Vintage Longwave Receivers - Part 2
10. Profiling the Signal Corps
Army Signal Corps
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.|
||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.
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.
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
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.|
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-2 SN: 168
15kc to 600kc
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.
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
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.
|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.
Mackay Radio & Telegraph
Radio Receiver Type RC-123 sn: 97
15kc to 635kc
||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
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,...it 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
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.
- 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
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.
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
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.
- 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. >>>
||>>> 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
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
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
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,
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,...it 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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