc - West Bank, BC, CAN
9. JW - 388kc - Pigeon Lake, AB, CAN
10. WL - 385kc - Williams Lake, BC, CAN
11. PI - 383kc - Tyhee, ID
12. GC - 380kc - Gillette, WY
13. OT - 378kc - Bend, OR
14. EHA - 377kc - Elkhart, KS
15. EX - 374kc - Kelowna, BC, CAN
16. LV - 374kc - Livermore, CA
17. MF - 373kc - Rogue Valley, OR
18. HQG - 365kc - Hugoton, KS
19. DPY - 365kc - Deer Park, WA (2nd copy)
20. RPX - 362kc - Roundup, MT (2nd copy)
21. BBD - 380kc - Brady, TX
22. AP - 378kc - Active Pass, BC, CAN
23. MR - 385kc - Monterey, CA
24. HAU - 386kc - Helena, MT
25. CSB - 389kc - Cambridge, NE
26. PNA - 392kc - Pinedale, WY
27. DQ - 394kc - Dawson Creek, BC, CAN
28. FN - 400kc - Ft. Collins, CO

29. MM - 411kc - not on Navaid (MW w/o the dit?)
30. INUU - 395kc - I've copied this beacon many times but have never found it on any Navaid

NOTE:  Conditions were particularly noisy due to a passing storm front and wind causing severe antenna static. One of the problems with using an outdoor antenna. Even indoor loops will respond to weather fronts however.

 Nov. 17, 2017,  19:00 - Cndx Poor

1. FS - 245kc - Sioux Falls, SD
2. YZA - 236kc - Ashcroft, BC,CAN
3. XC - 242kc - Cranbrook, BC , CAN

High level of static from passing front. Static was so bad that OL didn't help. These are new copies for RBA-1 only.

As an illustration of how fast signal cndx can change, I was running the RBA-1 in the early afternoon on the loudspeaker. Copied for long time periods the following stations,...

1. HLE -221kc - Hailey, ID
2. HDG - 211kc - Gooding, ID
3. YZA - 236kc - Ashcroft, BC, CAN

The static level was very low and these stations were easy copy on loudspeaker. This was at 1:30PM in the early afternoon!

Nov. 22, 2017   21:10-21:40 - Cndx OK

1. LU - 213kc - Abbotsford, BC, CAN
2. RL - 218kc - Red Lake, ON, CAN - #
3. QU - 221kc - Grand Prairie, AB, CAN
4. YKA - 223kc - Kamloops, BC, CAN
5. DN - 225kc - Dauphin, MB, CAN - #
6. CG - 227kc - Castlegar, BC, CAN
7. VG - 230kc - Vermillion, MB, CAN
8. YZA - 236kc - Ashcroft, BC, CAN
9. AVQ - 245kc - Tucson, AZ
10. YCD - 251kc - Van. Is, BC, CAN
11. HCY - 257kc - Cowley, WY
12. LW - 257kc - Kelowna, BC, CAN
13. YK - 269kc - Castlegar, BC, CAN
14. GUY - 275kc - Guymon, OK - #
15. CEP - 278kc - Ruidoso, NM
16. YYF - 290kc - Penticton, BC, CAN
17. TOR - 293kc - Torrington, WY
18. ONO - 305kc - Ontario, OR
19. VC - 317kc - LaRonge, SK, CAN - #
20. MA - 326kc - Midland,TX - #
21. DC - 326kc - Princeton, BC, CAN

Static level was moderate even though weather and wind were calm. Most are repeat copy but five new stations to this receiver (marked with #.)

Total NDBs copied with this RBA-1 = 100

Total newly heard NDBs = 6
1. GDV - 410kc - Glendive, MT #
2. MW - 408kc- Moses Lake, WA
3. QQ - 400kc - Comox, BC, CAN
4. ENS - 400kc - Encenada, BCN, MEX #
5. FN - 400kc - Ft. Collins, CO
6. DQ - 394kc - Dawson Creek, BC, CAN
7. YWB - 389kc - West Bank, BC, CAN
8. WL - 385kc - Williams Lake, BC, CAN
9. HAU - 386kc - Helena, MT
10. YPW - 382kc-Powell River, BC,CAN#
11. GC - 380kc - Gillette, WY
12. K2 - 378kc -Olds-Didsbury, AB, CAN#
13. EX - 374kc - Kelowna, BC, CAN
14. YK - 371kc - Yakima, WA#
15. YBV - 370kc - Berens River,MB,CAN#
16. SX - 367kc - Cranbrook, BC, CAN#
17. YMW - 366kc - Maniwaki, QC, CAN#
18. HQG - 365kc - Hugoton, KS
19. AA - 365kc - Fargo, ND#
20. BF - 362kc - Nolla-Seattle, WA #
21. PTT - 356kc - Pratt, KS#
22. IN - 353kc - International Falls, MN #
23. PG - 353kc - Portage, MB, CAN #
24. SBX - 347kc - Shelby, MT
25. MNC - 348kc - Shelton, WA #
26. FCH - 342kc - Fresno, CA
27. RYN - 338kc - Tucson, AZ
28. LF - 336kc - LaSalle, MB, CAN *
29. FIS - 332kc - Key West, FL #
30. DC - 326kc - Princeton, BC, CAN
31. MA - 326kc - Midland, TX
32. YQF - 320kc - Red Deer, AB, CAN #
33. VC - 317kc - LaRonge, SK, CAN
34. YYF - 290kc - Penticton, BC, CAN
35. EKS - 286kc - Ennis, MT
36. CEP - 278kc - Ruidoso, NM
37. XS - 272kc - Prince George, BC, CAN
38. YK - 269kc - Castlegar, BC, CAN
39. ZSJ - 258kc - Sandy Lake, ON, CAN #
40. ZYC - 254kc - Calgary, AB, CAN #
41. YCD - 251kc - Vancouver Is.,BC, CAN
42. FS - 245kc - Sioux Falls, SD
43. YZA - 236kc - Ashcroft, BC, CAN
44. FOR - 236kc - Forsyth, MT

Xlnt cndx. One newly heard "LF 336kc" and 19 new copies for this receiver marked with #.

RBA-2/CFT-46154 SN: 168 - This receiver was being hauled around Carson City, Nevada in the back of a Ford Explorer for many months (maybe longer.) The storage inside a vehicle actually was pretty safe and much better than if the receiver had been stored in a shed or garage where all sorts of contaminates and accidents could be possible. At any rate, I purchased the receiver and power supply right out of the back of the Explorer. Condition is typical "unrestored" which is okay since that means it hasn't been worked on other than maybe at a Navy depot sometime in the past. That's an obvious conclusion since the D.C. VOLT meter is a field replacement "Simpson" in place of the original Weston Type 506 meter. The oval brass tag just above the dial bezel is a Navy asset tag. The glass on the DB meter is cracked. The data plate on top of the cabinet is not mounted but it is the original piece with matching serial number. The USN acceptance tag is also present on top of the cabinet. The crank-handle is missing from the tuning knob which is typical of nearly all RBA receivers. There wasn't the armored power cable although there is an unused connector on the power supply. Also, no AC power connector or cable.

Inside, the RBA-2 looks very clean appearing to be complete and original.

The photo to the left shows the RBA-2 and power supply "as found" without any cleaning or dusting.

Purchased October 2019.

More details when this project gets started.

NAVY-RADIO.COM - For the most detailed information WWII Navy Longwave gear and on all types and all vintages of Navy LW radio equipment, Navy LW radio stations with vintage photographs - go to   Nick England's incredible Navy-Radio website has the most information available. 


Mackay Radio & Telegraph Company

for the

U.S. Coast Guard

Radio Receiver Type RC-123   sn: 97

CONTRACT: TCG-34199   ORDER: CG-80609

built by: Federal Telegraph Co.

15kc to 635kc


photo above
: The Federal Telegraph Company building in Palo Alto around 1927

Mackay Radio & Telegraph Company, Federal Telegraph Company and Federal Telephone & Radio Company - Mackay Radio & Telegraph Company was founded by Clarence Mackay, son of John W. Mackay, one of the "Big Four of the Comstock" fame in Virginia City, Nevada. John Mackay made his wealth in Comstock silver but in 1883 he partnered with J. Gordon Bennett and started in the wire telegraph communications business. Mackay-Bennett started Commercial Cable Co. for trans-Atlantic wire telegraph, although the Mackay-Bennett system used a visual indication code rather than an aural system. Soon, Postal Telegraph was created to compete with Western Union (Postal used the standard American Morse code.) When John Mackay died, he was in the process of laying the trans-Pacific cable for service to Asia (1902.) Clarence inherited the business, finished the trans-Pacific cable (1904) and, in 1925, added radio to the world-wide communications system. In 1928, Clarence sold most of his business holdings to International Telephone & Telegraph Company (ITT.) Mackay remained on as head of Mackay Radio and Telegraph Company until his death in the late-thirties.

Federal Telegraph started out in Palo Alto, California mainly dealing in arc transmitters. At one time, Lee DeForest worked for the company but Frederick Kolster was the chief engineer for most of FTC's history. FTC bought the Brandes Company and created a new division of FTC called Kolster Radio Company specifically for selling consumer radios in the mid-twenties. FTC became involved with Mackay Radio in 1926 when Mackay bought a radio station that had belonged to FTC. When Mackay sold his interests to ITT, Federal Telegraph Company continued to do most of the Mackay Radio work under contract to ITT and eventually, in 1930, ITT bought Federal Telegraph. ITT moved the Federal Telegraph operation to Newark, New Jersey in 1931. For awhile ITT tried the consumer radio market with a division called Kolster International but it was a short-lived venture. The name of Federal Telegraph Co. was changed to Federal Telephone and Radio Company during the early days of WWII (about 1942.)

After WWII, Mackay Radio equipment usually indicates "built by Mackay Radio & Telegraph Company." Since ITT owned both Federal Telephone and Radio Company and Mackay Radio, it's assumed that ITT believed showing both companies as involved with the production was superfluous information. Later, Mackay Radio became ITT-Mackay Marine.

General Information Radio Receiver Type RC-123 - The Mackay RC-123 is a six-tube, regenerative receiver that tunes from 15kc up to 635kc in four tuning ranges. The power to operate the receiver was supplied by ship's DC power for B+ (115vdc) and batteries for the tube heaters. It was also possible to operate the receiver entirely on batteries in which case dry cells were used for the B+ requirements. It was also possible to operate the receiver entirely on 115vac. To operate the tube heaters on AC, a small 115vac to 6.3vac transformer was mounted inside the cabinet and could be connected into the circuit using the terminal strip located in the rear of the cabinet. If the RC-123 is operated on AC, an external 1:1 isolation transformer should be used since a power transformer is not part of the B+ circuitry. The tube heaters are connected in parallel and the two dial lamps are also part of this circuit (#47 specified.) The pilot lamp operates from the internal ballast in the 35Z5 tube and is also a #47 bulb. The RC-123 receiver is specified as a Mackay Type 128-AZ with two changes. First, the audio output tube's plate circuit is transformer coupled and provides a 600Z ohm output at the phone jack and at the audio output terminals available inside the cabinet (for routing to a console output or operator's desk jack.) If compared to the common Type 128-AY, that receiver's audio output was coupled via a plate capacitor providing a Hi-Z output. The other change is specific to the difference compared to the 128-AZ and refers to the 6.3vac transformer for the tube heaters that is mounted inside the cabinet (the "AY" version does have this tube heaters transformer.) No reception filters are provided for relief from static crashes or other atmospheric noise. "Mackay Radio" isn't shown anywhere on the receiver. The "triangular shield" logo is the only indication that Mackay was involved in production. However, at the bottom of the panel is "built by Federal Telegraph Company, Newark, N.J., USA" which indicates the RC-123 pre-dates the FTC name change that happened during the early part of WWII.

photo right: top of the RC-123 chassis

Serial Number 97 Inspection - The RC-123 superficially looked pretty rough. Only close examination revealed its true condition. The dial cover plastic was very dark amber-brown (looking barely transparent) and it was severely cracked and broken. The panel was darkened with over 75 years of "aged cigarette smoke" deposits that almost obscured the panel nomenclature. The cabinet was extremely dirty and stained along with having been painted light gray over the original very dark gray (almost black) wrinkle finish. However, when the chassis was extracted from the cabinet, the condition assessment started to change for the better. The chassis was in very nice condition with no corrosion at all. All of the components were original with only a few exceptions. The RF Gain pot had been replaced with an incorrect value and the NE-2 Antenna Input protection bulb was missing. It was also noted that one knob, although very close in appearance, wasn't an original type. Closer examination was going to be required on L3, an antenna coil for Band C which appeared burned. The coil still had continuity (I don't know what I measured, actually had an open primary winding) but its actual usability has to be determined when the receiver is functioning. The best surprise was when the darken, broken plastic dial cover was removed it was discovered that underneath the dial itself was in near-perfect condition.

Underneath the chassis, as mentioned, the RF Gain pot was a 25K with a series 25K resistor that needed to be replaced with an original 50K WW pot. There was a length of brown "zip cord" that had the exterior end cut and the interior end was connected across C27 at the component board directly behind the Audio Gain pot. This had the two wires connected to the 6K6 output tube's plate and screen and that also was the connection of the primary of the audio output transformer T2. The purpose of this "zip cord" is unknown, and it wasn't original, so it was removed. As received, the RC-123 had a glass 6SK7GT tube installed for the RF amplifier. This was replaced with a metal 6SK7 tube. All other tubes tested good.

photo left: Underneath the RC-123 chassis. This photo was taken before the rebuild. Note the two upper-most coils, L3 and L4. Note the "wax spatter" on the metal mounting bracket (right coil, L3) indicating where the coil had gotten hot - fast! Note on left coil, L4, how the coil primary is discolored and dark, also indicating high heat.

Panel Cleaning - Tobacco stains are difficult to remove mainly because the discoloration has affected the paint itself. Fortunately, the discoloration normally isn't too deep and if the original paint was applied with heavy coats then one can gently remove just a thin part of the surface which eliminates the tobacco staining and somewhat returns the paint to its original tint. The method used sound harsh (and it can be) but if carefully done it results in an improved appearance to a tobacco-damaged panel.

I use plenty of Glass Plus and 0000 steel wool. Keep the panel very wet with the Glass Plus and gently rub the 0000 steel wool in a "figure-8" pattern. This "figure-8" will avoid linear scratching and evens the paint surface removal. Don't scrub the surface and check the progress by washing the panel with Glass Plus and a paper towel frequently. It takes 20 to 30 minutes of this treatment to remove significant tobacco staining BUT it only works on smooth, non-glossy paint, so this process is pretty limited but the Mackay panel paint was this type and the tobacco-stains were 95% removed.

Dial Rebuilding - When disassembling the receiver to remove the front panel one really has to be observant as to how the various parts of the dial assembly are mounted. There are two identical gray colored full-size spacers, one mounts on the front panel and the other is near the back of the "stack" of pieces. From the rear dial frame forward,...first is the dial scale, then one of the two gray metal spacers, then the black spacer. These are mounted behind the front panel. On the front of the panel is the transparent plastic dial cover and then the second gray spacer. The dial pointer has to be in front of the black spacer. There are two washers used as spacers between the rear dial frame and the back gray spacer (two top screws only) to compensate for the thickness of the dial scale material. If the front panel is mounted to the chassis then you can't get the dial scale or the black spacer installed (or removed) because of the dial shaft. The procedure is to loosen the set screws on the dial shaft coupler and slide it back onto the tuning condenser shaft as far as possible. Then loosen the set screw for the vernier reduction and pull it forward off of the dial shaft coupler pin. This allows the entire dial frame and vernier unit to be removed allowing installation of the entire dial assembly. When installing the dial assembly be sure to mechanically "zero" the dial pointer with the fully meshed tuning condenser.

I had to make a new transparent plastic dial cover which is just a flat plastic piece about .020" thick. The vernier reduction unit was lubricated with heavy grease applied with a small brush and worked into the pinch wheels. The dial scale is made out of a celluloid plastic that reacts to water or water-based cleaning. Too much water will begin to dissolve the celluloid. I dry cleaned the dial scale using just a clean flannel cloth to remove the loose dirt. Luckily, the dial scale was in good shape and didn't need a lot of cleaning anyway.

Cabinet Wiring - There are several connections that can be utilized inside the RC-123 cabinet. All four fuses for the LINE+, LINE-, DC B+ and DC A+ are on a bracket mounted to the rear of the cabinet. The fuse holders are the long-shaft type with the screw-in top. These types have a real tendency to break the side connection due to the flimsy design. Two of the four fuse holders had broken side connections. A search of the "fuse holder junk box" turned up two exact replacements that were in good condition. As usual, the fuses inside the holders weren't all the correct current ratings. The LINE fuses should be and were 1A, but the DC B+ should be 1/8A and a 1A was installed and the DC A+ should be 5A but a 10A was installed. Correct fuses were installed in all holders (even though DC operation wasn't anticipated.)

Another problem was the 6.3vac output wiring from the "tube heaters" AC transformer. The wires had be cut and then the ends were wrapped with plastic electrician's tape indicating a non-vintage alteration. That the AC tube heaters supply was removed indicates that some other source was used or intended to be used to power up the receiver. Fortunately the cuts were only about 2" from the transformer and there was ample wire available on the other end to make new connections that were stripped, tinned and soldered to the transformer.

To power the RC-123 on AC requires a power cable be wired to the LINE+ and LINE- terminals on the power strip inside the cabinet. There's a "knock-out" just below these terminals for access. Also, the antenna connections are routed through the back of the cabinet and connect to "M" and "G" on the antenna terminal strip. "E" and "EXT" are connections for the emergency antenna (E) and a connection for another receiver (EXT) to share the emergency antenna. There is another terminal strip that provides an external connection for the 600Z audio output to run to a console or to a phone jack on the operator's desk.

Cabinet Paint - The interior and the exterior bottom were still the original dark Mackay gray but the two sides, the back and the top had a coat of light gray paint applied. The paint job was definitely of poor quality but not bad enough for a total repaint. Besides the correct color would require a wrinkle finish base coat and a matched color top coat. The existing paint was thoroughly cleaned using a brass brush and Glass Plus. This was allowed to dry for several hours. I then matched the dark Mackay gray using Artist's Acrylic paint. I mixed a fairly large amount in a small cup and thinned the paint with water. Then using a paint-dampened sponge I dabbed the thinned paint onto the cabinet. This process takes awhile because the paint goes on so thin. The sponging action allows the "wrinkle" to still show through the paint. It usually takes a couple of coats of sponging the acrylic paint onto the cabinet to get the color correct. Sometimes the paint will seem to separate and look a little "foamy" but when it dries it will look correct. The disadvantage of this type of paint treatment is that Artist's Acrylic isn't a very durable paint. Once it's dry, you can wipe the cabinet with a dry flannel cloth but you can't use any dampened cloth for at least a week or so. Also, Glass Plus (and certainly Windex) will attack the paint so dry-cloth dusting is the safest approach. The cabinet will have a matte finish and the wrinkle will show. It's about the easiest way to get a "color match" on wrinkle paint without going through an entire repaint job.

Shock Mounts - The manual shows the typical WWII type shock feet installed directly to the bottom of the cabinet. I used a set of WWII shock feet I had purchased for another receiver but never used.

Power-on Testing, L3 Primary and other Problems - As mentioned in the "inspection" section above, L3 looked like the primary winding had gotten very hot. L3 actually splattered wax on the band switch shield panel because it had gotten so hot so fast. Probably lightning damage, especially since the NE-2 static drain bulb was entirely missing (wires were there but the bulb was gone.) Only band C seemed to be affected. Bands D, B and A functioned more or less correctly (I thought.) I measured the B+ at only +12vdc but after re-reading the manual I noted that if an isolation transformer is used then the LINE- should be tied to chassis ground. When that connection was made the B+ went up to +40vdc,...just a third of what it should be. As a test, I "tack soldered" two 10uf electrolytic caps in parallel with the dual 8uf can electrolytic. That got the B+ up to +130vdc about where it should be. The receiver then began to function somewhat normally. Regeneration, RF Gain and AF Gain all worked normally. I tuned in WWVB 60kc (strong signal) and KPLY 630kc (strong signal, sort of) as a test that the RC-123 was basically working with the exception of Band C and that fault was the open primary winding on L3. 

Rewinding L3 Primary - When attempting to repair a coil the first thing to try is a close examination to see if perhaps it's something easy, like a break. Unfortunately, the primary was wound with Litz wire and the heat-damage made it difficult to find any single break. Several breaks were found and the heat apparently had made the wire very brittle. Examination looked like the Litz wire had about ten strands. The coil looked like it was about 12 layers deep. The DC resistance should be 2.8 ohms. I salvaged a Litz wire wound LF coil out of a derelict RBH receiver coil box. Since this coil measured about 8.0 DC ohms there would be plenty of wire to wind a new primary coil for L3. The burned primary winding was removed and the form cleaned. The original wrap was the "zig-zag" type that requires a mechanical coil winder (like a Morris, which I don't have.) Since this was only a primary winding, I just layered the windings and tried to keep all of the layers equal. To measure the DCR of Litz wire all of the strands have to be soldered together for an accurate measurement. Two times checking and the second check measured 3.0 ohms which was close enough. I installed new black sleeves and then soldered the ends to the terminals. I then coated the entire primary coil with bee's wax, as original. Before installing the repaired coil, I rechecked the DCR and the primary was 3.0 ohms and the secondary was 14.8 ohms, both close to what is shown in the manual. With L3 installed, the RC-123 now "came alive" on Band C, not that there's an abundance of signals from 100kc up to 240kc but the signal generator proved that Band C was working correctly. An alignment of Band C improved reception significantly. Band D was also aligned. Band B and A are aligned together using a trimmer located on the tuning condenser stator B.

Rewinding L4 Primary - In comparing the repaired L3 signal levels along with the levels on Bands B and A, it was apparent the Band D signals level were far less than those Bands and the Antenna Trimmer had no affect on signal level on Band D. The Antenna Trim worked fine on Bands A, B and C. I measured the DCR per the procedure in the manual and the L4 primary was twice the resistance it should have been (measured 1.8 ohms, should have been 0.8 ohms.) Also, there was very little wax left on the primary wires. I suspect that when L3 got the lightning "hit" there was enough "flash-over" (because of the common chassis connection and low DCR) that it over-heated the L4 primary winding and changed its characteristics.   >>>

photo above: The rebuilt L3 Antenna Coil for Band C in the foreground. The coil at the upper-left is L4, note the burned look of the primary. This photo was taken before L4 was rebuilt.


photo above: L4 primary rewound, rewaxed, reinstalled and working

>>>   Once L4 was removed from the receiver, I had to melt the bee's wax off of the coil to see how it was made. It's a little different in that the primary winding is actually two coils, one on each side of the secondary. The two primary coils are wired in series and consist of a single layer of Litz wire. Although the primary coils had continuity, close examination showed that the cotton (or silk) had burned up completely and had mixed with the lightning-melted wax to make a black matrix that the wire was embedded in (a carbonaceous mixture?) Perhaps this might have been affecting the primary coil field and coupling. It's also possible that the extreme instantaneous heat changed the wire characteristics itself. At any rate, L4 wasn't working as it should.

The secondary winding had to be disconnected from the coil form in order to unwind the lower primary coil. Both primary coils were then unwound. Underneath, the white cloth adhesive tape (that provided a cushion for the coil wire against the coil form) was totally burned and destroyed. I used one layer of white masking tape as a replacement cushion. I rewound the primary coils with Litz wire (as original.) When each single layer was complete the DCR of each was 0.4 ohms, so the two in series would be 0.8 ohms.

Tinning Litz wire is difficult but very necessary to assure that all of the strands are connected together at the terminals. I think new Litz wire would have been easier to work with but the junk RBH coil was easy to access and was the correct size even though it was 80 years old. To tin the Litz wire, careful removal of the enamel insulation is required. I used a razor blade and gently scraped the enamel off. This has to be carefully done so none of the wires are broken. Once clean and shiny, the strands are twisted together, again lightly scraped and then the solder is applied. Even with all of this care, the solder joints at the terminals didn't easily flow over and though the Litz wire. It could have been wax contamination since the bee's wax residue was in every part of the coil. Eventually, with more light scraping, the solder flowed and the joint was decent. Once all the Litz wire ends were soldered to the correct terminals then the entire coil was coated with new bee's wax.

The rewound L4 was reinstalled into the RC-123. First thing noticed,...the Antenna Trimmer now worked. Next, slight changes in the coil itself due to the reworking required a touch-up on the alignment. Now, Band D has much better sensitivity and behaves more or less like Bands C, B and A.

Quick Reception Test - About 2200 hrs (Aug 31, 2020) I performed a quick check to see how the RC-123 would function, even though the capacitors hadn't been replaced. I had performed a resistor check earlier and surprisingly all of the ERIE resistors were within 25% tolerance. During the R-check, I discovered that one end of R5 had never been soldered (grid leak for RF amplifier) and had been relying on a loose wrapped joint for the past 75+ years. Cleaned joint and soldered to correct. During the reception test, I tuned from 405kc down to 325kc to see how certain known NDBs could be heard. MOG 404kc was very strong, QQ 400kc was moderately strong, ZP 368kc moderate signal and DC 326kc was moderate. Conditions were pretty noisy and it's still Summer, so it's not the best time for MW DX. I was using the 135' "T" antenna. The test showed that, more or less, the RC-123 is operating correctly and does receive signals of moderate strength in the MW portions of the spectrum.

Capacitors - There are twelve paper-wax tubular capacitors in the chassis and two in the cabinet. The wax was cracked on many of the cap ends indicating a loss of the sealing property of the wax. Even if the paper dielectric is sealed, leakage current can still develop since it's basically caused by contamination of the paper at the time of manufacture. However contamination problems are accelerated with moisture ingression so these capacitors undoubtedly have some leakage current problems. Any new polyfilm cap is about 1000 times better. All I had on hand in sufficient quantity were "yellow jackets." I usually paint these types because the yellow-color is so terrible-looking,...way too bright, looks like they belong in an imported toy. I painted the new capacitors black and left it at that. There are ten .05uf caps and two .1uf, so it's not too hard to keep track of which value is which. I didn't replace the two capacitors in the cabinet because they are bypass caps for A+ and B+ and are only in the circuit if DC operation is going to be used.

The wrong value RF Gain pot was replaced with a NOS 50K 4W WW Clarostat pot that was identical to the original. The missing original pot was an audio taper. I could only find a linear taper style so the RF Gain adjustment is more towards the top 25% of the range.

Post-Recap Test - At 2220hrs to 2235hrs (Sept 3, 2020) I tuned in fifteen NDBs in fifteen minutes of listening. Antenna was the 135' "T" and I was using 600Z phones for the reproducer. Tuning range was from 408kc down to 296kc. NDB stations heard were the following:

1. MW 408kc - Moses Lake, WA                          9. AA 365kc - Fargo, ND
2. MOG 404kc - Montegue, CA                           10. RPX 362kc - Roundup, MT
3. QQ 400kc - COMOX, BC,CAN                      11. MEF 356kc - Medford, OR
4. PNA 392kc - Pinedale, WY                             12. NY 350kc - Enderby, BC,CAN
5. YWB 389kc - Westbank, BC,CAN                  13. XX 344kc - Abbotsford, BC,CAN
6. PI 383kc - Tyhee, ID                                        14. DC 326kc - Princeton, BC,CAN
7. GC 380kc - Gillette, WY                                 15. LGD 296kc - LaGrande, OR
8. ZP 368kc - Sandspit, QC Is, BC,CAN

Conditions were very good for early September with relatively low noise levels. All stations were easy copy with moderate to very strong signals.

The RC-123 is now functioning as it should. During the LW season peak in late-November through mid-Jan, DX NDBs should be plentiful and fairly easy copy. The receiver is very easy to operate and the tuning rate, although fast, is able to fine-tune signals in the MW portion of the spectrum. Regeneration doesn't have to be adjusted at the feedback point for good sensitivity. This is probably because of the "Regeneration Tube" that amplifies the feedback. Maximum sensitivity is still at the feedback point but slightly beyond that gives good stability and ample feedback. A couple of minor negatives would be that the RC-123 is a very "basic" receiver with no filters for static crashes and no selectivity filters. What you hear is pretty much everything as far as spectrum noise. The other minor point is the dial resolution is extremely vague with 25kc separation of the index marks on Band D. Considering the RC-123 was designed in 1941 and that it was primarily a commercial receiver that was "pressed into" military service, it does a good job with no "fluff" or "frills."



Mackay Radio & Telegraph Company


  Marine Radio Receiver  Type 3001-A

Commercial MW, LF & VLF Shipboard Receiver from 1952

15kc  to  635kc 

SN: 52-M-070


The 3001-A has its original design basics dating from around 1940 with Type 128 Series of Mackay shipboard receivers but this receiver was designed around 1948 and the example shown was built in 1952. The Type 3001-A is significantly updated from the earlier Type 128 and, although many parts are very similar (or even identical) to the earlier receivers, the circuit was substantially changed for better adaptability for commercial shipboard (non-military) use. The Type 3001-A could be set up as the main receiver or as the emergency receiver depending on the ship's requirements. Usually these receivers were installed into Mackay MRU-19/20 shipboard radio console where two 3001-A receivers were used along with HF receivers, HF and LF transmitters and other auxiliary equipment. The 3001-As were panel mounted when installed in the MRU set-ups.

The 3001-A is a regenerative receiver covering 15kc to 635kc in four bands that uses an AC-DC circuit and can operate on 115vac or on DC using batteries. When BATT. is selected, the tube heaters are connected in parallel and a plug-in WW resistor is selected for the desired battery voltage with 6vdc, 12vdc and 24vdc being the most popular options. B+ was supplied by standard dry cell B batteries when DC operation was used. When LINE is selected, the tube heaters are then connected in a series string that includes a four pin Amperite ballast tube (along with the six octal tubes and two dial lamp loads.) An additional tube heater series load is provided by what appear to be dial lamps (they were for dial illumination in the earlier WWII versions) but these lamps are just acting as an additional load since the white dial is an opaque material on the Type 3001-A. A single TRF amplifier (6SK7) is used along with a "regeneration" tube (6J5) that amplifies the tickler coil response in the RF section to improve the feedback level. The regeneration tube's output goes to a detector tube (6SJ7) followed by a first AF amplifier (6SJ7) and then an audio output tube (6G6G.) The cabinet has "knock-outs" all along the back and the bottom-rear to allow routing the various cables necessary for the installation. These would consist of the Main Antenna and Emergency Antenna, the AC power connections, the DC power connections and an external earphone connection. A small built-in speaker provides for radio room monitoring but earphones would normally have been used by the shipboard radio operator.

The 3001-A receiver power is quite different from the earlier 128-AY (or RC-123 above) in that it's a true AC-DC receiver that has a series tube heater string (in LINE op) and a floating B- with the only connections to chassis being the cable shields and B- to chassis coupling capacitors. Although the receiver can be operated directly on a modern AC line (grounded Neutral,) if the AC plug is not polarized, then one does have to be careful that no other grounded equipment is connected to the receiver during testing or measuring (all voltage measurements have to be referenced to B- not chassis.) A 1:1 isolation transformer or a properly oriented (polarized) AC plug can be used to assure that the receiver circuitry is not inadvertently grounded.

These type of Mackay receivers were used onboard ship for decades (there are many reports from the 1990s that the 128 series Mackay receivers were still being used on some ships and a few reports indicate that some may still be in use.)

photo left: Top of the chassis showing the Jones plugs that are for the power (8-pin upper left,) antenna inputs (4-pin) and external phones (2-pin round) to/from the receiver. The large resistor drops 6vdc and is for operation on 12vdc for the tube heaters (BATT operation has tube heaters connected in parallel.) The hole above the 35Z5 tube originally was for a can-type dual section 8uf electrolytic capacitor. The tube to the lower left of the 35Z5 is the ballast tube. Note that the fuses for voltages in are located on the chassis of the 3001-A (they were located inside the cabinet of the Type RC-123.)




photo right: The under side of the chassis showing the various coils and other components. This receiver was partially re-capped sometime in the past. There's a combination of dark pink molded paper caps and some mylar dielectric caps. Also, the can electrolytic capacitor has been removed and a pair of tubular electrolytic caps mounted under the chassis. The large cardboard unit on the left side is the original dual section 8uf paper dielectric filter capacitor.

This Mackay 3001-A was a ham swap meet find purchased in October, 2009 ($25 was a bargain, even then.) The design and construction of the Mackay 3001-A is obviously commercial and is no where near the "cost-no-object" design and "over-built" construction of equipment built for the Navy. Still, the receiver is an impressive performer and has some interesting designs in the circuitry. Tubes used are 1 - 6SK7 RF Amplifier, 1-6J5 Regenerator, 1 - 6SJ7 Detector, 1- 6SJ7 1st AF Amplifier, 1 - 6G6G Audio Output, 1 -35Z5GT Rectifier and 1 Amperite Ballast Tube. Each Detector coil has its own "tickler" winding which is routed back to the RF Amplifier's screen and is controlled by a 50K Regeneration pot. Selectivity is controlled by a combination of the RF Gain setting and the setting of the Regeneration - too much RF Gain results in very broad signals. Best performance is achieved using earphones with the AF Gain fully advanced and using only what RF Gain is necessary to hear the signal. Regeneration should be set just at the oscillation point or slightly into the oscillation range - whichever gives the best signal. The Antenna Trim will somewhat affect the signal tuning and its manipulation can contribute to successful copy on very weak signals. The vernier reduction action of the main tuning dial seems a bit fast at first but in actual use the bandspread of each tuning range is wide enough that the tuning rate works out just fine. Like the earlier Mackay shipboard receivers, the Type 3001-A is a "basic receiver" with no filters for suppressing static crashes or other pulse noise. Also, there are no filters for selectivity or tone enhancement. The tuning dial resolution is vague, especially on Band D where there's 25kc separation between index markers. But, the 3001-A is still a great little receiver (weight is only about 35 lbs) with excellent sensitivity and it is capable of receiving just about anything in the LW spectrum. Besides all of the normal NDBs, this 3001-A also has received the LW BC station from Sakhalin Island on 279kc (off the air Jan 2014) and also JJY 's pulse-coded time signals from Mt. Otakadoya, Japan on 40kc. The Navy VLF MSK stations from Hawaii on 21kc and from Cutler, Maine on 24kc and Jim Creek, Washington on 24.8kc both can received quite well. An impressive receiver that doesn't challenge your back to move.

NOTE: The Type 3001-A sn:52-M-072 shown has a perf-metal grille over the panel speaker. This isn't original. The original speaker grille was a black felt-flocked, wire-mesh grille. The original grille on this receiver was missing most of its flocking and looked terrible. I had a piece of black felt installed and that looked just as bad. I then found this perf-metal grille and it was a perfect fit. It looks a lot better than the original grille but, isn't original. Also, the shock feet are not the original style used. These feet are from some piece of military gear I was parting out. They fit nicely and looked great,...however, they aren't the original type used with the Type 3001-A.



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