Radio Boulevard
Western Historic Radio Museum


 WWII Radio Communications Equipment 
PART 3

 

Radiomarine Corp. Radio Gear
U.S. Coast Guard Radio Gear
U.S. Army Signal Corps Radio Gear
 WWII Radio Test Equipment
 

 


photo
: Women Marines Radio Op using two RAK receivers

WWII Communications Equipment - Part 3


Radiomarine Corporation Shipboard Radio Equipment from WWII (not built for the Navy)


RMCA AR-8506-B  SN:4387  from 1943

Radiomarine Corporation of America  -  AR-8506-B

The RMCA AR-8506-B was introduced during WWII with schematics dated November, 1942 and with the FCC approval for shipboard use dating from February, 1943. The AR-8506-B is a five band receiver capable of reception of LF signals from 85kc up to 550kc and medium/shortwave signals from 1.9mc up to 25mc. The circuit is superheterodyne and uses 10 tubes along with a NE-32 (G-10) neon lamp for voltage regulation (LO.) The IF is 1700kc in order to allow the receiver to cover the entire 400kc range without interruption. Much of the ship's communications were in the frequency range of 400kc to 500kc and a standard IF of 455kc would have a gap in frequency coverage from about 430kc up to 475kc due to the IF operating at 455kc. Usually, shipboard superheterodynes will have IFs that are in the AM BC band area since this region of the spectrum wasn't normally tuned by the ship's communication receiver. The receiver can be powered by 115vdc or 115vac and can also be powered at 230v ac or dc using an external resistor unit, the RM-9. Tuning uses a 30 to 1 reduction vernier drive (counter-weighted) and there is an additional "band spread" function using a separate control. A built-in loudspeaker is front panel mounted and can be switched off by the operator if necessary. The FCC approval for shipboard use indicated that the AR-8506-B's LO leakage to the antenna was <400pW and thus would not interfere with other shipboard radio equipment and would not radiate a signal of sufficient strength for enemy DF or detection. The U.S. Army Signal Corps issued a manual, TM11-875, giving the AR-8506-B the designation R-203/SR.

These receivers were integrated within a shipboard communications console, generally the 4U, that contained two transmitters, another receiver capable of VLF reception (AR-8510,) an emergency receiver (crystal detector receiver,) a power control switching system that allowed battery operation or ship's power operation, motor-generator operation, various alarms and other equipment necessary for radio communication at sea. Most 4U consoles were installed on Victory ships and other merchant ships during WWII.

Shown to the right is the RMCA 4U marine radio unit. Note the the receiver to the left of the typewriter is the MW-SW receiver, the AR-8506-B, and the receiver to the right of the typewriter is the LF receiver, the AR-8510. The two transmitters are mounted directly above the receivers. Photo is from Sterling's "The Radio Manual" Fourth Edition.

After WWII, the AR-8506-B continued to be offered by RMCA for maritime use on various types of ships. The post-war versions are somewhat different in appearance in that the individual celluloid control identification plates are replaced with a "raised letter" type of panel nomenclature. Additionally, the data plate was removed and the manufacturing information became part of the front panel nomenclature. The AR-8506-B shown in the photo below-left is from 1953 and shows how the later versions looked when installed in the table top cabinet (with shock mounts.) The earlier (WWII - from June 1943) style receiver, using the round celluloid control ID plates, is shown in the upper photo. Ship owner's reluctance to replace radio gear had the RMCA consoles and the associated equipment in-use well beyond their normal life-span with examples still in use as late as the 1980s.

The AR-8506-B has an internal 1700kc wavetrap. The wiring and adjustment of the wavetrap should be checked if BC signal leakage is encountered. The wave trap should be adjusted on Band 3 for minimum response with a 1700kc RF signal input to A1 on the antenna input of the receiver. If it is correctly adjusted and still there is BC signal leakage then using an antenna that is "tuned" for the specific frequency desired should be tried. This could be a resonant antenna cut for the specific frequency desired or an antenna with an antenna tuner. The "tuned" antenna will be selective and should reduce the BC interference.  Like a lot of RCA receivers, the AR-8506-B doesn't have a standby switch (either remote or panel.) Most shipboard radio operations are receive on one frequency and transmit on another frequency using separate antennas so a standby wasn't really necessary. To use as a ham station receiver operating on the same frequency as the transmitter requires either an antenna relay with good isolation for the receiver in "transmit" or you can also use an electronic TR switch. Separate T-R antennas are also a possibility. In all cases, you'll have to reduce the RF Gain and AF Gain or switch off the loud speaker if you're on Voice transmission to avoid feedback.

photo left: AR-8506-B SN:53139. The first two digits on many of the Radiomarine receivers will indicate the year of manufacture, in this case 1953.

 

photo right: Radiomarine LS-1 Loud Speaker SN:4475. The probable year of manufacture is 1944. The switch selects either low impedance or high impedance. DCR in low Z is 5.0 ohms and DCR in high Z is 640 ohms. This would imply that the nominal impedance would be about 10 Z ohms for low and about 8000 Z ohms for high. The case is made of 3/8" solid oak with dovetail joints. This example has the wood painted black but originally the cabinet was painted gray. The speaker is a 3" diameter PM and a matching transformer is also inside the cabinet. I'm not sure whether the LS-1 was for testing applications or if it was for use as a temporary loudspeaker. The cable is about three feet long with a standard 1/4" phone plug on the end. The knob may not be the original style. 

 

Radiomarine Corporation of America  -  Model AR-8510

The AR-8510 is a five tube regenerative receiver that tunes from 15kc up to 650kc in four tuning ranges. Two TRF amplifiers are used with a Regenerative Detector and two stages of audio amplification. The RF amplifiers use a combination of tuned grid and tuned plate with a three-section ganged condenser for tuning. The audio output can drive the panel mounted loud speaker or headsets. The panel speaker can be switched off if only a headset is desired for reception. The receiver requires a separate power source of which many types were available. Various types of battery combinations could be utilized with either the RM-2 or the RM-4 Battery Control panels. These functioned on ships that provided 115vdc or 230vdc power. If 115vac was to be used then the RM-23 Rectifier Power Unit (power supply) was used. There was also an RM-37A Receiver B+ Supply Unit that provided 90vdc output from the ship's 115vdc power. This was to be used if it was necessary to conserve the B batteries that normally provided the +90vdc for the B+. The AR-8510 requires 6.3 volts at 1.8A (AC or DC) and 90vdc at 15mA. The vacuum tubes needed are four 6SK7 tubes and one 6V6G or GT.

The AR-8510 was provided with a cabinet and shock mounts if it was to be used as a "stand alone" receiver. However, if it was going to be installed into a shipboard communications console (as most were) then the cabinet and shock mounts were not provided. Many AR-8510 receivers were part of the shipboard 3U transmitter console that included a 200W transmitter, an emergency crystal receiver, a battery charger switching panel and an automatic emergency alarm receiver. 4U consoles used the RMCA AR-8506 (a MW and SW superhet) and a 500W transmitter. The 5U console had both the AR-8506 and the AR-8510 installed along with all of the other auxiliary equipment. Mackay Radio supplied MRU-19 or MRU-20 consoles with their equipment installed.

The AR-8510 was approved by the FCC for shipboard use in 1942. The schematic drawings are dated 1943. The AR-8510 shown in the photo above is dated NOV 1944 and has a serial number of 2774. The AR-8510 serial doesn't follow the typical RMCA format of having the manufactured year as the first two digits of the serial number. Instead the month and year are stamped on the data plate. This particular receiver was installed in an RMCA console so it doesn't have a cabinet. However it does have a bottom cover that incorporates embossed dimples for feet that allow the receiver to set on a table without scratching.

Most of the WWII installations were onboard Liberty ships. Post-WWII use was for commercial shipboard use. Later versions of the receiver look like the B&W photo to the right. This is from the 1950 manual. Note the "raised letter" nomenclature which is not used on earlier versions. Ease of maintenance during WWII would have had the receivers fitted with the celluloid tags that could easily be removed for repainting the panel or replacement if damaged. After WWII, the "raised letter" panels were probably used since the receiver wouldn't have to endure the rigors of war-time use. Post-WWII use continued for quite some time with AR-8510s showing up on old oil tankers as late as the 1980s.

photo right: The AR-8510 as shown in the 1950 manual.

 

U.S. Coast Guard

Mackay Radio & Telegraph Co. - Federal Telegraph Co.  for  U.S. Coast Guard

Type RC-123

The Mackay Type RC-123 was built for the U.S. Coast Guard on Contract TCG-34199 and Order CG-80609 dating from 1942. The receiver is a six-tube, regenerative RF circuit 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 and usually rechargeable lead-acid batteries for the tube heaters. 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 inside the cabinet. The tube heaters are connected in parallel and the two dial lamps are also part of this circuit (#47 specified.) The red-jewel pilot lamp illumination operates through the internal ballast in the 35Z5 tube and is also a #47 bulb. The Type 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 128-AZ and refers to the 6.3vac transformer for the tube heaters that is mounted inside the cabinet (the "AY" version also has the heaters transformer.) 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 (6K6G.) 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.

 

National Company, Inc. for U.S. Coast Guard

  Type R-116

The USCG Radio Receiver Type R-116 was built on contract TCG-33675 with the Order Number of CG-80265. This contract was issued before WWII began for the USA with a date of May 15, 1941. Interestingly, the R-116 chassis is similar to the later USN RAO chassis in that an extra RF amplifier section is added to the rear of the receiver. This contract dates the double-preselection upgrade for military National NC-100XA variants to pre-WWII and certainly must have affected the USN RAO evolution also. The R-116 uses eleven tubes as the RAO does however the circuit has several differences, uses different tubes and has several parts that aren't found in the USN RAO receivers.

The frequency coverage is different from the RAO with the R-116 covering 1.5mc to 27mc in six bands. This frequency coverage per band is spread out more than the NC-100XA or RAO receivers. The six bands required a different catacomb that was like National's NC-200 receiver that also used a six-band catacomb. The coil forms used in the catacomb are ceramic rather than National's normal coil form material (R-39.)

The catacomb band switch gear drive is very different in that the band switch knob shaft is coupled into a gearbox that rotates a shaft that goes back to the middle of the catacomb where the gear-rack is mounted to engage the pinion gear that's on the shaft. The RAO/NC-100XA had the rack mounted in the front of the catacomb driven directly by a short shaft and pinion gear from the band switch knob.
The front panel layout is significantly different with circular nomenclature plates (similar to the NC-200) used for all controls. The dial bezel is dramatically simplified when compared to the RAO. The R-116 doesn't have an S-meter. The Crystal Filter has just three positions, OFF-1-2. Additionally, the bar knob-operated dual toggle switches found on the NC-100XA/RAO were changed to single toggles on the R-116, each with its own nomenclature plate. The locations for the controls are quite different from the RAO. The band-in-use indicator is the same as the RAO receivers except for the six positions (Bands A thru F) rather than five positions. The dial is very similar to the RAO except for the bands' frequency scaling. Flanking the tuning knob are two logging charts. 

Note the four threaded holes in each corner of the panel. These were for an optional rack mount adapter that looks something like a picture frame with grab handles on the front. Rear support was provided with threaded holes in the bottom rear corners. It was also possible to use a cradle-type shock mount on these receivers (the cradle-type shock mount was also used on the RAO-2 thru 6 receivers.) The cabinet is very similar to the RAO-2 thru 6 in that it is made up of several pieces rather than the one-piece cabinets that were used on the RAO-7 and 9 receivers.

The R-116 lacks an internal power supply requiring that the receiver operates from a separate AC power supply (rack mount dual supply) or from a DC source such as batteries, motor-generator/battery combo or other types of shipboard power sources. Voltages required are 6 volts for the tube heaters and +230vdc for the B+. A four wire power cable exits the rear of the receiver. Audio outputs are 300Z and 600Z. Serial number on the R-116 shown is 46. Also reported is R-116 SN: 103.

Tubes Used - RF1-6K7, RF2-6K7, Mix-6K8, LO-6J5, IF1-6K7, IF2-6K7, Detector-6J5, AVC Amp/Rectifer-6SF7, BFO-6SJ7, 1stAF-6J5, AFOUT-6V6,

Components - Photo to the right shows the chassis of the R-116. The circuit below the tuning condenser is very similar to the NC-100XA or RAO with the exception of the oil filled bypass capacitors that are mounted to the chassis. Above the tuning condenser, where the AC power supply normally is on the RAO or NC-100XA, are several unusual components. The large box is an audio filter that can be switched in from the front panel. The left choke is also part of the filter. The transformer to the right of the choke is the audio output transformer. To the left of the two tubes in front of the filter is the Relay. It appears that this might be a remote speaker on/off relay.

 

U.S. Army Signal Corps

National Company, Inc. - NC-100ASD

National introduced a well-designed, direct-reading dial for their NC-100 series receivers in June, 1938. The "A" version dial had a mechanically articulated dial pointer that indicated the band in use when switching ranges and also included an S-meter as standard equipment. All of the other NC-100 features were retained, including the moving coil catacomb bandswitching, P-P audio, tone control, noise limiter (1940 models and later) and an optional crystal filter which was indicated by an "X" in the model designation. During WWII, the Signal Corps wanted a somewhat "militarized" version of the NC-100A. The receiver was designated as the NC-100ASD. It had special frequency coverage that included a medium wave band that tuned from 200kc up to 400kc. This required elimination of the AM BC band coverage since there was only room in the coil catacomb for five tuning ranges. The four higher frequency bands cover 1.2Mc to 30Mc. A single audio tube was provided, a 6V6, as was the 500 Z ohm output transformer that was to drive a matching loudspeaker that used an eight inch diameter Jensen with 500Z to 2.8Z ohm matching transformer. The loudspeaker cable was shielded to prevent RF pickup if the receiver was operated near transmitters. The probable contract number for the NC-100ASD is 9727-PHILA-43, dating from 1943. From reported serial numbers, the highest of which is 948, it appears that around 1000 NC-100ASD receivers were built. Shown in the photo is NC-100ASD sn: 194 with its correct 500Z ohm matching loud speaker.

After the war, the surplus market was certainly well-stocked with NC-100ASD receivers since apparently the Signal Corps didn't find much use for these receivers. Many ASDs were purchased surplus NOS at a price of $115 (1946 Newark Electric price) complete with matching speaker and manual. During the fifties and sixties, it was common to find the NC-100ASD used in many novice and "teenage radio amateur" ham shacks where economics dictated what sort of equipment was going to be in use. By then, ASDs were certainly "second-hand" status and priced quite reasonably. Performance was very good although QRM and lack of band spread probably limited most successful operation to 80M and 40M.

There was also an NC-100ASC version that was also designated as the AN/GRR-3. It appears that this version is similar to a militarized NC-100XA.

The Navy also wanted their own version of the NC-100A - it was designated as RAO - more details in Part 1 - Navy equipment.

 

asp1004.jpg (18383 bytes)ASP-1004 Receiver

Hammarlund Mfg. Co., Inc. - WWII Military Super-Pro 200 Series

The military had several different Super-Pro versions built during WWII. Most versions were nearly identical to their civilian counterparts in the SP-200 line. As with most military contracts at that time, other companies besides Hammarlund built the military Super-Pros (Howard Radio being the most commonly seen.) The most popular military versions were BC-779(civilian LX) covering 100 to 400kc and 2.5 to 20mc, BC-1004(civilian X) covering .54 to 20mc and BC-794(civilian SX) covering 1.2 to 40mc. There were other assigned model numbers also, probably depending on the end user of the particular contract, e.g., the R-129/U that covered 300kc up to 10mc. Also, a suffix was sometimes added to the BC designation indicating the type of power supply that went with each receiver. Hammarlund's advertising implied that many Super-Pro receivers were also used by our WWII Allies. Internally, there are only minor changes made to the civilian Super-Pro for military use. Many of the capacitors are combined into "bath-tub" type units that mount on the side wall of the chassis. Also, the wiring harness uses stranded wire and sometimes the solder joints are MFP'd. All of the WWII military Super-Pros use a steel front panel that is copper plated under whatever type of paint was used. Generally, the steel panels were painted with a smooth finish and the stamped nomenclature was white filled. Panel colors range from black or gray to shades of green-gray or blue-gray. There were several variations in the construction of the power supply also with most military versions using heavy-duty, over-size transformers and chokes along with oil-filled filter condensers. Some power supplies had dual primary or multiple tapped primary power transformers to allow operation on 230/115vac or a variety of ac voltages around 230/115vac. Designations are usually RA-74, RA-84 or RA-94.

The military Super-Pro receivers are great performers with fantastic audio, although most are rack-mount versions which is a configuration not usually favored by collectors. Additionally, many of the military models are in deplorable condition today due their lack of appeal to hams during the last several decades. The receivers not only require the normal electronic restoration but a serious cosmetic restoration, too. Only recently has the WWII Super Pro found an appreciative group of hams and collectors that find the build quality and superior performance to be unmatched by most of its contemporaries. Shown is a military ASP-1004 (same as BC-1004) - probably destined for Allied use (ASP=Allied Super Pro?,) with an original light greenish-gray panel, from the later part of WWII. Note the eight holes around the outer edge of the panel - these are on all military Super-Pro receivers and normally were there for mounting the chassis dust cover. However, sometimes these receivers were installed in a military desk-top cabinet designated CH-104-A with the dust cover removed and screws and nuts installed in these holes. Russia and Australia both built Super-Pro "knock-offs" during WWII, the KV-M from Russia and the AMR-200 built by Eclipse Radio in Australia.

The Signal Corps continued to support and use the SP-200 military versions post-WWI and well into the 1950s with upgrades to the the receivers and additions to the manual TM11-866. Improvement Kit MC-531 was a crystal oscillator kit that could be installed and would provide improved frequency stability with three selectable crystal controlled frequencies. There were other uses post-WWII, such as the AN/FRR-12, that utilized two modified BC-794 receivers in dual diversity with crystal controlled oscillators and crystal controlled BFO - all for reliable RTTY applications. The BC-794 receivers were professionally modified by Wickes Engineering and Construction Company in 1948. The MC-531 concept went on to be improved and incorporated into the standard design of the Hammarlund SP-600-JX receiver, which was introduced in 1950.

See "The Incredible Pre-War Super-Pro" web article for more details on military Super-Pro receivers, navigation link below.

 

the Hallicrafters, Inc. - Army-Navy AN/GRR-2

Most of the SX-28 and SX-28A receivers built for the war effort were standard Hallicrafters' production. In 1943, some SX-28s were built to a "heavy-duty" configuration that included a potted power transformer, dipped filter choke and audio output transformer and the return to the gear-driven bandspread tuning. These "heavy-duty" SX-28 receivers went to the Navy and the Signal Corps. Around April 1944, the SX-28A was introduced. It featured a series of improvements that had been incorporated into the very last of the SX-28 production. The major exception to these improvements was the High-Q Micro-set coils used in the receiver's new front-end and the installation of these coils warranted the designation change to "SX-28A." The U.S. Army Signal Corps and the U.S. Navy, wanted the SX-28A in the special "heavy-duty" build configuration and only these SX-28A receivers were given the designation of AN/GRR-2. The GRR-2 receivers are quite different from the standard SX-28A. The main differences are - the GRR-2 uses the same potted power transformer built by General Transformer Company, Korite dipped filter choke and audio output transformer and the gear-driven bandspread tuning system. This gear-driven bandspread been used in the earliest versions of the SX-28 receiver (the gear drive had been replaced with a dial string drive in mid-1941 SX-28 production.) The GRR-2 also has wax impregnated IF transformers and bandswitches, MFP fungicide coating on the solder joints and special heavy duty nylon insulated stranded hook-up wire in the harnesses. Additionally, the GRR-2 front panel was copper plated under the dark gray paint and the heavy-duty ball-end toggle switches have bakelite housings. The S-meter is a special unit that uses a bakelite case and is mounted using a special yoke system that mounts to the front panel with only two screws. All GRR-2 receivers were originally configured as rack mounted receivers and utilize a dust cover with hinged lid that provides ample protection whether the receiver is actually rack mounted or used as a table top receiver. The Signal Corps had its own manual for this receiver - TM-11-874 - with more detailed information than the standard SX-28A manual. The Signal Corps AN/GRR-2 shown is serial number HA-2703 and the fungicide dating is May 27, 1944. Only a few hundred AN/GRR-2 were produced.

 

National Co., Inc  -  HRO-W

The HRO-M was essentially a slightly updated version of the HRO Senior that was introduced in 1941. The HRO-M was produced for the military during most of WWII with many of the receivers being sent to England. During HRO-M production, the lack of any identification for the control function of the toggle switches that operated the B+ and the AVC had been corrected by installing metal function "rings" around the toggle switches. The HRO-M also replaced the "pull switch" used for the S-meter with a toggle switch. Many HRO-M receivers were equipped with a Marion Electric 0-1mA meter with a white scale that wasn't illuminated. In 1945, the HRO-M was given a major upgrade that changed all of the tubes to octal types with all tubes being the metal octal variety with the exception of the 6V6GT audio output tube. Most of the components under the chassis were changed to JAN types. Additionally, all of the coil sets were given new aluminum silk-screened ID plates that were mounted on the front panel of the coil set to provide a frequency chart and a logging chart. National identified this receiver as the HRO-5.

The U.S. Army Signal Corps wanted a few subtle changes and the HRO-5 model built for the Signal Corps was dubbed the HRO-W. The minor changes were a data plate that specifies that the receiver is an "HRO-W" along with extreme moisture and fungus proofing (MFP) of the receiver. Most HRO-5 and HRO-W receivers will have the following characteristics,...the S-meter will be a non-illuminated DC MA meter with a white 0 to 1mA scale made by Marion Electric, the same company that supplied the standard illuminated S-meter for the HRO receivers. The "ball-handle" toggle switch used to disable the S-meter on the HRO-M was replaced with a "bat-handle" toggle switch. Like most military HRO receivers, the coil sets supplied were the "J" series versions for the A, B, C and D coil sets. These were "general coverage" only - no bandspread function on the JA, JB, JC or JD coils. The additional coil sets that were supplied with the HRO-5/W were standard general coverage and brought the total coils sets supplied to nine. The additional coil sets were E, F, G, H and J sets which increased to coverage from 30mc down to 50kc with a small section not covered (430kc to 480kc) around the IF frequency (456kc.) The power supply was normally the Type 697 supply that had selectable primary voltages of 115vac or 230vac. Typically, the military opt'd for an audio output transformer to remove the B+ from the speaker terminals but the HRO-W doesn't follow this pattern and the audio output transformer is mounted on the speaker, if used. Generally, headsets were used for reception but this depended on the installation and ultimate use of the receiver.

Note the receiver shown in the photo above,...not only is the interior of the receiver given the MFP treatment but also the knobs and switches. The MFP's yellow lacquer base gives the PW-D micrometer dial a distinct "olive-drab" color and imparts the impression that the knob skirts are brass. There is a silk-screen label under the lid providing MFP treatment information which is date-stamped "JUL 29 1945."

 


BC-344-D Medium Wave Receiver - AC Operated

U.S. Army Signal Corps - BC-312, BC-314, BC-342, BC-344 Series - Various Contractors

The design of the BC-312, BC-314, BC-342 and the BC-344 receivers came from the U.S. Army Signal Corps in the late-thirties. Two versions operated on +14vdc utilizing an internal dynamotor (the BC-312 and BC-314) while the other two versions (BC-342 and BC-344) operated on 120vac utilizing an internal power supply unit, the RA-20. All versions of these receivers were stoutly built with rugged mechanical gear-driven tuning, robust wiring technique and made use of a steel chassis with extensive LO shielding utilizing a steel metal box. These receivers were built to "take a beating" and still function. While the overall size of the receivers is relatively small the weight is not - around 60 lbs - mainly due to the "all steel" construction of each receiver. Some aluminum is used (like the front panel) but the durability of the receivers is aided by the steel cabinet and chassis. All alignment adjustments have some kind of "tamper-proof" protection in the form of locking nuts, protective shields or plug covers. The BC-312, 314, 342 and 344 series of receivers were used extensively in ground applications from just before WWII up into the 1950s. The most common contractors were Farnsworth Television & Radio Corp. for both AC and DC operated receivers and RCA Manufacturing Co, Inc. for many of the early DC operated receivers.

The circuit is a nine-tube superheterodyne (ten tubes in the BC-342 and BC-344 which includes the 5W4 rectifier tube.) Two 6K7 RF amplifiers are used along with a separate 6C5 Local Oscillator and 6L7 Mixer tube. Two 6K7 IF amplifiers, a 6C5 BFO, a 6R7 duplex-diode triode for the Det/AVC/1st AF function and a 6F6 audio output tube complete the tube line up. Frequency coverage is from 1500kc to 18000kc in six tuning ranges for the BC-312 and BC-342. The BC-314 and BC-344 are medium wave receivers and cover 150kc to 1500kc in four tuning ranges. The BC-312 and BC-314 are operated on 12-14vdc (BC-312-NX version 24-28vdc op) and were intended for vehicular use, which could include trucks, cars, jeeps or tanks. The BC-342 and BC-344 included the RA-20 AC power pack allowing the receivers to operate on 110-120vac with the intended set-up being a fixed station inside a building but mobile stations were possible powered by a portable AC generator. The huge "trunk" connector protruding out of the front panel allows power input on DC versions (or filament voltage access on AC models,) telegraph key input, PTT and microphone routing, remote stand-by (in DC versions,) audio outputs and antenna relay function for interfacing with transmitters and other equipment. All versions of the BC-342 have a Crystal Filter while the DC operated versions will have a DIAL LIGHT control. Early versions of the receivers will have a wire dial index and a fixed 4000Z ohm audio output. All later versions have a plastic dial index and selectable audio output impedance of either 250 ohms Z or 4K ohms Z. Some versions allow access to the 1st AF output for earphone operation while the typical BC-344 set-up has both phones and speaker outputs tied together from the audio output transformer.

The receiver shown in the photo above is the BC-344-D built by Farnsworth Television & Radio Corp. This is an AC operated, medium wave receiver. Note that there isn't a Crystal Filter provided on this version and, since it's AC operated, there is no DIAL LIGHT control.

RESTORATION NOTES

Front Panel Removal:   If you are planning to restore one of the BC-312/342 or BC-314/344 receivers, be aware that the mechanical design does not consider ease of maintenance beyond changing tubes and routine alignment. Any of the receivers will be very difficult to disassemble, requiring the unsoldering of several connections and disassembly of other mechanical parts just to remove the front panel.

Mechanically, the Fast Tuning gear and flanged shaft have to be "un-pinned" so the gear and flanged shaft can be separated and removed from the front panel and interior gear panel to allow a front panel dismounting. Also, the front panel "trunk" connector wires must all be unsoldered to dismount the front panel and, additionally, there are some screws mounted to be backside of the front panel that must be removed. Even the two fuse holders must be unsoldered and removed before the front panel can be dismounted. In all, any work involving front panel removal is arduous.

The "phones" audio transformer is not accessible without front panel removal and removal of the BFO assembly. Dismounting any of the smaller assemblies is time consuming and usually requires unsoldering joints where the wire was wrapped one and a half turns before it was soldered. Additionally, there are many different length screws and standoffs that have specific locations so care must be observed during disassembly to keep everything identified for proper reassembly. Front panel removal is sure to result in several large piles of sorted screws and other parts along with several drawings and notes before reassembly can begin.


Shown in the photo above is the BC-312-N. This receiver has an onboard dynamotor that operates on +14vdc to provide B+ to the receiver. The tubes are standard 6 volt metal octals that are wired in series-parallel. There is no Crystal Filter provided but, since the BC-312 is DC operated, there is a DIAL LIGHT control. The DC voltage input is via the front panel trunk connector.

Other Problems:  Sometimes the OFF-MVC-AVC switch will have contact problems the prevent the receiver from powering up. The switch is a custom-built, stacked four level assembly that has no replacement other than another original switch. It's easy to access the power section of this switch since that section is not enclosed. Rather, it is protected by a fiber board cover that can easily be bent to access the contacts. Careful cleaning and readjustment of the sliding arm and contact point can usually get the switch working again. It seems that the contact problems are more due to oxidation and dirt since these two contacts are not sealed.

A common problem with later BC-312 et al receivers is lack of transparency and warping of the plastic dial index. Since the dial index assembly is mounted to the backside of the front panel with eight screws that are not accessible because of the dial assembly and mask, the front panel must be dismounted to replace this problem-prone part. The plastic is riveted to the metal bezel so removal of the deformed original will require drilling out the rivets. Making a new plastic dial index is fairly easy using thin plastic salvaged from "cheap" picture frames. This material is flexible but has some thickness to it and is fairly close to the original material. Scribe an index line and fill the line with white Artist's Acrylic paint, wiping off any excess so only the index has paint in it. Mount the new plastic index by either using rivets, fake rivets made from 2-56 screws and nuts or by epoxy'ing the new piece in place. Note in the photo of the BC-312 above that the dial index plastic has shrunk and warped to the point where the dial mask nomenclature can be seen over the .25" gap at the top of the dial cover. This is a "front panel off" operation to replace this piece.

IMPORTANT REASSEMBLY NOTES: When reinstalling the front panel screws it will be noted that all of the 6-32 screws are the same length but there are three different lengths of 4-40 screws. There are two "short" 4-40 that must be installed in the correct location otherwise the dial mask will be scratched when the band switch is operated. One "short" 4-40 is installed near the band switch knob and near the word "CHANGE" in the band switch nomenclature. The other "short" 4-40 is installed near the lower-left corner screw of the data plate. The four "long" 4-40 screws are for mounting the wire clamps that are made from fiber blocks. The remaining 4-40 screws are all the same length.

On the AC operated models, the RA-20 power supply uses a dual electrolytic filter capacitor. This is not an oil-filled paper dielectric capacitor as used in other military gear. The RA-20 filter capacitors are often bad and require replacement. It's easy to use the original can to house the modern replacement electrolytic capacitors. The RA-20 is very compact and densely packed. There's no room for anything other than the original parts. So, stuffing the replacement electrolytics inside the original can is the good solution that makes use of the available mounting bracket and hardware.

The photo right is a Farnsworth-built BC-342-N. This is an early version of the "N" with the wire dial fiducial, non-selectable audio output Z (fixed 4K ohms) and the typical Signal Corps hand-written upgrade nomenclature above the ID tag. Note that this version does have a Crystal Filter provided (control is marked CRYSTAL PHASING.) 

Final Notes: Certainly the difficulty of performing any serious repair work or modifications has "saved" many of the BC-312, '314, '342, '344 receivers. Most of this family of receivers will be found without extensive modifications. Many are found in "all original" condition. Most receivers were heavily coated with MFP and this also has prevented the "faint-of-heart" from performing any serious rework to the receivers. Even the alignments are usually close because all adjustments were "locked" with various lock-nuts, plug covers or cover-shields. Quite different from the BC-348 receivers that were easy to work on and thus are always found with some modifications to originality. Sometimes you might find a BC-312 that has the RA-20 installed but this is easy to convert back to a stock, DC operated BC-312 as long as you can find the correct dynamotor, which isn't difficult.

All of this laborious restoration work will be rewarded as the BC-312/314/342/344 receivers are excellent performers with great sensitivity and plenty of audio when driving a matched speaker. The stock LS-3 is a good match for the 4K impedance of the BC-312 et al receivers.

 

Signal Corps U.S. Army  -  Panoramic Adapter BC-1031-C

Contractor: New London Instrument Co.

The Signal Corps US Army BC-1031-C was designed for 455kc operation. The earlier versions of the BC-1031 were built by Panoramic Radio Corp. and are black wrinkle finish with "toilet seat" covers over the adjustments. The "C" version was built by New London Instrument Co. and had a smooth finish satin black paint finish and featured a "sliding cover" (with thumb screw lock) to access the adjustments. The SC always had their own spelling,...note the BC-1031-C is a Panoramic Adapter ("e" instead of "o.") Interestingly, the SC decided to spell it "Adaptor" in the manuals.

These early types of panadaptors were not really designed for in-depth analyzing the characteristics of a signal. The intent was to use the panadaptors to easily and quickly spot signals that were outside the surveillance receiver's IF input passband (mixer output.) Once seen, the operator could then tune to the signal (which was seen on the panadaptor screen as the "peak" traveling across the graduated scale to the center at which point the signal is heard in the receiver.) The operator could generally tell what kind of signal it was from the display - either CW or AM. Relative signal amplitudes could be compared and specific signal frequency could be estimated using the graduated scale. Odd characteristics involving the type and level of modulation would be apparent. The sweep width was about 100kc.

There were also VHF panadaptors such as the BC-1032 Series. These units had IF inputs of approximately 5.2mc and generally would sweep around 1000kc bandwidth. They are very similar in appearance to the BC-1031.

 

Special Purpose Receivers for Various End Users

RCA's AR-88 Series was in the preliminary design phase when WWII broke out in Europe. It was rushed to completion so it could be supplied to England where it was used primarily for intercept. The AR-88 was also supplied to other WWII Allies with very few receivers actually remaining in the USA during the war. When the AR-88s were being exported on Lend-Lease, RCA made it clear they didn't want the receivers returned to the USA after the war. Consequently, many were destroyed after the war ended. But, many have survived in the UK and in Europe. Almost all early versions are NOT in the USA. Most USA AR-88 receivers are from late in WWII or are post-war production. Certainly the majority of AR-88 versions were produced during WWII but the significantly reduced post-war production continued on until the early-1950s.


RCA AR-88D ca.1944

Radio Corporation of America  -  AR-88 Series

     includes: AR-88D, AR-88LF, CR-88, CR-91, SC-88, R-320/FRC - also Triple Diversity Receivers DR-89, RDM and OA-58A/FRC 

RCA's most successful communications receiver was the AR-88. Designed in 1940-41 by Lester Fowler and George Blaker (and rushed into production because of WWII requirements) the AR-88 was a 14 tube superheterodyne that covered .54 to 32MC in six tuning ranges and featured incredible sensitivity (even up to 10 meters), excellent stability and high fidelity audio (from a single 6K6.) Most of the production was sent to England, Russia or other Allies during WWII using Lend-Lease which accounts for the relative scarcity of the early versions of the receiver in the USA. The AR-88 was used extensively in Great Britain during WWII for various purposes. RCA and Radio Marine Corp.of America also used the AR-88 and its variants in their own installations for various purposes. Even the US Military used some of the later AR-88 variations in their installations. Contrary to some published estimates of unbelievably high production levels in excess of 100,000 units, serial number analysis seems to indicate that around 30,000 AR-88 series receivers were built between 1941 and 1953. Most of the production quantity went to our Allies during WWII. Post-WWII production was probably less than 4000 receivers. It's common to hear stories of post-war destruction of AR-88s by our Allies however most receivers continued to be used by our various Allies (some of which didn't remain Allies) after the war. None were ever returned and few were ever paid for (return, destroy or buy for ten cents on the dollar was part of the Lend Lease arrangement.)


photo above: Camden-built CR-91 ca:1945 with MI-8303D loudspeaker

The AR-88 series receivers use three stages of 455kc IF amplification with stagger-tuned IF transformers. Two under-coupled IF transformers and two over-coupled IF transformers are utilized when the receiver is operated in the "BROAD" selectivity position. To assure that the passband is symmetrical usually requires a sweep generator and oscilloscope for proper alignment. However, if fidelity is not an issue, there is a procedure to align the IF section using just a VTVM but the results are usually not as good as the sweep method. There are five steps of selectivity with position 1 and 2 being rather broad for good fidelity while positions 3,4 and 5 use the crystal filter for increasingly narrow bandwidth. A Noise Limiter and a Tone control were provided. The standard table top version was designated as AR-88D and it sometimes had a Carrier Level meter incorporated into the circuit however many AR-88D receivers didn't have CL meters installed due to a shortage of meters that occurred during WWII. The wiring for the meter was sometimes included in the harness for future installation of a CL meter, if they became available. Generally, the wires for the meter connection are bolted to the lamp bracket behind the receiver's illuminated ID window. Early in WWII, some of the Allies required receivers that covered MF frequencies and the AR-88LF was created, covering 70kc to 550kc and 1.5mc to 30mc. The first 3000 or so AR-88LFs used different power transformers and different audio output transformers from the AR-88D. The IF was at 735kc to allow complete coverage in the 400kc to 500kc range. All AR-88LFs were built at the RCA plant in Montreal.

Many of the AR-88 receivers were used in RCA Triple Diversity Receivers like the DR-89 - a seven foot tall rack loaded with three AR-88F receivers and all of the auxiliary equipment necessary for professional diversity reception. The Navy designation for the DR-89 was RDM. The Diversity AR-88F receivers did not have CL meters installed because the Diode Load current output from each receiver was routed to the Tone Keyer terminal board but the actual three Output Level meters were mounted in the Monitoring Unit Panel of the DR-89/RDM rack. All Diversity AR-88 receivers (and their variations) that were used in RCA Triple Diversity Receivers will have a "DIVERSITY IF GAIN" control on the front panel. This provided a method of adjustment for balancing each of the receiver's output for equal diversity effect (using the actual desired signal) even if the receivers/antennas were not exactly identical in their performance. The U.S. Army Signal Corps had their versions of the RCA Triple Diversity DR-89 with the Signal Corps ID of OA-58A/FRC. The Army SC diversity set-ups used a slightly different, upgraded receiver, the SC-88.

 

The AR-88D, CR-91 and some of the other variants that weren't specifically for RCA diversity racks didn't have the "DIVERSITY IF GAIN" control and were usually installed in a table cabinet although this wasn't always the case. Note that in the case of the AR-88D, the "D" does not indicate a "diversity" receiver, only the AR-88F, CR-88A and SC-88 are true diversity models of the '88 receiver. A matching speaker was available for all table models. The CR-91 was the version of the AR-88LF that was built in at Camden, NJ during WWII while the AR-88LF itself was built in Montreal during WWII. Very few Camden CR-91 receivers were produced. The majority of so-called CR-91s that turn up today are actually CR-91A versions built post-WWII in Montreal. The CR-91A has a front panel Phasing control for the Crystal Filter. The AR-88 series of receivers were produced from 1941 up into the early fifties. The CR-88B was the last of the AR-88 series, available from 1951 up to 1953. The CR-88B features push-pull audio, two position tone switch, dial masking, crystal calibrator, 15 tubes and a three position selectivity switch.

The AR-88 series of receivers are well known for their amazing performance with fabulous audio reproduction and great reliability. Unfortunately, a great many AR-88s led a hard life and then were stored in poor environmental conditions that nowadays results in the receivers being found in "rough" condition with missing shields, missing parts and usually other more serious problems even though the receiver may still function. Many receivers are found as victims of careless or incompetent repairs or needless "hamster" modifications. A "well-cared for," original AR-88 that has not been modified will usually function quite well but if it has been carefully and correctly rebuilt. Then, if aligned (using the sweep method for the IF) it will have tremendous sensitivity and flawless audio reproduction. The front panel adjustable Crystal Phasing used on the later versions allows the user to not only adjust the selectivity of the receiver but also to use the Crystal Filter to reduce or eliminate heterodynes.


photo above: CR-88A version from 1947 in RCA "umber"



1950 Signal Corps R-320/FRC, aka RCA SC-88, part of OA-58A/FRC
 

The AR-88 was one of the first receivers that was designated as a "continuous bandspread" receiver due to its substantial gear reduction but its tuning accuracy relies on the logging scale for precise reset ability. The direct frequency readout resolution is vague. The AR-88 receivers are stoutly built using all steel construction and they are heavy, weighing in at nearly 100 lbs when installed in the cabinet. 

Shown in the photo to the left is the SC-88 (Signal Corps designation R-320/FRC, SN 214, used in OA-58A/FRC diversity receivers) one of the later of the AR-88 versions from 1950, featuring "band-in-use" masking and the crystal phasing control on the front panel (the AR-88's is internally adjusted.) Since the SC-88 was specifically built for the Signal Corps' diversity racks, these receivers are rack mount configuration only and have the "DIVERSITY IF GAIN" control on the front panel. The total production of SC-88 receivers was quite small with estimates usually being around 300 receivers built. Although the SC-88 appears similar to the earlier AR-88 series, many changes took place inside which moved the locations and designations of the front end alignment adjustments. Using an AR-88 manual for aligning an SC-88 will not provide accurate information. The proper manual for the SC-88 is TM11-899. 

Shown in the top photo is the AR-88D from WWII. The first inset photo shows the early version of the CR-91, a receiver that is very similar to the AR-88 but with a frequency coverage of 70kc up to 550kc in the first two bands and then 1.5mc to 30mc in the remaining four bands. The CR-91 uses a different IF frequency of 735kc to allow continuous coverage in the LF and MF spectrum. Additionally, the audio output tube was changed from the 6K6 to a 6V6. The slightly different (wider) IF bandwidths are a product of the higher IF frequency. The CR-91 version was introduced during the last part of WWII with these receivers built at Camden and having the non-adjustable crystal filter phasing and a black wrinkle finish panel.

The later CR-91A essentially took the place of the AR-88LF with all manufacturing at the RCA plant in Montreal. The CR-91A was an updated version that has the front panel crystal filter phasing control and a smooth gray finish on the front panel. Most early CR-91 receivers were in cabinets and were probably used for surveillance or LF/MF communications onboard ships (some CR-91 manuals warn about excessive LO radiation on the antenna if the A2-G link is removed.) Shown in the second inset photo is the 1947 CR-88A. These receivers were generally for the later versions of the DR-89 and RDM Triple Diversity Receivers but sometimes they are found as individual receivers that were used for a multitude of purposes. This example of the CR-88A is installed in a matching RCA cabinet. 

For the ultimate information source on the AR-88, including more history, the triple-diversity receivers, serial number analysis, how to do sweep IF alignment, restoration hints and performance details go to our web article "RCA's Amazing AR-88 Receivers" - Use the Home/Index below for navigation.

 

WWII Radio Test Equipment

 

U.S. Navy  -  Model LR-1

Combined Heterodyne Frequency Meter and
Crystal Controlled Calibrator Equipment

General Radio Company


The General Radio LR-1 is the "Rolls-Royce" of  Frequency Meters. With 21 tubes and weighing in at around 120 lbs, just in shear size, it dominates any radio landscape it inhabits. The LR-1 has just about everything GR could think of to put into a single box, albeit a very large box measuring in at 23" H x 18" W x 17.5" D. The circuit allowed for extremely accurate frequency measurement, whether measuring an incoming RF signal (transmitter) or determining a correct frequency for radio reception.

GR provided a very rapid and extremely easy method to measure frequency that allowed the user to just "dial in" the Heterodyne Frequency Meter (HFM) and directly read the frequency on the tuning dial scale. GR also provided a more thorough and extremely accurate method of measurement that could be used when needed. This accurate method used a crystal-controlled 100kc calibration oscillator that provided either a 10kc or 20kc signals by way of multivibrator circuits to heterodyne with the HFM's output that would be tuned to the nearest calibration point that was lower than the frequency to be measured. Then, using the Interpolator, these heterodyne beat notes could be measured with the large "arced" meter at the center-top of the panel (the meter is calibrated in kilocycles.) With internal filtering, each 10kc beat note would only actually respond up to around 5kc before the next heterodyne beat note would begin to "tune in." Each 5kc frequency change would produce either an increasing frequency or decreasing frequency as each heterodyne beat note was tuned through. The Interpolator was calibrated to measure the frequency of the beat notes and then drive the meter to the correct frequency indication (since a lower calibration "set" frequency was used, that provided an increasing frequency beat note that then caused an increasing meter movement.) The frequency indicated on the meter in kilocycles would then have to be added to the frequency that the HFM dial was set to. For example, if the HFM dial was set to a calibration point of 10,510kc (heterodyne heard in the 'phones) then the HFM dial tuned until the heterodyne is heard in the receiver's output, then, if the Interpolator Meter indicated 3.6kc the measured frequency would be 10,513.60kc. This method allowed for extremely accurate measurements since each calibration point and associated beat note was <5kc from the frequency that the HFM was set to. Above 15mc, 20kc is used for the calibration frequency.

Other circuits provided a Detector-Audio Amplifier to drive headsets with either local or remote outputs available. The Detector-Audio Amplifier also provided sufficient drive for the Interpolator. Tubes used are nine type 76 tubes, one type 75, one type 6SK7, two type 6C6, two type 884, four VR-105, one type 83 and one type 84 are used in the LR-1. The LR-1 operates on 115vac.

The serial number on the LR-1 shown in the photo above-right is 1081. The contract date shown on the data plate is 7 April 1941 which is actually before the US became involved in WWII. However, the USN "acceptance tag" date is 1-6-44 which indicates that the LR-1s were certainly built during WWII. These "over-the-top" HFMs were typically set-up onboard ship along with the USN Type RBA longwave receivers and the RBB and RBC medium and shortwave receivers. They were also used at shore stations where accurate frequency measurements were necessary for both transmitters and receivers.

 

Heterodyne Frequency Meters

US Navy - LM Series      US Army Signal Corps - BC-221 Series
 

Heterodyne Frequency Meters provided a method of accurately measuring either a transmitted frequency or a received frequency of operating radio equipment. All receiver dials, prior to WWII, were vague in accuracy and didn't provide a precise readout of where exactly in the RF spectrum the receiver was tuned. The heterodyne frequency meter used a tunable oscillator to produce a frequency-accurate signal that could be "tuned" to the receiver's tuned frequency thus providing a heterodyne that provided the operator an accurate measurement of the receiver tuned frequency. All USN LM freq-meters provide an option of either a CW signal or a modulated (400Hz) output (for "MCW" receivers.)  U.S. Army Signal Corps models only provide CW output.

To measure a transmitter's output frequency required the user to put on the headset of the Freq-Meter (the headset must be plugged in to power up the BC-221 series.) The transmitter frequency is then tuned-in with the Freq-Meter acting as a receiver and, as the transmitter frequency is tuned-in, a heterodyne is heard in the headset. Zero-beat will be the transmitter frequency (or a harmonic there of.) All Freq-Meters will have a calibration book that is for the particular unit as all tuning dials are a micrometer type device in order to provide the necessary accuracy. Specific calibration frequencies are shown in the book that allow tuning to the built-in 1000kc crystal calibrator which then, using the "Corrector" control, allows the user to set-up for maximum accuracy.

Modern digital frequency counters have replaced the old Freq-Meter (as has synthesized tuning on transmitters and receivers) providing extremely accurate read-outs. However, it's fun to go through the methodology of using a Freq-Meter and get a feel for what was the "standard" for accurate frequency measurement - pre-digital frequency counters. You might be surprised at just how accurate the old BC-221 or Navy LMs are (with careful set-up, better than 1.0kc accuracy is normal.)

photo right - USN LM-18 and power supply. The power supply uses a type-84 rectifier tube and oil-filled paper capacitors as filters. The switches COMP 1 and COMP 2 allow the user to set the AC operating voltage with both switches up if AC is 110vac or less, switch 1 down and 2 up if AC is 120vac or higher and 1 up and 2 down is AC is between 110vac and 120vac. The interconnecting cable uses five-pin connectors although only four pins are used. The stock cable was nine feet long. The AC power connector is the same style connector but only three pins are provided. The LM-18 uses three tubes, a 77 heterodyne oscillator, a 6A7 crystal oscillator-detector and a 76 modulator-audio amplifier. The calibration book has metal covers and slides into a holder below the LM. Both the LM and the PS have shock-mount bases. Behind the metal protection dome on the power supply is a 120vac 6W pilot lamp (actually, an indicator lamp.) When original and complete, the serial numbers on the LM, the calibration book and the PS will all match. This LM-18, calibration book and PS is SN 222.

The upper left-most photo shows the USN LM-21 with its companion AC power supply. This unit was rebuilt at the Mare Island Naval Shipyard in the 1960s. It is complete with its original cables (not shown in photo.) Note the vernier "arm" on the CORRECTOR control. This modification is actually listed in the original Mare Island rework papers that came with this LM.

The photo upper middle shows the US Army Signal Corps BC-221-J built by Zenith Radio Corp. during WWII. Like many BC-221s this unit has an added "homebrew" AC power supply in the battery storage area. The red pilot lamp is also not original. Note on the BC versions - no MODULATION option. 

Shown in the photo upper right is the US Army Signal Corps BC-221-AK built by Philco. This unit is installed in the olive drab painted wooden box with canvas covers. The Antenna and Ground connections were placed on the front panel on these versions. Also, the controls are relocated on the panel with the Crystal and Freq Band controls slightly changed in their functions.

The photo left shows the "official" AC power supply available (with regulated B+) for the BC-221 designated the RA-133-A. The power supply will fit into the battery compartment although some of the battery retainers might have to be removed. A short cable connects to the BC-221 A+, B+ and A-/B- terminals in the battery compartment  The AC power cable has an in-line switch and pilot lamp. All BC-221s were originally battery operated because they were used in the field or in aircraft. Since the RA-133-A is fairly hard to find, many BC-221s have had "homebrew" power supplies installed into the battery pack area of the unit. Most of these homebrew types of supplies don't have regulated B+.

 

U.S. Navy  -  LP-5  RF Standard Signal Generator
CFD-60006-A - Signal Generator Unit
CFD-20080-A - Rectifier Unit

Federal Manufacturing and Engineering Corp.


The LP-5 RF Signal Generator (CFD-60006-A) is a "military contact" reconfiguration of the famous pre-war General Radio Company Type 605-B Standard Signal Generator. The LP-5 was built during WWII by contactor Federal Manufacturing and Engineering Corporation, a company that was mainly known for photographic equipment such as cameras and enlargers. As with many "contractor-built" units for WWII use, the LP-5 uses many primary source OEM parts and components in its construction. In this case, parts and components from General Radio Company. The same build method was used for the WWII Wells-Gardner-built RAO receivers that used many National Company parts in their construction.

The LP-5 was repackaged as a semi-portable RF generator built into a heavy-duty aluminum case. It can be operated from either its separate 115vac operated rectifier power unit or from a battery set-up that provides +200vdc for the "B" supply and +6vdc at 1.7A for the "A" supply.  

Although the pre-war GR version mounted its PI-605 power unit in the same cabinet as the oscillator unit, the LP-5 set-up utilizes a completely separate rectifier unit, the CFD-20080-A, that is connected to the oscillator unit via a power cable. The CFD-60006-A's metal case had a screw-mounted cover that had the dummy antenna, a 10:1 attenuator and cables clip-mounted on the inside (these covers are almost always missing from units found today.)    >>>

>>>   The frequency coverage of the LP-5 was from 9.5kc up to 30.0mc in seven tuning ranges. An additional tuning range allowed the frequency coverage to be extended from 30mc up to 50.0mc although with reduced accuracy in frequency readout and reduced output levels. The internal modulator provides up to about 50% modulation (fixed 1000 cycle sine wave) with very little distortion but higher mod levels, although available, will increase the distortion significantly. External modulation is also an option. The LP-5 has a built-in VTVM that measures the RF output level, although not directly. The user adjusts the output level to a reference line on the meter and then the output attenuator scale is accurate when referenced to the multiplier setting. Modulation level is read directly on the meter scale. A constant "one volt" RF output is provided at the upper coaxial fitting to allow for various types of monitoring or measurement. The lower coaxial fitting is the attenuator output that is normally used for calibration purposes. The coaxial fitting use the standard Navy "snap in" coaxial plug.

The LP-5 uses five tubes, 76 RF Osc, 89 Separator, 76 Modulation Osc, 84 Modulation VTVM rectifier and a 955 RF Carrier VTVM. The rectifier unit uses an 84 tube which brings the total tube count to six.

 

Although the General Radio 805C is actually a post-WWII piece of equipment it certainly evokes the wartime era perfectly - immense in size and weight along with being expensive beyond belief. It was the post-WWII replacement for the General Radio 605-B on which the LP-5 (above) was based.

General Radio Company

Type No. 805-C  Standard Signal Generator

The enormous General Radio 805-C is probably one of the largest Standard RF Signal Generators that was ever produced. It's 30" long by 16" high and 11" deep. Weight is over 100 lbs. The tuning dial is 8" in diameter. 12 tubes total which includes the Amperite 3-4 ballast tube. The RF Oscillator and the RF Output tubes are usually metal 6L6 tubes but this particular 805-C was equipped with 1614 tubes instead. The 1614 tubes are 20W plate dissipation, heavy-duty industrial versions of the 6L6 metal tube. These weren't end-user substitutions either - this 805-C has the General Radio "1614" tube identification tags installed. The RF Output is modulated by a 6L6. The power supply is electronically regulated using a pair of 2A3 tubes along with a 0D3 regulator tube. Two rotating turrets have the individual band coils mounted to them with the Oscillator turret and the Output turret rotating simultaneously with the band switching action. The entire RF box is fully shielded. Alignment can be performed with all shielding in place by way of the alignment holes in the front panel (they have metal hole plugs installed normally.) Frequency coverage is from 16.0 KC up to 50.0 MC. Modulation is selectable 400~ or 1000~ or External. The Output Attenuator allows signal outputs to be reduced to < 1.0V while full output is measured in volts (2 vrms FS on the meter.) The Attenuator is also entirely shielded in its own metal box and has a 6AL5 tube inside that is part of the Output VTVM circuit. Metering allows measuring percentage of modulation and RMS output level. These massive, behemoth signal generators were the industry standard from just after WWII up to around the early-1960s. The 1951 selling price from GR was $1450 and by 1961 it had escalated to an incredible $1975.

 

Weston Electrical Instrument Company
for the U.S. Navy

Model OQ-2  Vacuum Tube Analyzer (Weston Model 788)

Weston supplied their Model 788 as the "OQ" to the Navy during WWII. It's nearly two feet tall and weighs 35 lbs. The contract is No. NX55/3-13581 and dates from 1942. The OQ was used at radio repair depots and in areas were radio design and testing were performed by the USN. The lid slides off of the hinges if desired. Inside the compartment at the top of the OQ are 12 patch cords and the AC power cord. All connections between the tube socket panel and the analyzer/power supply/meter panel are accomplished using the patch cords. The roll-chart assumes the operator knows the tube socket pin-outs but if needed all tube pin-out data is contained in the manual. Once the operator knows what the tube pin-outs are, the patch cords are inserted from pin jack receptacles marked 1 thru 8 on the socket panel and connected to the various pin jack receptacles marked to identify each tube element on the meter panel. The tube is then inserted into the proper socket, 4-pin, 5-pin, octal, etc. The tube heater voltage is roughly set by control A and adjusted using the fine adjustment to the correct voltage as read on the left-side meter. Control B should be set to Shorts Test initially. Control C is a variable pot and is set per the roll chart data. Control D is a multi-position switch that is also set per the roll chart data. These two controls (C and D) select the correct voltage divider resistors for proper tube element voltages. The Plate Voltage is an adjustable control that is set to read "100" on the right-side meter. Meter Reset should be fully CCW to start. First the tube is tested for shorts watching the neon lamp. If no shorts are indicated then the switch is set to TEST. Now the arced center meter will read some value of plate current. Using the Meter Reset control the plate current reading is adjusted to zero. Now the Gm TEST switch is actuated and the test value mutual-conductance percentage will read on the arced meter. Diodes and rectifiers only are emission tested. The OQ-2 is not a "quick" or "easy to use" tester and requires some extra data not found on the roll chart (all required data is in the manual however.) The OQ-2 is quite a visually impressive unit that's a lot of fun to use.

 
 
 

WWII Navy Gear - Part 1            WWII Airborne Radio Gear - Part 2             WWII Ally Comm Gear - Part 4             Home Index

 

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