Radio Boulevard
Western Historic Radio Museum


WHRM Radio Photo Gallery

 WWII Communications Equipment  

U.S. Navy Shipboard Entertainment Radios
U.S. Army Signal Corps Radio Gear
US Army Air Force Airborne Radio Gear
 and WWII Allied Radio Equipment 

 

PART 2

 

U.S. Navy Shipboard and Shore Entertainment Receivers

SLR-F Receiver with BFO

E. H. Scott Radio Laboratories, Inc.  -  SLR Series, RBO Series

During WWII, Scott Radio Laboratories was contracted to design and build a type of military marine entertainment receiver that had very low Local Oscillator radiation or leakage to the antenna system. Scott advertising of the time indicated that the Navy was concerned with the possibility that enemy submarines could tune in a superheterodyne receiver LO signal and determine a ship's position with direction finding equipment. The Scott ads further stated that enemy DF equipment was sensitive enough to detect LO signals up to 100 miles away. While this all may have been theoretically true, the primary reason for the installation of low radiating receivers onboard ships is that any receiver has to operate in the presence of the several other receivers, transmitters and sometimes radar equipment that would also be in use on the ship. None of the receivers can cause interference with ship equipment and they must be able to perform their function without interference from other ship equipment. The USN specification was "less than 400 pico watts" was to appear on the antenna from local oscillator leakage. The "Scott Low Radiation" Receiver, or SLR, was built to operate in such a shipboard environment with no interference. The Scott SLR receivers tuned the standard AM Broadcast band and two bandspreaded Shortwave bands. They were designed as a stand-alone receiver capable of high quality reception and wide range audio reproduction via its powerful push-pull 6V6 output stage.

The multi-tap output transformer allowed matching to virtually any impedance that might be encountered with 600 ohms being the most commonly encountered. The receiver's output could be distributed throughout the ship via the 600 ohm line or it might be matched to the distribution amplifier for the ship's audio system. Each ship had different requirements and the Scott was designed to work with just about any of the ship speaker-audio systems. Single preselection, two IF amplifers and a Noise Limiter were included. A BFO was also included in case the receiver had to double as a communications receiver. When in the C.W. position, the AVC is disabled and the Volume control actually controls the RF-IF gain so the signal to BFO injection ratio is correct. A cathode-ray "tuning eye" tube was also included in the SLR version.

Not all versions of the SLR receiver will be equipped with a BFO. If the BFO is not installed then the data plate is mounted where the CW OSC control was.

 

 

photo left:  Scott SLR-12-B. This version doesn't have a BFO. This SLR is complete but awaiting restoration.

Scott also built the RBO receiver, a similar looking set but without the push-pull audio and without a BFO. Parallel rectifiers are used in the RBO and sometimes the receiver is seen with a drop-down dial cover - a hinged metal piece that can be raised up to entirely cover the illuminated dial. The RBO generally was used for local entertainment within a limited space (one room) since the single 6V6 audio output didn't provide enough power to drive the the ship's 600 ohm line directly (it could run the distribution amp though.)

Both the SLR and the RBO receivers were installed in a very large metal cabinet that was shock-mounted to a substantial base mount.

Scott built many different versions of these high quality "entertainment" receivers. The receivers were installed not only on U.S. Navy ships but also merchant ships, tankers, transports and other types of American vessels.

 

 

 

photo right: Scott RBO-2. This version has single-ended audio and no BFO. This particular RBO-2 was rebuilt by Mare Island Naval Shipyard in the early 1950s. The panel and cabinet were repainted light grayish-cream color and the nomenclature masked to preserve readability. The metal data plate located under the "eye-tube" is the Mare Island "rebuild" tag.

 

Scott Radio Laboratories, Inc. - SLRM Marine Receiver

The SLRM is a twelve-tube shipboard receiver that operates on 115 volts AC or DC. The construction is unusual in that aluminum is used for chassis, the shielding and the cabinet. This reduces the receiver's weight significantly - weight is around 50 lbs. Single pre-selection is used with two IF stages. An ineffective BFO and a clipper-type Noise Limiter are provided. Selectable bandwidths are available. The RF gain is controlled by the AVC when MOD bandwidths are selected but the RF gain becomes a manual control if CW is selected. Frequency coverage from .54mc up to 18mc. Push-pull 25L6 tubes for the audio output. The 1629 "eye tube" only operates when AVC is controlling the receiver sensitivity in MOD modes. In CW, the 1629 will remain "on" but the "shadow" will not respond to signals since the AVC is disabled. The panel speaker is 5" in diameter but there is a multi-impedance-taps output transformer for external loads. The panel speaker can be turned off if an external speaker is used. Onboard the ship, the audio output would have been connected to distribute the receiver output as necessary.

Performance is quite good for AM signals. In the HF bandwidth AM BC signals or strong SW BC signals sound great if a large diameter, matched external speaker is used. The SLRM was primarily an entertainment receiver, not a communication receiver.

On the downside,...there will be many problems encountered when operating the SLRM. Images become very apparent around 15mc. SSB and even CW performance is very poor, if not impossible. The SLRM may as well not have a BFO since it doesn't function adequately. The BFO tube is only running +10vdc on the plate (the 220K ohm plate load resistor significantly drops the B+) and then the BFO circuit is electrostatically-coupled to the detector which results in a totally useless BFO. It's likely that because of the SLRM's all-aluminum construction there was more RF leakage than the <400pW specification. Scott obviously intentionally reduced the BFO output until the RF leakage was <400pW probably figuring that the SLRM was going to be for shipboard entertainment where the barely-functional BFO shouldn't pose any problems. Nowadays, it's very easy to replace the 220K BFO plate load resistor with a resistor value around 5K which will increase the plate voltage on the BFO tube to around +85vdc. This increases the rms voltage of the BFO output to the point where SSB and CW demodulation is possible. The RF Gain will still have to be reduced to the point where the signal to BFO injection ratio provides good demodulation.

IMPORTANT NOTE:  Another significant problem is the SLRM's AC-DC power input which MUST NOT be operated with the original 3-wire "twist lock" plug and a modern grounded (3-wire) AC power plug connected directly to the house AC line. To do so will connect the line return power wiring directly to chassis which prevents the dial lamp from lighting and takes some of the bias voltages to chassis. Modern house AC wiring has neutral connected to ground (at the breaker box) and this will conflict with the receiver power input wiring that assumed the two AC lines would be "floating." To safely operate the SLRM (or any AC-DC receiver) requires the use a 1:1 isolation transformer. This provides the "floating" two-wire AC plus separate chassis ground that the SLRM design anticipated. The isolation transformer should use a three-wire cable/plug on the input side. The input side ground pin should be wired directly to the transformer's output socket ground pin only. The AC output of the isolation transformer winding will be "floating" which allows the use of the original three-wire power cable and twist-lock plug that grounds the chassis but not either of the "floating" AC lines. The original power cable on the SLRM used a three-wire "twist-lock" (actually, two wires and a shield-ground) which can still be used if powered with an isolation transformer set-up as described. Be sure to have an "ON-OFF" switch on the AC input to the isolation transformer. This can also be operating the isolation transformer from a switchable three-wire power strip. If the isolation transformer is left connected to AC and to the SLRM, then the two line bypass capacitors will be passing a small amount of current to chassis ground - even if the SLRM is turned off (check the schematic.)

 

TecRad LRR-5 from 1945

Technical Radio Company (TecRad)  - LRR-5

Technical Radio Company was founded in San Francisco, California in 1937 by Clayton Bane and George Weiss. Bane was an assistant to Frank Jones at Western Wireless, Ltd. (1932 to 1934) where he helped install the first two-way radio system at Alcatraz Federal Prison. Many of Bane's crew at Western Wireless went onto work at Eitel-McCollough (Eimac) but Bane went on to form his own company called Technical Radio Company. TecRad (as it was sometimes called) became a prime contractor for the U.S. Navy building high quality shipboard entertainment receivers and a couple types of small transmitters. Only a few companies built Navy acceptable shipboard entertainment radios since there was a strict requirement that no more than 400 pico-watts of LO leakage was allowed on the antenna. TecRad claimed that only 100 pW was present on the antenna with their receivers. Scott Radio Laboratories built the SLR and RBO receivers that are the most common of the "low radiation" WWII shipboard entertainment receivers but TecRad also produced their versions during the war designated as "LRR" with numeral suffixes from 1 up to 6 (LRR = Low Radiation Receiver.) The TecRad receiver shown is the Model LRR-5 from May 1945.

The LRR-5 is typical of the WWII shipboard entertainment receivers in that robust, high fidelity audio is delivered to selectable multiple output impedances (six impedances from 16 ohms to 800 ohms) since many ships had various kinds of audio loads depending on the size and layout of the audio distribution within the ship. A front panel speaker switch is provided to allow disconnecting specific speaker lines depending on how the ship's speaker system was wired. Most systems probably had the speaker switch wired to allow the local radio room speaker to be disconnected while the ship's audio system remained on. 15 tubes are employed in the LRR-5 including an 0C3 voltage regulator and push-pull 6V6 audio output tubes. Also, a 6E5 cathode ray tuning indicator tube is provided. The frequency coverage is typical of shipboard entertainment receivers with the AM-BC tuned with Band 1, Band 2 tuned from 2.0mc to 6.5mc and Band 3 tuned from 6.5mc up to 18mc. Also, a very accurate logging scale is provided. Single preselection is used along with two IF amplifiers with three selectivity bandwidths available. A phonograph input is also provided. Like some of the Scott Radio Labs' SLR/RBO receivers, a BFO is included - just in case the receiver might be needed for CW reception and a Send-Receive switch is provided - just in case the receiver had to be used for two-way communications. Unlike the Scott receivers, the LRR-5 includes separate RF and Audio Gain controls thus when the BFO is tuned on, the RF Gain must be reduced and the Audio Gain increased for proper CW reception. 

Performance of the LRR-5 is impressive. The audio is high quality and with push-pull 6V6 tubes in the output there seems to be quite a bit of power available. Bass response is very good and Shortwave Broadcast stations that are playing music sound incredible. AM-BC sounds very good with plenty of sensitivity available - after all, you might be trying to "pull in" an American AM-BC station while in the middle of the Pacific Ocean. Although only a single RF stage is provided, images are not apparent in normal reception above 15mc as would be expected. Alignment of the front end provides L and C adjustments for all three bands and the IF transformers are permeability tuned. Strategic shielding is used to keep the LO leakage down so there are a few shielded boxes in the receiver's front end. High quality Peerless transformers (Altec-Lansing) are used in the LRR-5. One has to also note the perhaps intentional resemblance that the LRR-5 has to receivers built by Mackay Radio and Telegraph Company around the same period. The LRR dial material is exactly the same opaque white plastic (side illuminated) that will glow purple with intense rear lighting and the gray panel with white nomenclature is quite similar to that period Mackay receivers. Perhaps it was intentional so that the LRR-5 would fit in with Mackay Radio equipment that was in use on many ships.

In 1948, Clayton Bane stated that due to some personal reasons and due to the fact that his building lease was not going to be renewed he was closing down TecRad. According to Bane the company was profitable but there was also some difficultly in that the Navy wanted TecRad to remain exclusively a Navy Contractor and not be able to produce for the civilian market. Bane went on to form a successful advertising business. Bane died in 2003.

 

Minerva Corporation of America - W117 "Tropic Master"

The Minerva Tropic Master is an eight-tube receiver that covers AM-BC and provides one Shortwave band, 5.5mc to 18mc (there are some minor variations in the shortwave coverage with different production runs.) The cabinet is metal and features a fold-down front cover along with a carrying handle. The Tropic Master is an AC-DC powered receiver. There were two circuits used with the earlier version having push-pull 50L6 tubes and a series-parallel filament string. This version could also be modified to use two 25L6 tubes by changing the filaments to series making the entire string a series load. NOTE: The schematics in Riders VOL. XV have several errors including the 50L6 filament connection. The later circuit uses two 50A5 tubes and a 35Z5 rectifier. The P-P audio seems a bit much for the small built-in PM speaker. Four controls provide Volume and ON-OFF, Tone, Band Select and Tuning. The rear panel of the cabinet has a door to allow access to the power cord and the antenna terminals. The Tropic Master didn't have enough shielding to be used onboard ships as the LO leakage would have exceeded the minimum acceptable level of 400pW on whatever antenna was used with the receiver.


photo above: The Tropic Master with the front closed

Minerva advertised that they had supplied the Tropic Master to the military (both Navy and Army) as a "Morale Radio" - that is, a radio primarily for entertainment in barracks or other shore locations. Apparently, a few Tropic Masters did serve in that capacity as there seems to be enough first-hand accounts to believe Minerva's advertising was essentially true. Certainly though, the majority of Tropic Masters were sold post-WWII. The selling price was $75 and many were sold out of the PXs at various military bases during late-1945 and through 1946. The Minerva W117 schematic in Riders' VOL. XV is dated June 1945 and this data shows the two different versions that are documented. There are apparently other minor variations that were incorporated into the receiver circuits but these were not documented.

The Tropic Master receivers have quite a following and there is ample information available on the Internet. The Tropic Master (T-M) shown is the second one I've owned. This currently-owned T-M was found at a Hot August Nights' Swap Meet (a car swap meet in Reno) about 12 years ago. I saw it there one year and passed it up because of the asking price was $80. Next year, to my surprise, there was the same seller with the same T-M - this time for $50. I purchased it since I had always regretted the fate of my first T-M. My first T-M was given to me for shortwave listening when I was fifteen years old by Phil Rios of Rios Radio-TV Shop, my old mentor in radio repair (where I had worked summers as a teenager.) I never did get it to work because, like many of these receivers, the 25Z6 rectifier was missing and, in the mid-sixties, the 25Z6 was difficult to find (read - expensive, for a teenager.) Eventually, I used the cabinet for a power supply and lost the chassis in one of several moves. Luckily, my currently-owned T-M is in excellent original condition and does function (filter cap replacement was necessary though.) This receiver is the earlier version with the P-P 50L6 tubes with parallel filament connections.

 

The Crosley Corporation  -  REO

Crosley seemed to have most of the WWII contracts for the smaller "Morale Radios" destined for shore use. Though the Scott SLRs and RBOs along with the TecRad LRRs could and were used aboard ships, the smaller radios were generally designed to be less expensive and this usually resulted in excessive LO radiation which prohibited their use aboard ship. Though some of the more elaborate "Morale Radios" for shore use were sometimes found in metal cabinets (like the Tropic Master above,) the REO is housed in a wooden cabinet that is painted Navy gray. This simple radio covers AM BC only. The controls are left to right, Volume, On/Off and Tuning. The Navy wanted to be sure that every user was aware that the REO was strictly "land use only" and provided a large red warning tag stating so ("Unsafe Radiation Limits" refers to the radio's Local Oscillator signal radiation from the antenna and elsewhere in the circuit since the cabinet provides no shielding.) 

WWII U. S. Navy Contractor Designators

During WWII most U.S. Navy equipment built for the war effort was manufactured or assembled by contactors. Many times the items built would be a specific product model of a particular company and would have exactly the same company parts and same assembly techniques but the item was assembled by a contactor company. The contactor-built equipment had to meet the same specifications and therefore most of the time the equipment performs exactly the same as another example built by the original manufacturer or another contactor. Each contactor or component supplier had a specific letter identification that was incorporated into the specific model number. So, if a piece of Navy radio equipment is ID'd as CFT-43600, then that piece of equipment was built by Federal Telephone & Radio Corporation. To the right is a list of designators used for some of the popular contactor and component supplier companies during WWII. CAN  -  Sangamo Electric

CAW  -  Aerovox

CAY   -  Westinghouse

CBN  -  Central Radio Labs

CCT   -  Stromberg-Carlson

CD     -  Cornell-Dubilier

CFN  -  Farnsworth Televison & Radio Corp.

CFT   -  Federal Telephone & Radio Corp.

CG     -  General Electric

CHH  -  Arrow-Hart Hagerman

CHL  -   The Hallicrafters Co.

CHS  -   Sylvania (vacuum tubes)

CJC  -  Howard B. Jones

CKP  -   Air King Products Co., Inc.

CKR  -   KEN-RAD  (vacuum tubes)

CLF   -   Littlefuse Labs

CMA  -  P.R. Mallory & Co.

CMC  -  Clarostat Mfg. Co.

CME  -  Radio Manufacturing Engineers, Inc.

CN   -   NEMS (National Engineering Machine Shops)

CNA  -   National Company Inc. 

CND  -   Andrea Radio Corp.

COL  -   Collins Radio Co.
CPN  -   Panoramic Corp.

CRA  -  Utah Radio Products Co.

CRC  -   RCA  (Vacuum Tube Division)

CRV  -   RCA-Victor or RCA Mfg. Co.

CSF   -   Sprague Specialties Co.

CTD  -   Tobe Deutschmann Corp.

CWQ  -  Wells-Gardner Co.

CWS  -   Stewart-Warner

CYM -   Yaxley-Mallory

CZC  -   Scott Radio Laboratories, Inc.

CZR  -   Zenith Radio Corp.
 

 

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

 

 

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

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 "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-right 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. In either case, you'll have to reduce the RF Gain and AF Gain or switch off the loud speaker.

 

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. It's likely that it was at least 1944 before any AR-8510s were in use. The AR-8510 shown in the photo above is dated NOV 1944 and has a serial number of 2774 making it an early version of the receiver. It was more than likely 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. 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 (160M operation was problematic at the time.)

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 above in 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.

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.

 

Aircraft Radio Equipment - USAAF

BC-224-H - 1942

RCA Manufacturing Company, Inc.  -  BC-224 Series and BC-348 Series  -  Various Other Contractor Companies

RCA introduced the BC-224 Aircraft Receiver in 1935. It ran on the then popular 12 volt power systems used in most aircraft. The initial version of the BC-224 had the tuning dial on the left side of the front panel. This version is usually designated as the BC-224-A and the number produced was very small which was typical for pre-WWII military contracts. As aircraft power systems improved 24 volts became the standard voltage and that required a change in the radio equipment to be installed in the newer airplanes. RCA redesigned the BC-224 to operate on 24 volts and this receiver was designated as the BC-348. The BC-224 continued to be built for installation into earlier aircraft while the BC-348 was produced for modern aircraft installations. Both receivers were built by RCA Manufacturing Co., Inc., a division of RCA that built all of the commercial and military radio equipment for RCA (before WWII.) When WWII began several other radio companies became contractors for BC-348 construction,... Belmont Radio, Wells-Gardner Co., Stromberg-Carlson, to name a few. Only one contract for BC-224 receivers was built by another company other than RCA Manufacturing Co., Inc. and the last contract for the BC-224 appears in 1942. The BC-348 was produced through WWII and total quantity produced is certainly well over 100,000 receivers (over 50,000 receivers alone were produced by Wells-Gardner Company.)

The BC-348 operates on 24-28vdc with the high voltage (~+220vdc) provided by an internal dynamotor. Many thousands were built during WWII by many different contractors building many different versions within that time period. The circuit used eight tubes with the heaters originally wired in dual-series for 24vdc operation (each of four 6 volt tube heaters in series would operate on 24vdc.) The early circuit provided two RF amplifiers, a Mixer, a Local Oscillator, an IF amplifier stage, a combination 2nd IF amp and BFO, a combination 3rd IF amp and Detector/AVC followed by a type 41 audio output stage (this was changed to a 6K6 in some versions.) These versions will have a 991 neon lamp acting as a regulator on the local oscillator and an antenna trim control. Construction makes use of four component boards resulting in extensive use of wiring harnesses. The Crystal Filter and BFO are in fully shielded cans. This early version is usually referred to as the "Grid Cap" version since these types of tubes are used. This early version was difficult to work on and was expensive to build. To reduce costs, the Q, N and J versions were introduced. These versions eliminated most of the component boards and used "point to point" wiring to reduce costs and ease rework. This version is called the "Single-ended Tubes" version since "non-grid cap" tubes are used. The later circuit used two RF amplifiers, a converter stage, three IF amplifiers, a duplex diode/triode provided Detector, AVC and BFO functions and a 6K6 provided the audio output. The later versions eliminated the shielded Crystal Filter, Antenna Trim control and the fully shielded BFO. The audio output impedance was internally selectable at "low Z" which was around 300 Z ohms or "high Z" which was around 4000 Z ohms (on later versions.) Some BC-348s will have a decal on the front panel indicating if the "low Z" was optioned. A selectable crystal filter was also included in the circuit. The dual dial lamps were adjustable for brightness and were wired in series through a potentiometer and fixed resistor. Frequency coverage was from 200-500kc (not on the B or C versions) and 1.5-18mc. The military considered the two versions of the BC-348 to be interchangeable with virtually no difference in performance and operation.

When the receiver was installed on its FT-154 shock mount and installed in the aircraft, an eight pin Jones plug mated with a receptacle and cable that exited from the rear of the mount containing the 28vdc input, the remote stand-by relay function and an audio output line. The BC-348 was generally interconnected with the transmitter to control boxes allowing the transmitter's control relay to provide antenna switching, receiver stand-by and providing side tone monitoring which allowed for full "break-in" keying. Since there are so many variations, military collectors have generally divided the BC-348 into two groups, early types (B, H, K, L, O, P & R) with grid cap type tubes ("Grid Capped Tubes" version) and the later versions (J, N & Q) with single-ended tubes ("Single-Ended Tubes" version.) Several of the earlier versions were rebuilt into later configurations, especially to add the 200-500kc band. Many different contractors built BC-348s but Wells-Gardner Co. probably built the greatest quantity of receivers and is the most commonly seen manufacturer.

The BC-348 became available as surplus almost immediately following WWII and was easily available for several decades from many surplus dealers. Many were available in the original box in the late-forties. This allowed hams the ability to purchase a great performing receiver at a reasonable price - NOS and still in the crate for about $100. Many surplus dealer offered "AC power supply conversions" for as little as $15, so the buyer didn't have to do the work. The down side is that today it is almost impossible to find a BC-348 that hasn't been modified. Typically, the dynamotor was removed (and discarded) and an AC power supply added. This mod was fairly simple and usually didn't compromise the receiver's performance (other than adding some hum to the audio output if the power supply wasn't well-filtered - which most weren't.) Unfortunately, most of the dealer power supply mods used a separate AC power toggle switch that resulted in a non-original hole above the CW OSC. switch.  


photo above: RCA Manufacturing Co. BC-348-C  - earlier "Grid Cap Tubes" version - ca: 1941

Many other dubious mods were published in various surplus conversion books from the fifties and sixties that did compromise the BC-348's performance. Adding an S-meter or adding an audio output section was common. Additionally, many hams would sometimes drill the case with lots of .25" holes thinking the receiver needed extra cooling because of the added AC power supply rectifier tube. However, it's still possible to find unmolested examples and many receivers just have the AC power supply added. These examples usually aren't difficult to restore to original condition. Both versions the Grid Cap version and the Single-ended Tube versions are great performing receivers if restored to original or when conservatively modified (AC PS only.) Accurate alignment is also necessary for top performance.

If you're interested in restoring your BC-348 or BC-224 receiver back to its original configuration with the installation of the correct DM-28 or DM-24 dynamotor, go to our web article "Rebuilding the BC-348 Family of Receivers" This article tells you about all of the "pitfalls" that might await you in this seemingly easy project. Also includes information on other aspects of the restoration of these fine performing receivers.

photo left: Wells-Gardner BC-348-Q 1943. This contract produced over 40,000 receivers alone. Note that these "Single Ended Tubes" versions eliminated the "ANT. ALIGN." (antenna trimmer) control that was located above the Antenna and Ground input terminals. Many other cost reductions will be found inside the Q, N and J versions. However, the great  performance is retained and these receivers are very easy to do any rework to.

 

General Electric - BC-375-E

Though the BC-375 was designed in the early thirties and utilized parts and technology from a decade earlier, it found a long-term usage with the Signal Corps due to its ease of operation and reliability.  Its earlier kin, the BC-191, was the first version built from the mid-thirties on up to mid-WWII. Around the beginning of WWII, an airborne version was necessary and the BC-375 became the designation for a slightly different transmitter for use in larger aircraft. GE got a manufacturing contract for several tens-of-thousands of BC-375 that were built through the first half of WWII. Commonly used on B-17s, the SCR-287 set-up was found on thousands of those bombers. Hopelessly outdated for aircraft use, towards the middle of WWII the ARC series of transmitters-receivers were introduced, along with the Collins ART-13A, to replace the BC-375. At the end of the war, thousands of BC-375-E transmitters remained unopened in their original crates.

The BC-375 uses four VT-4-C triode tubes (type 211) and a single VT-25 (10Y) triode with one VT-4 used as the Master Oscillator, another VT-4 as the Power Amplifier and two VT-4 tubes for the P/P Modulator. The VT-25 serves as the speech amplifier in the Voice mode (AM,) as a 1000hz oscillator in the Tone mode (MCW) and as a sidetone oscillator in the CW mode. Power is provided by the aircraft battery/charger system (24 to 28vdc) and by a high voltage (+1000vdc) dynamotor (PE-73.)

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The transmitter frequency range is determined by which of the seven Tuning Units is installed in the transmitter. The coils and condensers and connections for the MO and PA are contained in each TU. The range of frequencies is from 200kc to 500kc and from 1500kc up to 12500kc using the various TUs. The controls aligned vertically on the right side of the transmitter make up the wide range antenna coupler for the transmitter. The BC-306-A located to the right of the BC-375 is the LF Antenna Tuner allowing further extension of antenna matching ability below 800kc using the typical trailing wire antenna. Power output is between 50 and 90 watts.

The BC-375 provides full break-in keying by allowing the elaborate internal antenna relay to control the receiver antenna and the receiver standby circuit. Additionally, external inputs via the PL-64 cable allow remote microphone and key operation along with remote power control. The aircraft was usually set-up to allow the pilot to also access the transmitter/receiver for various reasons.

After WWII, the BC-375 was available surplus for about $15. The various TUs were also available at "give-away" prices. This lead to many hams buying  the BC-375 for an economical way to get "on the air." Unfortunately, most hams tried to run the transmitter at full power "as-is" or tried to rebuild it into something that it was NEVER intended to be - a ham transmitter. The end result was a bad reputation that the BC-375 was unstable, sounded awful, created horrible TVI and was only useful as a resource for parts to build other ham projects. Though TVI was a major issue in the fifties, today's strong TV cable and satellite dish signals are usually not affected by the BC-375 operation. The transmitter can sound fairly good if it is carefully operated after a thorough check out that includes a precise adjustment of the neutralization and reducing output power to about 50 watts.

For the ultimate information source on how to successfully operate the BC-375 "on the air" without enduring endless criticism of your signal's lack of audio quality, go to our web-article "Successfully Operating the BC-375 on the Ham Bands Today" - navigation link in the Index below.

SCR-287  -   At the WHRM 2009 to 2012

The SCR-287 comprised a complete liaison radio station installed onboard various bombers and transports during WWII. The transmitter used was the BC-375 along with the BC-348 as a receiver. The other components shown are the BC-348-Q receiver which does run on its original dynamotor from the battery supply, the Lionel J-47 telegraph key and the Shure Bros. carbon microphone, the T-17. The speaker is an LS-3, although these were never used in the SCR-287 or onboard the aircraft. Four BC-375 Tuning Units are mounted in their CS-48 containers on the wall. The olive-drab console is not a WWII vintage item - it's homebrew. It features a fold-down desk, a sound-proof (almost) compartment for the PE-73 dynamotor and a bottom shelf for the four storage batteries (four 12v batteries in series-parallel = 24vdc.) The panel to the left of the BC-348 has all of the remote connections for receiver audio output, receiver stand-by, xmtr CW sidetone select, xmtr microphone input and xmtr key input. The photo shows the station as it was set-up in the Western Historic Radio Museum in Virginia City, Nevada around 2009. The station is now set up in Dayton, Nevada where it runs on a PP-1104 high current +28vdc power source (instead of +24vdc worth the batteries.)

 

Setchell Carlson, Inc.  -  Model 524 Beacon Receiver

U.S. Army Signal Corps Designation:  BC-1206-CM
 

The Model 524 Beacon Receiver is a small size, light weight aircraft receiver that covers 195kc up to 420kc. The circuit is a five tube superheterodyne utilizing loctal type tubes. The receiver is entirely powered by the +28vdc aircraft battery-charger buss. No higher voltages are required to operate the 524. The "PHONES" output is 300 ohms Z although internally the output Z can be switched to 4000 ohms Z, if desired. The IF is 135kc. The tubes used are RF Amp 14H7, Mixer 14J7, IF Amp 14H7, Det-1st AF 14R7 and AF Output 28D7.

The 524 had a rather interesting use during WWII. These small receivers were installed into the instrument panels of airplanes that were going to flown to specific destinations by WASPs (Women's Airforce Service Pilots.) This would generally be smaller fighter types of aircraft but did include larger aircraft as well. The airplanes were ferried from the manufacturer to either an airport or an export facility. Since the destination was known, the 524 provided a way to navigate to a specific airport via the beacon "beam." At that time, airport beacon transmitters also provided weather reports and other information necessary for piloting aircraft. Once the airplane was delivered, the 524 was usually removed from the instrument panel and returned to the aircraft factory where it was eventually recycled into another aircraft destined for delivery.

The 524 is very sensitive with a specification of 3uv for 10mw output. The receiver shown in the photo to the left does function quite well and receives many NDBs and other signals in the 195kc to 420kc range. It is very small weighing only about 4 lbs and measuring 4" x 4" x 6.625". The four holes in the front panel surrounding the dial plate are tapped and are provided to allow mounting the 524 into a standard instrument panel opening (3.125".) 

 

r-44.jpg (22294 bytes)

the Hallicrafters, Inc. - R-44/ARR-5

This VHF receiver provided airborne search capabilities and was designed to find enemy radar or other signals. The R-44 is a 14 tube superhet tuning from 27.8 to 143 Mc in three bands and receiving AM, CW or FM signals. Motor-drive tuning provided a "search" scanning mode. Outputs for visual indicators were also provided. A special "stub" antenna was used (AT-38) and a separate power pack (PP-32) provided the power for the receiver (and added three more tubes, although these were to provide B+ for three individual receivers.) Sometimes this receiver is called the "Airborne S-36" based on its similarity to Hallicrafters' VHF base receiver, the S-36.

 

the Hallicrafters, Inc. -  R-45/ARR-7

Like the receiver above, the R-45 was an airborne search and surveillance MF and HF (.55 to 43mc) receiver that was primarily used for visual analysis of enemy radar and other types of signals. The Panadaptor and Video Outputs were designed to feed into specific airborne versions of typical panoramic adapters and to oscilloscopes. The oscilloscopes sometimes had built-in oscillators to create lissajous patterns for audio analysis of incoming signals (Video output is from the 6V6 audio stage of the receiver.) The panoramic adapters monitored the output of the Mixer stage of the receiver and provided a visual representation of the spectrum surrounding the receiver's IF passband. This allowed the operator to "see" signals that were outside the receiver's passband and couldn't be heard - but they could be seen on the panadapter, allowing the operator to tune to the signal for investigation. The R-45's circuit is very similar to the SX-28A, although "stripped down" to the essentials and considerably lightened for aircraft use. 12 tubes are used (not including the rectifier that is located in the PP-32 power pack.) Some of the similarities to the SX-28A are the use of the same Micro-set coils in the front end, six selectivity steps with three utilizing the crystal filter. The differences from the SX-28A are the use of a "re-radiation" tube ahead of the RF amps, a Noise Limiter which is just a clipper circuit, use of a VR tube, no bandspread and the "militarily basic" audio output system which is just a capacitive coupling from the 6V6 plate to drive the headphones. Up to three combinations of the R-44 or the R-45 receivers could be powered by the PP-32 power pack that provided the heater voltage (6.3vac) and the B+ (+275vdc) but the scanning motor drive was powered by the aircraft battery system (+24vdc.) Additionally, the PP-32 operated off of 115vac 400 cycle provided by the aircraft's ac system.

WWII Allied Radio Equipment

Kingsley Radio Company, Melbourne, Australia - AR7

During WWII, both the Allies and the Axis copied the famous National HRO Receiver. The Axis copies were shown in a 50th Anniversary brochure that National published in 1964. Probably the "knock-off" that got the most use was the Kingsley AR7, built during WWII by Kingsley Radio Company of Melbourne, Australia. Kingsley submitted the design (probably around 1940) as the K/CR/11 but after the design was accepted, the receiver became the AR7. Though the AR7 uses a micrometer dial and plug-in coil sets, that about as far as copying the National HRO went. The AR7 did use two RF amplifiers but uses a Converter stage instead of a separate LO and Mixer. Eight "American-type" tubes are used in the receiver and two in the power supply. Frequency coverage is 138kc up to 25mc using five plug-in coil sets. Two IF amplifiers are also used operating at 455kc. An S-meter amplifier circuit provides the user with a front panel Calibration control. The audio output is a single 6V6 to a dual impedance output transformer that provides 600 Z and 1750 Z impedances. A Crystal Filter is provided. All AR7s are rack mounted and came with a rack mounted power supply that operated on either 240vac or 12vdc. A rack mounted speaker was also included. Some receiver housings had four coil storage cubbies, two on each side of the receiver. Normally, the receiver was lowest in the table rack with the speaker in the middle and the power supply on top. The Australian Army referred to the AR7 as "Reception Set No.1" and sometimes had the panels painted green. Normally, the AR7 panel, since it was a stainless steel overlay, was left unpainted with the nomenclature slightly polished to improve readability.

After WWII, many AR7s were installed at various airports around Australia where they served as tower and air to ground receivers. Many were modified to have crystal controlled frequency reception with the LO coils removed from the coil set and a crystal controlled fixed frequency oscillator installed to allow specific frequency reception with no tuning. Some receivers also had the AVC modified while others had different scales installed on the S-meter. Most AR7s don't have the original audio output transformer as it seems this component was easily damaged. Banks of AR-7s could be found at various airport communications facilities and some tower installations would feature a fairly stock AR7 that could still be tuned. Today, many AR7 receivers are in dismal condition due to heavy use followed by indifferent storage. Most receivers are incomplete and don't have the original power supply or speaker panel. Many suffer from corrosion and are non-functional.

Performance of a functional AR7 is impressive. They are similar to HROs but do have their quirks. For instance, the micrometer dial tunes "backwards" when compared to the PW-D of the HRO. That is 500 on the AR-7 is the lowest frequency of the coil set installed while it's the highest frequency with an HRO. Also, the S-meter works "backwards" with FS being "0" and mechanical zero being "S-9." The ability to calibrate the S-meter for the particular coil set being used is a nice feature and not one that is found on the HRO. Coil sets are steel construction and very heavy while the HRO sets are all aluminum. With all of the use that the AR7 provided, both in WWII (and especially post-WWII) it obviously was a great performer and very stable. The AR7 shown above is functional and doesn't have too many modifications to it. Great audio, although it doesn't have the original audio output transformer but rather has the commonly installed replacement transformer made by Rola. Unfortunately, the Rola transformer only has a single 600 Z ohm winding for the audio output.

 

Canadian Marconi Company  -  CSR-5

The Canadian Marconi Company was contracted to build a high quality receiver for the Royal Canadian Navy in early 1943. Most CSR-5 receivers were built in 1944 and were part of the first delivery of  receivers to the RCN. Sometime in 1944, the CSR-5A was introduced. The CSR-5 was used for several purposes, even though its primary intended use was aboard ship. Shipboard use required extensive shielding in the receiver to allow its operation along side other equipment without causing interference or radiating the LO from the antenna. Apparently, the RCN found other uses for the CSR-5 and most were not installed onboard ships until the early 1950s. The receiver's frequency coverage was in two sections, 75kc to 530kc and 1.5mc to 30mc, in six bands. Each scale on the large illuminated dial was color coded. The CSR-5A replaced some of the 6SK7 tubes with 6SG7 tubes (in the RF and IF) as the major change, however there were many other minor changes in the cabinet style, power connector orientation, dial scales, etc. Many of the earlier CSR-5 receivers were retrofitted with the 6SG7 tubes which may cause confusion as to the receiver's original designation. Additionally, the silk-screen was not changed for the chassis, so many CSR-5A receivers will have modified 6SK7 to 6SG7 tube identification.

The CSR-5 has eleven tubes in the receiver with two RF amplifiers, Mixer (also provides Xtal Osc function,) LO, two IF amplifiers, NL, Det/1AF, AF output and Voltage Regulator. The RF Gain control is a stepped attenuator type with about 10db of change for each step. AF output is 2 watts into a 10K Z load for loudspeaker, 500 ohms Z line audio and both Hi-Z and Lo-Z 'phones. A separate power supply is required and the VP-3 provided 12vac Filament (series/parallel connections for all 6.3vac tubes except the BFO and LO that use series resistive loads) and +250vdc B+ with an input requirement of either 12vdc (vibrator PS) or 115/230vac. An AC only power supply was also available and designated as the WE-11. Two 6X5 rectifiers are used in the VP-3 bringing the receiver's total tube count to 13 tubes. The later version CSR-5A was mostly built after the initial contract of CSR-5 receivers although it could be possible that the production overlapped. CSR-5A receivers were built up into 1945. The receivers were used actively through most of the 1950s.

The CSR-5 and 5A are found in a variety of different paint colors with the most common color found being a smooth finish, light cream color with a slight greenish tint. Smooth gray is also found when the receiver was part of a rack system. Gray wrinkle finish is common in the stand-alone receivers. Different shades of gray are often encountered along with black wrinkle finish. Many different shade and texture variations will be found along with both black or white nomenclature. Some paint combinations are original but most of the unusual variations are from military repaint jobs. The CSR-5 shown in the photo above has the name plate mounted on the front panel. This is not standard as most receivers have the name plate mounted on the top lid of the cabinet. Only the CSR-5A will have the "Marconi" script along with "CANADA  CSR-5A" silk-screened on the center area of the escutcheon. The CSR-5 is a good performer with all of the characteristics (both good and bad) found in mid-forties military receivers. Due to the VR tube and filament loads on the LO and BFO tubes, the CSR-5 exhibits very little drift after a short warm-up. Sensitivity is competitive with mid-1940s designs and although a crystal filter is included it doesn't have a front panel phasing control. 

 

WWII COMM GEAR PART 1                                              Return to Home Index

 

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