Western Historic

RADIO  MUSEUM

 ~ WWII Communications Equipment ~ 

(U.S. Navy  &  U.S. Army Signal Corps)

 ~ Military-Commercial Communications Equipment  - 1932 to 1959 ~

~ Post-War Ham Gear  - 1946 to 1959 ~
 

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I1LOV, Augusto Lovisolo, Varese, Italy  (ca:1958) with Collins KWS-1 and 75A-4  (photo from his QSL card.)

Radiomarine Corporation of American (RCA)  -  RAZ-1 (AR-8503, AR-8503-P, RM-6)

 RAZ-1 was the Navy designation for a group of equipment consisting of a four tube longwave TRF receiver with regenerative detector, a matching one tube preselector and a one tube AC power supply - all built for shipboard use. The Navy number for the receiver is CRM-46092 but it was also known as the AR-8503 in commercial applications. The AR-8503 was in use as early as 1938, mainly in commercial shipboard radio rooms. The receiver circuit uses one RF amplifier, a regenerative detector and two stages of AF amplification. The one tube preselector is Navy number CRM-50092 or commercial number AR-8503-P and the AC power supply is Navy number CRM-20096 or commercial number RM-6. Tuning is from 15 KC to 600 KC in four bands. The Preselector was used to reduce regenerative signal radiation to the antenna in addition to increasing sensitivity and selectivity. The National Type "N" dials are 0-100 scaled with 180 deg. rotation and a calibration chart is included in the manual . The RAZ-1 could be operated from batteries if necessary. The receiver and preselector panels are beautiful machine-textured aluminum with a matte-chromium finish. The receiver case is copper-plated steel under the gray wrinkle finish and uses "shock-mount" feet that were screwed to the operating table, (the pre-selector and power supply were normally screwed directly to the operating table.) The Navy contract is dated December 2, 1941 - just five days before the attack on Pearl Harbor. The RAZ-1 equipment shown are all assigned identical serial numbers - SN:65. Performance of this operational RAZ-1 is incredible with an ability to extract weak signals out of the noise that is impressive. NBDs from all around North America, LW BC stations and Navy VLF RTTY stations from around the world are easily received. Output is to a set of Western Electric 509W earphones as recommended in the manual. (See our "Vintage Longwave Receivers" webpage for an in depth article about this receiver.) 

Radio Corporation of America - DZ-2

RCA built this radio direction finding receiver for the Navy for use in search and navigation. The DZ-2 dates from 1939 though there were additional contracts during WWII. Using 8 tubes in a superhet circuit and tuning from 15 to 70 kc and from 100 to 1750 kc, the DZ-2 used a rotatable dual loop antenna and a fixed vertical antenna (usually a "T" wire from the cockpit to the tail) to determine "true" direction (called Uni-lateral Reception/Sense.) Non-directional and Bi-directional options were also provided. The dual loop antenna was mounted in an aerodynamic housing on the exterior of the fuselage and the remote drive control provided a readout of the loop's relative position for the radio operator. The DZ-2 also featured a BFO and Audio Filters. The receiver uses a cushioned shock mount. Power provided by battery and external dynamotor.

Andrea Radio Corporation (for RCA)  -  RAK-7 (CND-46155) and RAL-7 (CND-46156)

Designed for the Navy by RCA in 1935, the RAK and RAL receivers were used in various shipboard applications (also submarine) up through WWII. The two receivers were ruggedly built and reliable in their design simplicity. The RAK is a six tube TRF receiver with regenerative detector that covers 15 kc up to 600 kc in six tuning ranges. The RAL is also a six tube TRF  receiver with regenerative detector but covers 300 kc up to 23 mc in nine tuning ranges. Tube line up is the same for both sets with four 6D6 tubes and two type 41 tubes. Both receivers use a dual dial readout (0/00 to 10/00) that must be correlated to a graph in the manual for tuned frequency. Each receiver has its own separate power supply, the CRV[CND]-20131, which provides power through a ten foot long cable that connects to a terminal strip inside the receiver. The power supply uses a 5Z3 rectifier, an 874 regulator tube and an optional 876 ballast tube that was supposed to be used when the AC line voltage was subject to fluctuations (supposedly that would cause instability in the RAL receiver at higher frequencies.) Meters on each receiver monitor the tube heater voltage (right) and the audio output (left.) The RAK receivers were intended for CW or MCW reception only as a low pass filter is permanently connected in the circuit to limit the upper audio response to about 1200 hz. The RAL has the option of allowing the low pass filter to be switched out of the circuit (switch in "BROAD" position) and can therefore can be used to receive voice transmissions along with CW and MCW signals. An elaborate audio AVC system is employed in both receivers to limit overloading and also to allow operation in heavy static conditions. An audio bandpass filter system is also employed in each receiver that allows the operator to select various audio frequency ranges via a front panel switch. The audio output Z is 600 ohms and is intended to drive earphones (but it will drive a 600 ohm Z speaker quite well.) The RAL and the RAK receivers were designed to work together through a separate control box (CRV[CND]-23073) that allowed the operator to monitor two frequencies simultaneously (each receiver tuned to different frequencies with the audio from each combined) and also to control power to each receiver.

The RAK and RAL receivers are surprisingly good performers and interesting to operate. The RAK is a first class longwave receiver and can easily pick up NDBs from all over North America, WWVB or JJY (Japan's LF WWVB equivalent at 40KC) , along with LW BC stations and any of the VLF Navy RTTY stations worldwide. The RAL is also an excellent TRF receiver that will function quite well on the HF ham bands, even copying SSB stations with minimal drift (since there is no LO or BFO to worry about.) SW BC and AM BC can also be received with audio quality that is somewhat restricted but acceptable. The RAK-7 and RAL-7 pair shown in the photo are from 1945 and, like most RAK/RAL receivers, they were manufactured by Andrea Radio Corporation. Use of [ND] in Navy designation indicates Andrea manufacture and [RV] indicates RCA-Victor. (See our "Vintage Longwave Receivers" webpage for an in depth article about these receivers.)

CFT-46300, RBA-6 from 1945

Federal Telephone & Radio Corporation (for RCA) - RBA Series

In the late thirties, it was becoming apparent that a replacement receiver was necessary for the aging RAK series of longwave receivers. The new design was going to blend the advantages of the TRF designs of the RAK but eliminate the regenerative detector in an effort to keep the radiation on the antenna to a low level that prevented enemy DF of the receiver location. Additionally, the low-level of radiation allowed the receiver to operate in the presence of other receiving and transmitting equipment and radar without interference. In order to allow demodulation of CW signals a "tracking" beat frequency oscillator (BFO) was incorporated into the design. Since the new receiver was not a superheterodyne, the BFO had to track the tuned frequency, providing a 1kc heterodyne which allowed CW to be readily copied. There were a couple of reasons for not designing the new LF receiver as a superheterodyne. First was to allow complete coverage of the tuning range of 15kc to 600kc and second was that fact that the conversion process in a superheterodyne creates a lot of internal noise in the receiver - not a real problem on HF or SW, but a serious determent to good LF performance. At $3000 each, the new RBA receiver was certainly expensive and a look inside the receiver reveals an incredible level of electro-mechanical design and construction. The tuning ranges from 15kc up to 600kc in four bands. The illuminated dial readout is direct in kilocycles along with a two-dial logging scale. The mechanics of the design allow for super-smooth operation of the tuning system. The Gain adjustment controls the sensitivity of the receiver and a gear-driven auxiliary gain control operates from the tuning dial and provides constant gain levels across the tuning range. Two meters are provided, one to monitor Output Level in db and one to monitor the B+ voltage. An Output Limiter is provided for noisy conditions or unexpected strong local signals with the Output Level adjustment setting the output limiter's maximum level. Two levels of selectivity are provided, Broad selectivity is limited to about a 1300kc audio roll-off via an internal LP filter and the Sharp position is provided by a 1kc bandpass filter for CW in noisy conditions or in cases of interference. Audio output is 600 ohms Z and is intended for earphones although the RBA will drive a matched loud speaker if necessary. The separate power supply, CRV-20130, provides the filament voltage and B+ requirements via an armored cable with heavy-duty connectors. The power supply will easily operate two receivers for emergency conditions and two separate connectors are provided. This is the same power supply used for the RBB and RBC receivers. The power supply has a cold-cathode regulator tube (OC3) and a HV rectifier (5U4.) The RBA uses eight tubes, three 6SK7 RF amplifiers, one 6J5 Triode Detector, one 6SK7 BFO, two 6SJ7 AF amplifiers and one 6K6 AF Output.

Federal Telephone & Radio Corporation was owned by ITT and had grown out of the old Federal Telegraph Company that was originally located in Palo Alto, California. FTC's chief engineer was Frederick Kolster, sometimes credited inventor of the directional loop antenna. Lee DeForest was associated with the company at one time. During the mid-twenties, FTC built consumer radios under the "Kolster" brand name. Mackay Radio & Telegraph Company had close ties to FTC and all early Mackay maritime radio equipment was built by FTC. When Mackay was purchased by ITT in 1928, it was not very long before FTC also was added to the growing list of companies owned or controlled by ITT. The purchase took place around 1931 and at this time FTC moved to New Jersey. In New Jersey, FTC continued to build maritime radio equipment, usually for Mackay Radio. Around 1940, Federal Telegraph Company's name was changed to Federal Telephone & Radio Corporation.

The early versions of the RBA receiver are identified as C(FT)-46154 (FT identifies Federal Tele.&Radio Corp. as the contractor) but later versions use CFT-46300 as the receiver identification. Shown in the photo is the CFT-46300 RBA-6 from 1945. This version is identical to the RBA-5 internally but the RBA-6 was rack mount only and was painted Navy gray rather than black wrinkle. The RBA-6 is an impressive performer with ample sensitivity, direct dial read-out with illumination and a tracking BFO rather than regenerative-autodyne detector. The tracking BFO actually works quite well for finding the carrier on NBDs. The dial accuracy is excellent and allows tuning NDBs by frequency rather than constantly referring to charts or graphs. The LP filter does limit the audio frequency response on BC stations but not to the point where the voice is incomprehensible. The OL works quite well at limiting the maximum output and not distorting the signal. The RBA is a first-class longwave receiver capable of receiving any of the LW signals found below 500kc. (See our "Vintage Longwave Receivers" webpage for an in depth article about this receiver.)

Radio Corporation of America - RBB (CRV-46147) and RBC (CRV-46148)

In 1939, the Department of the Navy contracted with RCA to build the ultimate military communications receiver. The design was to replace the aging RAK/RAL regenerative receivers with new receivers of the same rugged construction but with modern performance capabilities. RCA utilized input from engineers from 17 other companies during the design phase of the new receivers. By 1940, the RBA, RBB and RBC were ready for production. The RBA was a TRF LW receiver that matched the RBB and RBC in size and power requirements (and is shown above.) The RBB and RBC were true double preselection superheterodynes using 15 tubes plus a 991 neon bulb voltage limiter in the antenna input, a 6-8B Ballast tube for the Local Oscillator heater and the separate CRV-20130 power supply also used two tubes, a 5U4 rectifier and a VT-105 regulator - 19 tubes in all. The RBB receiver covers 500kc up to 4.0mc in four bands and the RBC covers 4.0mc to 27.0mc, also in four bands. The Local Oscillator's filament is operated from a 17vac tap on the power transformer through the 6-8B ballast tube also the LO's plate is operated from the regulated 105vdc supply. This design effort allowed the RBB/RBC receivers to exhibit very little drift. Three IF amplifier stages were used along with a three step selectivity control, a noise limiter control and a switchable audio bandpass filter. Since the AVC could not be on when receiving CW signals, an Output Limiter circuit could be switched in (CW-OL) to keep static bursts or unexpected strong signals from overloading the receiver or the operator's ears. An adjustable squelch control called a "Silencer" was also included. The construction of the receivers were as much as possible alike allowing many of the same parts to be used for each model. There are some tube and component differences in the preselector section of the RBB/RBC but the IF/AF section is identical for each receiver. Three panel meters provided monitoring of Signal Level in db, Audio Output in db and B+ in volts dc. The audio output was designed for 600 ohm Z earphones and up to 20 pairs could be connected in parallel, (who knows why but that's what the manual indicates.) Some of the later RBB/RBC receivers will have an additional 6AB7 tube installed along with a SO239 connector on the back of the receiver. This was an amplified IF output source generally used for a panadaptor. An internally mounted switch allowed the operator to select this IF amplifier output function if desired. The entire cabinet was mounted to the operating table by four shock mounts.

Unlike the RAK/RAL receivers, the RBB/RBC had accurate direct frequency readout dials that were illuminated and there was also a "power on" pilot lamp. The CRV-20130 power supply was connected via a heavy-duty cable with huge nine-pin MIL connectors. Although the CRV-20130 power supply does provide two connectors to allow operation of two receivers with only one power supply, this was considered as "emergency only" operation. When operating two receivers from one power supply, both receivers will be "ON" regardless of which receiver's power switch is activated. The load of both receivers on one power supply drops the B+ voltage and the filament voltage by about 10 percent but any decrease in performance is only slightly noticeable. Super-smooth tuning with large, easy to read dials that are masked for band-in-use readout make the RBB/RBC series a pleasure to operate. The 600 ohm Z audio output will easily drive a matched loud speaker but the design intent was for earphone operation so don't expect thunderous volume. Sensitivity and selectivity are typical of the best designs of the day.

The 1940 selling price (to the government) for these incredible receivers was $2400 each - a staggering amount of money. An internal examination shows why the price was so high. These rugged, over-built receivers had to withstand the constant mechanical vibration while at sea in addition to the mechanical shock of firing multiple 16" guns (along with firing all of the other artillery present on battleships) and also to hopefully be able to withstand the shock of a possible torpedo or bomb hit and still keep communications operating. Additionally, everything had to have maximum shielding to prevent stray emissions from the LO getting to the antenna and also to allow the RBB/RBC to operate in the presence of other receivers, transmitters and radar without interference. In many instances, the RBB/RBC receivers were so well-respected and their performance so good, they not replaced with more modern receivers until the mid-1960s - a testament to the RBB/RBC's magnificent design and construction. Shown in the photo above is the RBB-2 on the left and the RBC-3 on the right - both built by RCA. 

1944 - National Co. - RAO-7, sn:10

National Company, Inc. & Wells-Gardner Co.  -  RAO Series

National began supplying the U.S. Navy with their NC-100A direct dial readout, coil catacomb band switching receiver as early as 1938. Designated as RAO, the first version is similar to the standard NC-100AX receivers. When WWII began, the Navy wanted minimal radiation from the receiver's Local Oscillator on the antenna. This was primarily to allow the receiver to be used in the presence of other shipboard radio equipment without interference. Beginning with the numbered suffixes, e.g. RAO-1, RAO-2, etc., National added an extra RF Amplifer with an additional coil catacomb and tuning condenser housed in a bolt-on rear chassis and cover. The extra RF Amp provided the isolation necessary to keep the LO radiation on the antenna below the designated level  of <400pW. The RAO circuit uses 11 tubes and tunes AM BC up to 30MC and also features a crystal filter, a tone control and a noise limiter. A 500 Z ohm audio output transformer was incorporated into the circuit as well, though this was standard procedure for Navy receivers and it is likely that the first versions of the RAO also had 500 Z ohm outputs. This was to assure that the B+ did not appear on the speaker terminals as was standard for the civilian National NC-100 series. RAO-2 and some RAO-6 receivers will have an ID from National of NC-120. Most WWII equipment was built under contract and not all RAOs were built by National. Wells-Gardner Company was the second contractor for the RAO series, building the RAO-3, 4 & 5. The Wells-Gardner versions were generally intended for shore stations and are not particularly "heavy-duty military-type" construction. National continued on with the Navy contracts building the RAO-6, 7 & 9 (the designation RAO-8 was not used.) These receivers were of robust construction and had increased shielding to further allow their use with other shipboard equipment without interference. The audio output Z was changed to 600 ohms with the later versions. The RAO-7 & 9 eliminated the S-meter in favor of panadaptor connections. The first RAO-6 receivers had S-meters but later production receivers did not. The later RAOs simplified the maintenance of the receiver by designing the chassis so that it was easily removable from the cabinet (handles were added to the receiver front panel to assist removal.) The cabinet itself was redesigned for better shielding and easier mechanical construction by making it a one piece unit and, though some later cabinets did have lids, most did not. The early RAOs used a separate shock mount system but the new cabinets mounted the shocks directly to the bottom of the cabinet further easing construction and maintenance. The RAO-7 & 9 receivers are physically larger than the earlier versions with full 19" rack width panels although the receivers are not designed for rack mounting. The earlier RAO versions are 17.5" wide, with an integral panel-cabinet-chassis construction that requires major disassembly to service or repair. The RAO receivers have impressive sensitivity and stability although the tuning rate is quite fast which was probably intentional for quick band scanning for signals. The fact that the later RAOs have provisions for panadaptor operation seems to confirm that they were used for surveillance rather than communications.

The receiver shown in the top photo is the National RAO-7 SN: 10. The contract date is Sept. 22, 1943 and the Navy acceptance date is in 9-30-1944. It was stored for many years at the Alameda Naval Air Station in California though it was never installed or put into service. It is in excellent condition and is an all original example that functions beautifully. Shown in the photo to the left is a Wells-Gardner RAO-3 (115vac only) from 1943. I found this particular RAO-3 receiver in 1969. It was a derelict that had been abandoned in a greasy driveway. Most of the tubes were missing and the interior of the cabinet filled with small rocks. I took it home for repair and then used it initially as my first real "ham" receiver making several CW contacts on the 15 meter Novice band. After 37 years of minimal use (mostly storage,) the old RAO-3 has recently undergone another restoration to bring it back to full operation and first-rate appearance (2006.) This is the same RAO-3 was featured in an "Antique Radio Classified" magazine article in the late 1980s titled "Rios Radio Revisited" and it is also pictured in Raymond Moore's book, "Communications Receivers - 4th Ed." under National RAO. Note that the external shock mount is missing as are the military tags on top of the receiver. This is very typical of how the RAO-3 is usually found today leading one to believe that many were never shipped from Wells-Gardner and were "dumped" on the surplus market after the war. 1943 - Wells-Gardner Co. - RAO-3

National Company, Inc. - RBH Series

The RBH was the Navy designation for the NC-156 receiver, a 10 tube superhet that covered 300kc to 1200kc and 1700kc to 17mc in five bands utilizing National's famous moving coil-catacomb bandswitching system. The receiver is a version of the NC-100AX that allowed continuous coverage of the 300kc to 500kc range by having the IF operate at 1500kc (which is why there is a gap in the tuning from 1200kc to 1700kc.) The receiver also features single preselection, two IF amplifiers, crystal filter, S-meter, BFO and tone control. The dial uses the articulated pointer that indicates band in use by its alignment with the proper tuning scale on the illuminated dial. The initial RBH receivers will have "NC-156" on the National Co. nameplate (part of the crystal filter panel.) The first RBH receivers date from around 1940, however the receiver required some modifications for use at sea during WWII and a series of RBH receivers followed. All of the RBH series with number suffixes, e.g. RBH-1, RBH-2, etc., have an additional stage of preselection added with a bolt-in chassis and cabinet to house the additional catacomb section for the coils and an addtional tuning condenser for tuning the stage. This addition was very similar to the RAO receiver change and was for the same purpose of reducing the LO radiation from the antenna (>400pW on the antenna.) The dial system changed on the later RBH receivers, eliminating the articulated pointer and painting the background white rather than silver. The last of the RBH receivers incorporated the same improved cabinet of the later RAO receivers. When operating an RBH today, strong AM-BC stations around 1500kc will resonate with the RBH's 1500kc IF amplifiers and can cause strong heterodynes when tuning in stations or, if the 1500kc AM-BC station is particularly strong, it may dominate the IF system of the RBH. A 1500kc wavetrap on the antenna lead-in will usually cure any serious problem. The early RBH receiver shown in the photo above unfortunately has had all of its Navy tags removed. Sometimes tag removal was a requirement for sales of surplus equipment.

National Company, Inc.  -  RBL-5

National produced the RBL series of longwave TRF regenerative receivers for the Navy during WWII. The RBL uses a seven tube circuit covering 15 KC up to 600 KC in six bands. The tube line up consists of three cascaded 6SK7 RF amplifiers, a 6SG7 regenerative autodyne detector, a 6H6 audio limiter with a 6K6G audio output tube and the 5Y3G rectifier (5U4G in earlier RBLs.) Unlike the RAO that it resembles, the RBL receiver's bandswitch does not operate a moveable coil catacomb, instead an intricate set of gears simultaneously actuates two large ceramic bandswitches. Also unlike many of the WWII longwave receivers, the RBL series has direct frequency readout on the tuning dial. The receiver also included a selectable "broad" or "sharp" audio filter and an adjustable output limiter for operation during intense static conditions. The limiter control was very well designed and works wonders at reducing static bursts. Audio output is via the earphone jack on the front panel and is for 500-600 Z ohm 'phones. Heavy duty construction through-out and the entire receiver is fully shielded with a cabinet that is copper plated under the black wrinkle finish. The RBL-5 shown in the photo is from 1944 and its excellent original condition is matched by its first-rate performance. The RBL-5 is a great performer, capable of receiving NBDs from all over North America, world-wide LW BC, WWVB, JJY, Navy RTTY and almost all other types of signals in the LF spectrum. (See our "Vintage Longwave Receivers" webpage for an in depth article about this receiver.)  

E. H. Scott Radio Laboratories, Inc.  -  SLR-F

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 "Scott Low Radiation" Receiver, or SLR, was built to operate in such a shipboard environment with no interference. It tuned the standard AM Broadcast band and two bandspreaded Shortwave bands. The SLR receivers were designed as a stand-alone receiver capable of high quality reception and wide range audio reproduction via its 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 common. The receiver's output could be distributed throughout the ship via the 600 ohm line. 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. Scott also built the RBO receiver, a similar looking set but without the push-pull audio and 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 with the ship's 600 ohm line. Both receivers were installed in a very large metal cabinet that was shock-mounted to a substantial base mount. Many different versions of these "entertainment" or so called "morale" receivers were built. The receivers were installed not only on U.S. Navy ships but also merchant ships, tankers, transports and other types of American vessels.   

National Company, Inc. - NC-100ASD

National introduced a well designed, direct-reading dial for their NC-100 series receivers in 1938. The "A" version dial had a mechanically articulated dial pointer that indicated the band in use when switching ranges and also added 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 and an optional crystal filter which was indicated by an "X" in the model designation. Around 1938, the Signal Corps wanted the NC-100A with special frequency coverage that included a longwave band. This was provided (200kc to 400kc) but the AM BC band coverage was dropped. The upper bands cover 1.2Mc to 30Mc. Also, the P/P audio was changed to a single-ended 6V6. The Signal Corps also didn't want to use an electrodynamic speaker so a 500 Z ohm output transformer was installed designed to drive a matching 500 Z ohm PM speaker. The designation for this model was NC-100ASD (shown in photo.) The Navy also wanted their own version of the NC-100A - it was designated as RAO - more details above in Navy equipment.

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

1943 - Wells-Gardner - BC-348-Q

Radio Corporation of America  -  BC-348 Series  -  Various Manufacturers

The BC-348 Aircraft Receiver was designed by RCA in the late thirties. It 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.) Some versions will have a 991 neon lamp acting as a regulator on the local oscillator and some versions provide an antenna trim control. 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 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 version) and 1.5-18mc. 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 (usually a BC-375) 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 and the later versions (J, N & Q) with single-ended tubes. Several of the earlier versions were rebuilt into later configurations, especially to add the 200-500kc band. The conversion of the "B" into an "R" is typical of the process. 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 in the 1950s allowing hams the ability to purchase a great performing receiver at a reasonable price - NOS and still in the crate for about $75. The down side is that today it is almost impossible to find a BC-348 that hasn't been modified. Typically, the dynamotor will have been removed 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.) Many other dubious mods were published in various surplus conversion books of the day that did compromise the BC-348's performance. Additionally, many hams would drill the case with lots of .25" holes thinking the receiver needed extra cooling. Originally, the BC-348 operated at altitudes up to 25,000 feet where the temperature inside the aircraft was below zero - cooling the receiver was not a problem. But even on the ground in other applications, the BC-348 didn't run hot and adding ventilation holes will only ruin the cabinet. A great performing receiver when conservatively modified (AC PS only) and accurately aligned. Shown above is a 1943 Wells-Gardner version BC-348-Q. Other variations include, the BC-224, which was a 12vdc version used for earlier aircraft electrical systems. Its external appearance is identical to the BC-348.

See next listing for the actual use of the BC-348-Q receiver in a working environment...

SCR-287  -   B-17 Bomber Radio Station

BC-375-E - General Electric Corp. &  BC-348-Q - Wells-Gardner Co.

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. Though the BC-375 was designed in the early thirties and built from the mid-thirties on up to mid-WWII, it found a long-term usage with the Signal Corps due to its ease of operation and reliability.  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.) 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.

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 console 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. 

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 rebuild the BC-375 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.  Most of the BC-375's bad rap came from hams expecting a military aircraft transmitter to work like a ham transmitter, so improperly designed, inadequate power supplies and modifications to the original design concept were considered the standard solution. Though TVI was a problem in the fifties, today's strong TV cable and satellite dish signals are not affected by the BC-375 operation. The transmitter's stability depends on the frequency of operation and most problems arise as the frequency of operation is pushed above 4.0 MC. For more details on successful operation of the BC-375-E "on the air" go to this short article - Using the BC-375-E Today 

1943 - Farnsworth BC-342-N

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

The BC-342 is part of a series of receivers that includes the BC-312, BC-314, BC-342 and the BC344 receivers. These are stoutly built receivers that make use of extensive shielding utilizing steel sheet metal rather than aluminum (although the earliest versions do use mostly aluminum construction.) 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 intention of use within a building installation or mobile use with AC generator. The huge connector protruding out of the front panel allows power input on DC versions or filament voltage access on AC models, telegraph key, PTT and microphone routing, stand-by in DC versions, audio outputs and antenna relay function for interfacing with transmitters and other equipment. There are several variations for each model in the series with some receivers having Crystal Filters installed, some have selectable audio output 250 ohms Z or 4K ohms Z, some also allow access to the 1st AF output for earphone operation along with many other subtle variations depending on when the receiver was built. The BC-342 series of receivers were used extensively in ground applications from just before WWII up into the 1950s.

If you are planning to restore one of the BC-312/342 family of receivers, be aware that the mechanical design of the receiver does not consider ease of maintenance beyond changing tubes and routine alignment. The receiver is difficult to disassemble, requiring the unsoldering of several connections just to remove the front panel. Dismounting any of the assemblies is arduous. 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. It is routine to have to dismount several parts or assemblies just to access other parts for removal. Any serious restoration work is sure to result in several large piles of sorted screws and other parts before reassembly can begin. The laborious restoration work will be rewarded however, as the BC-312/314/342/344 receivers are excellent performers with great sensitivity and plenty of audio when driving a matched speaker. Shown in the photo 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. 

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.) Sometimes this receiver is called the "Airborne S-36" based on its similarity to Hallicrafters' VHF base receiver, the S-36.

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.

Mackay Radio & Telegraph Co.  -  Type 105-A
Contractor: Federal Telegraph Company

Mackay Radio & Telegraph Company was founded by Clarence Mackay, son of John W. Mackay, one of the "Big Four of the Comstock" fame here in Virginia City, Nevada. John Mackay initially made his fortune in Comstock silver but he later (1883) moved into telegraphic communications. Mackay, along with J. Gordon Bennett Jr., formed several telegraph communications companies to compete with Jay Gould's Western Union. Postal Telegraph Company (1886) was the best known, along with Commercial Cable Company (1884). Eventually, these companies, along with other Mackay-Bennett telegraph companies, had transoceanic cables across both major oceans. When John Mackay died in 1902, Clarence inherited the businesses. Clarence Mackay saw to the completion of the transpacific cable in 1904. Radio was added to the business end of things in 1925 to provide "radiogram" service to every area of the world. Mackay Radio was mainly interested in maritime communications which went along with the maritime radio-telegraph business. By 1928, ITT had merged with most of Mackay's business interests but the Mackay name continued on for several decades. Today, Mackay Communications is still doing business, located in North Carolina.

Federal Telegraph Company started out in Palo Alto, California mainly dealing in arc transmitters. At one time, Lee DeForest worked for the company but Frederick Kolster was the head engineer for most of FTC's history. FTC bought Brandes and created a division called Kolster Radio Company for selling consumer radios in the mid-twenties. FTC became involved with Mackay Radio in 1926 when Mackay bought a radio station that had belonged to FTC. When Mackay sold his interests to ITT, then Federal Telegraph was contracted to do most of the Mackay Radio work. Federal Telegraph moved to New Jersey in 1931 when it was purchased by ITT. For awhile ITT tried the consumer radio market with Kolster International but it was a short-lived venture. The name of Federal Telegraph Co. was changed to Federal Radio and Telephone Company around 1940.

The Type 105-A is actually a pre-WWII commercial shipboard receiver that dates from sometime after the Federal Telegraph move to New Jersey since the ID tag lists Newark, N.J. as FTC's location. It is a four tube receiver using five-pin cathode-type tubes. It is possible to use type 27 or type 56 tubes and with an increase in the filament voltage, type 76 tubes could also be used. It is possible that this Type 105-A was updated either at the factory or by a professional radio work shop for the cathode type tubes since there are some indications that the original design may have used direct-heated filament type triodes. The frequency coverage is 1500kc down to 15kc in seven tuning ranges. Power is supplied by batteries. Like earlier designs for shipboard receivers, e.g. the IP-501-A, the Mackay 105-A utilizes an LC Antenna tuner ahead of the regenerative detector to increase gain and selectivity. An Antenna Series Condenser switch selects various value capacitors to match the ship antenna to the receiver input and a stepped Tone control provides some relief from static. The panel meter is a dual meter that normally reads filament voltage but B+ voltage can also be monitored by activating a panel switch. The left large tuning knob tunes the Antenna Condenser, the middle large knob controls the Regeneration Condenser and the right large knob tunes the Detector Condenser. The Mackay 105-A is built for shipboard use being physically stout and very heavy. Originally the receiver was panel mounted in one of the Mackay Marine Radio Units that housed the majority of the radio gear for the ship. (See our "Vintage Longwave Receivers" webpage for an in depth article about this receiver.)

Mackay Radio & Telegraph Co. - Type 102-B Frequency Monitor   Shown in the photo to the right is an accessory piece of test-monitoring equipment for shipboard operation, the Type 102-B Frequency Monitor. This device works something like a heterodyne frequency meter. A small antenna would be connected to the binding post terminal on the front panel (top-center.) This antenna can act as a pickup or a radiator depending on the operator's intentions. Internally, the 102-B has a type 76 oscillator feeding a type 6C6 buffer. These stages then capacitively feed the tank circuit of a type 76 broadly tuned RF amplifier whose input grid is connected to the antenna post and whose plate output is capacitively coupled to the telephone jack on the front panel. When it is desired to monitor or test a transmitted signal, the operating frequency can be determined as a heterodyne beating with the internal oscillator heard on 'phones plugged into the phone jack. Since most shipboard transmitters in the thirties operated CW or MCW, the operator could also monitor the transmitted signal for other characteristics or suspected problems. When it was desired to test a receiver, the internal oscillator-buffer of the 102-B emits a small amplitude signal from the small antenna which can be received and beat with the receiver's tuned frequency to determine the actual received frequency. Frequency coverage is from 5.5MC up to 16.5MC. Built by Federal Telegraph Company, the Type102-B is stoutly built into a steel cabinet. The airplane-type dial is not illuminated since the entire device runs on batteries. There is a power cable access hole on the right side of the cabinet. Dates from 1938.

1950 Signal Corps R-320/FRC aka RCA SC-88

Radio Corporation of America  -  AR-88 Series

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

RCA's greatest receiver creation was the AR-88. Designed in 1941 by Lester Fowler and George Blaker, it 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.) Much of the production ended up in England, Canada or Russia because of WWII Lend-Lease. The AR-88 was used extensively at Bletchley Park for successful intercept work during WWII (along with National HRO receivers.) RCA and Radio Marine Corp. of America also used the AR-88 in many of their own installations for various purposes. The AR-88 series receivers all use three stages of IF amplification with stagger-tuned IF transformers. Two under-coupled IF transformers and two over-coupled IF transformers are utilized. This usually requires a sweep generator and oscilloscope for proper alignment, however there is a procedure to align the IF section using just a VTVM but the results are 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 an S-meter incorporated into the circuit however many AR-88D receivers did not have S-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 an S-meter, if they became available.

Many of the AR-88 receivers were used in Triple Diversity Receivers like the DR-89 - a seven foot tall rack loaded with three AR-88s and all of the auxiliary equipment necessary for professional diversity reception. The Navy designation for the DR-89 was RDM. The Diversity AR-88 receivers did not have S-meters installed because the Diode Load from each receiver was connected to the three Output Meters that were installed in the Monitoring Unit Panel of the DR-89/RDM rack. All Diversity AR-88 receivers will have a "DIVERSITY IF GAIN" control on the front panel for balancing the three receivers in the rack using a test signal. This provided an adjustment for equal diversity effect even if the receivers were not identical in their performance. Later DR-89/RDMs used updated versions of the AR-88 designated as the CR-88. The U.S. Army Signal Corps had their versions of the Triple Diversity DR-89 with the military ID of OA-58A/FRC. It used a slightly different, upgraded receiver, i.e., the SC-88. The AR-88D doesn't have the "DIVERSITY IF GAIN" control and was always installed into a table cabinet. A matching speaker was available. The AR-88LF and CR-91 were versions with a VLF band in place of the AM-BC band. The AR-88 series was produced from 1941 up to around 1950.

The AR-88 series of receivers are well known for their incredible performance but a great many AR-88s have led a hard life and are nowadays found in "rough" condition with missing shields or other more serious problems. Many are found as victims of careless repairs or needless modifications. A well-cared for AR-88 that has not been modified and has been aligned correctly will have tremendous sensitivity and flawless audio reproduction. 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 accuracy is vague. The AR-88 receivers are heavy, weighing in at nearly 100 lbs. Shown above is one of the last of the AR-88 versions, the SC-88, (Signal Corps designation R-320/FRC, SN 214), from 1950, featuring "band-in-use" masking and the crystal phasing control on the front panel (the AR-88's is internally adjusted.) The total production of SC-88 receivers was quite small with estimates usually being around 300 receivers built.

Mackay Radio & Telegraph Company  -  Type  3001-A

The Mackay Radio & Telegraph Co. Type 3001-A is a Longwave regenerative receiver covering 15kc to 640kc in four bands and dates from as early as 1948 but with most manufacturing dating much later. The 3001-A was mainly for commercial shipboard (non-military) use where it could be set up as the main receiver or as the emergency receiver. The receivers were sometimes installed in the Mackay "Marine Radio Units," like the MRU-19/20, a shipboard radio console which contained two 3001-A receivers along with transmitters and other auxiliary equipment (the MRU receivers were panel mounted.) The 3001-A uses an AC-DC circuit and can operate on 115vac or on batteries. Various filament battery options were available with 6vdc, 12vdc and 24vdc being the most popular. B+ was supplied by standard dry cell B batteries when used. The receiver uses a four pin Amperite ballast tube along with six octal tubes. A small built-in speaker provides for radio room monitoring but earphones would normally have been used by the shipboard radio operator. The purple (when illuminated) dial provides a unique visual experience when tuning in the various signals. Selectivity is controlled by a combination of the RF Gain setting and the setting of the Regeneration. The 3001-A is very sensitive and capable of receiving any of the NDBs and other LW stations found in the spectrum below 500kc. These type of Mackay receivers were in use for several decades and were commonly found still operating on commercial ships as late the 1990s. These receivers also likely date from after the purchase of Federal Radio and Telephone Co. by ITT which consolidated Mackay Radio and Federal Radio under ITT ownership. (See our "Vintage Longwave Receivers" webpage for an in depth article about this receiver.)

1950 Collins 51J-2

Collins Radio Co. - 51J Series

Introduced in 1949, the 51J series was developed as a general coverage receiver primarily for military, commercial or individual use providing accurate frequency readout and great stability. The receiver utilized a permeability tuned double conversion circuit with the 70E-7 PTO in a dual tuned IF system and a multiple frequency crystal oscillator to cover .5mc to 30.5mc in thirty (1mc wide) bands. Dial accuracy is maintained at 1.0kc throughout the tuning ranges by limiting the coverage of each band to 1.0mc. Band 1 actually is triple conversion but only to allow coverage of the AM BC band. Bands 2 and 3 are single conversion while all of the remaining bands are double conversion. 16 tubes are used in the 51J-1 and J-2. The ham bands are high-lighted in green on the megacycle drum dial but, at nearly $900, not many hams could afford a 51J as their station receiver. Early versions have a metal dial bezel, the Collins' "winged emblem" and an illuminated S-meter. Audio response is restricted at 200 to 2500Hz and is definitely not high fidelity, usually sounding somewhat "muffled" when receiving AM voice signals. In 1952, the 51J-3 was introduced, featuring an 18 tube circuit (adding a voltage regulator and vfo buffer,) a new version of the PTO (70E-15) and eliminating the 300 ohm Z antenna input (by removing the primary winding on the antenna coils) and redesigning the antenna input to a more flexible design with antenna trim control. This revision was at the request of the Signal Corps, who wanted to use the 51J receiver for their teletype installations but found the fixed 300 ohm Z antenna input requirements difficult to work with as most of their installations used Lo-Z vertical whip antennas. The military had their version of the 51J-3 designated as the R-388 and it was built from 1952 through about 1955. In 1955, the 51J-4, with 19 tubes and mechanical filters, became available and was offered up to about 1964.  The 51J-4 and R-388 are the ultimate evolution of the design but the earlier 51J-1 and J-2s have their own appeal and top-notch reception for most modes of transmission. Shown is an early 51J-2 from 1950.

If you are working on a 51J-2 receiver be aware that the 1950 version of the 51J-2 manual is fraught with errors, especially in the receiver alignment section and the component identification layouts. As to the 51J/R-388 performance overall, most of the 51J/R-388 receivers were used for data reception such as RTTY where the severe audio limitations made sense. For AM BC reception and SW BC reception the receivers are somewhat disappointing in their limited audio reproduction. There are also issues with the AVC circuit which never seems to function very well. Dial accuracy and stability - both necessary for RTTY work - were the 51J selling points to the Signal Corps and still are the 51J's primary attributes today.

1953 Hammarlund SP-600 JX-21

Hammarlund Manufacturing Co., Inc.  -  SP-600 Series

Introduced in 1950 and selling for nearly $1000 at that time, the SP-600 was intended for the military and commercial user market. It was a very popular receiver and many thousands were built, especially for military applications. Though most versions were built throughout the 1950s, the SP-600 continued to be produced in smaller numbers up into the early 1970s. The standard SP-600 tunes from .54 to 54MC in six bands. A "J" suffix indicates JAN parts were used in the construction and an "X" suffix indicates a switchable crystal LO. Hammarlund also offered a "JL" version with 100-400KC substituted for the .54-1.35MC band and a "VLF" version that covered 10-540KC. Hammarlund made over 40 variations that were assigned a numerical suffix which identified the particular circuit, mechanical changes or sometimes the end-user. The last in the "time-line" was the model variation SP-600 JX-21A from 1969-1972 which utilized a product detector circuit, two additional tubes and some other changes to make it "compatible" with SSB operations.

Most versions use a 20 tube double conversion superheterodyne circuit with a rotating turret bandswitch. The receivers also feature enormous proportions, robust construction and oversize controls - along with a super-smooth tuning system that only adds to the enjoyment of operating these fine receivers. Double conversion is switched in above 7.4MC and uses a crystal controlled conversion oscillator. Though the SP-600 has two dials, it has no bandspread - the right side dial is a logging scale allowing precise retuning of desired stations. On the left is the main tuning dial and the mechanically articulated dial pointer that indicates which tuning scale is in use (along with the small window between the dials that shows which tuning range is selected.) The tuning arrangement was an up-dated version of the "Continuous Bandspread" system introduced in RCA's AR-88 series receivers in the 1940s. The frequency readout accuracy is vague which is why a precise logging scale system is incorporated into the SP-600 design. The S-meter is not illuminated and a switch is provided to indicate either carrier level or audio output. Most (but not all) SP-600 model numbers usually will have a suffix with "J" or "JX" followed by a numeral. As mentioned above, suffix "J" indicated that, as much as possible, military level components and construction were used. Suffix "X" indicated that a switchable six-position, fixed-frequency crystal-controlled oscillator was installed that allowed the user to install HC-6/U type crystals for specific desired LO frequencies. The user could switch to any of the crystal LO frequencies for increased stability for that particular frequency - however, the receiver still has to be "tuned" to the desired frequency for the RF and Mixer stages to be in tune. Many SP-600 receivers were set-up for diversity operation and the standard diversity model was the JX-17 version. This version was produced in large numbers and can be easily spotted by observing that it has two extra controls and uses three red colored knobs. The SP-600 Audio output is about 2 watts from a single 6V6 using a balanced split-winding audio output transformer for 600 ohms Z. The audio quality from a rebuilt SP-600 is impressive.

The number following the letter suffix generally indicates specific features for that version, e.g., contract or end user, circuit upgrades, etc., with the number ranges being more or less chronological until the last of production. Though the number suffixes were more or less chronologically assigned, many of the versions were built over a fairly long time period. This meant that engineering and component changes were being added as receiver production continued. The end result today is that there are early and later versions of many of the numbered suffix models and documentation is not always specifically accurate based just on the number suffix. It is more accurate to use the build date of the receiver and use documentation that is dated close to the receiver manufacture date. 

All early versions of the SP-600 receivers were built using molded tubular capacitors of various manufacture - Cornell-Dubilier (most common) and Sprague (sometimes) are the types encountered. Nearly all molded capacitors are defective nowadays, requiring extensive replacement work when rebuilding an SP-600. In fact, it's quite common to find a few burned resistors in an un-rebuilt SP-600 due to leaky or shorted molded tubular capacitors. Later versions had more reliable ceramic-disk type capacitors installed rather than the problem-prone molded capacitors. All early SP-600s will require a rebuild for the receiver to operate at the high level of performance that it is capable of. Molded capacitor replacement requires some major disassembly of the various units in the receiver. The turret bandswitching assembly has 6 capacitors inside, the RF platform has 20 capacitors inside, the IF transformers have 1 or 2 capacitors inside, T1 has 1 capacitor inside and the conversion crystal oscillator has 3 capacitors inside - all these units have to be partially disassembled to access these molded capacitors that need to be replaced. The JX versions will have the switchable crystal oscillator that also needs rebuilding. Additionally, there are many other molded capacitors under the chassis. Most SP-600s will have over 50 capacitors that will need replacement - a challenging task but well worth the effort required. After a rebuild, the SP-600 will need a full IF-RF alignment for a performance level that meets or exceeds original specifications. For more details on rebuilding the Hammarlund SP-600 receiver, read our article - "Rebuilding the Hammarlund SP-600" - navigation link at the bottom of this page

It is interesting to note that Hammarlund did not refer to the SP-600 as a "Super-Pro" receiver in their manuals and only occasionally is its "Super-Pro" lineage mentioned in Hammarlund advertising. The photo above shows the SP-600 JX-21 version from 1953 installed in an original Hammarlund SP-600 cabinet. The JX-21 was generally used by the USAF. This is the early version of the JX-21 - so it does not have the product detector SSB changes. The photo below shows the SP-600-25C built for the US Army Signal Corps and it is also housed in an original SP-600 cabinet. The SP-600-25C version has the 25-60 cycle power transformer and does not have the switchable crystal oscillator ("X" option.) SP-600 cabinet colors vary from dark charcoal to light gray depending on when they were manufactured. A rebuilt SP-600 is a pleasure to operate with incredibly smooth tuning, competitive sensitivity, a great selectivity set-up featuring six positions that include three crystal filter positions and, of course, its fabulous audio - but, if you're looking for a "to the kilocycle" accurate frequency readout and you're willing to sacrifice audio quality,...well, maybe you'd want something by Collins instead.

1953 Hammarlund SP-600-25C

1951 Collins R-390/URR in a CY-979/URR cabinet

Collins Radio Co.  -  R-390/URR & R-390A/URR

Arguably, the R-390/URR and its later kin, the R-390A/URR, are the ultimate tube-type receivers. The first version of this incredible receiver was the R-390 featuring 33 tubes (includes the 3TF7 ballast tube,) double or triple conversion, two RF stages, six IF stages, modular construction, three audio filter settings, six selectivity bandwidths and frequency coverage from 500 kc. to 32.0 mc. in 32 - one megacycle wide - bands. It is a high performance receiver that really "shows its stuff" when conditions are poor but will also provide fairly nice audio quality when receiving conditions allow for it. The most common complaint is the cumbersome tuning that, while "parked" on one frequency is not apparent, shows up when spanning an entire band or changing ranges. Most of the "stiff tuning" complaints can be traced to an over accumulation of grease and dirt in the gear train. When clean and properly (lightly oiled) lubed, the tuning is very light and easy to manipulate. Only Collins or Motorola built the R-390 contracts which ran from 1951 through 1953. The military complained that the R-390 was very difficult to maintain and too expensive. Some of the maintenance issues involve the R-390's elaborate electronically regulated B+ circuit that uses two 6082 tubes along with two 5651 voltage reference tubes and a 6BH6 DC Voltage Amplifier tube. This circuit runs quite hot and accounts for many of the problems that develop in the audio module (where the regulator circuit is located.) Additionally, the R-390's gear train has a moveable "locking gear" that must be installed prior to removing the RF module (if you want to keep everything synchronized.) This gear was painted green and usually mounted with a screw on the front of the gear box. Each time the RF Module is removed and then replaced on an R-390, the KC and MC drive shaft split gears have to be reset for backlash, the Crystal Oscillator module's bandswitch has to be synchronized and the oldham coupler installed. Removal of any of the crystals in the Crystal Oscillator module requires removal of the hard-wired crystal oven. When the military complained about complex maintenance issues, they weren't exaggerating.

Collins designed a replacement receiver that was introduced in 1954 with the designation of R-390A/URR. Though the new receiver looked very similar externally to the R-390, inside numerous changes were made to improve cost-to-performance and ease of maintenance. The new receiver's gear box was removable as a unit and synchronization would be maintained, the crystal oven just plugged into the Crystal Oscillator module (it is secured by screws though,) the B+ voltage regulator circuit became a standard 0A2 tube, the crystal calibrator was combined into the RF module (eliminating the separate Crystal Calibrator module of the R-390) and the Crystal Oscillator module was mounted to the RF module so removal of the entire RF deck kept everything synchronized together except the PTO. Most of the maintenance "quirks" of the R-390 were corrected in the R-390A. The major performance change involved the installation of four mechanical filters in the IF section of the receiver. The steep slopes of the mechanical filters gave the R-390A excellent selectivity on 16KC, 8KC (really about 11KC,) 4KC and 2KC bandwidths. The 1KC and .1KC bandwidths are crystal filter derived from the 2KC wide setting. The R-390A uses 26 tubes (including the 3TF7 ballast tube) with one RF stage, four IF stages, mechanical filters on four of the six selectivity positions, plus an 800Hz audio filter. When properly set-up, one can dig right through the QRM while maintaining fantastic sensitivity making the R-390A one of the finest tube-type receivers ever built. However, some ham AM operators find the audio on an R-390A to be a bit harsh due to "ringing" in the mechanical filters. The R-390A was produced in yearly contracts from 1954 up through 1967 (and a very small contract in 1984) with many different contractors building the receivers during those years. Though the R-390A's six modules and redesigned maintenance approach made field repairs easier, it was still a complex receiver. Though the military wanted a less expensive receiver, it certainly wasn't that either.

The R-390 and R-390A receivers have provided reliable communications under adverse conditions for years and even though the designs are over 50 years old, they are still one of the best tube-type receivers around. Many R-390 and R-390A receivers are still being used today, some in professional applications, but also for serious SWLing and, of course, in vintage ham stations around the world. Many AM operators prefer the R-390 version for its better over-all sound quality when listening to SWBC or AM stations in general, however one must consider the maintenance challenges when selecting the R-390 for a station receiver. Nowadays, many R-390 and R-390A receivers are being used in "as purchased" condition - that is, the receiver has not been thoroughly serviced and properly aligned (or is it "alined?") The performance of a fully functional, freshly serviced and recently aligned R-390/390A is incredible. The top photo shows our 1951 Collins R-390 housed in an original 1955 CY-979/URR aluminum table cabinet. The bottom photo shows our 1955 contract (built in 1956) Collins R-390A. Who knows what the "37.4" stencil means?

1955 Collins R-390A (built in 1956) 

Nems-Clarke (Vitro Electronics) - 1306-B Special Purpose Receiver

Allen Clarke started in the electronics design business in the 1940s and by 1951 had a small electronics design business. NEMS was an acronym for National Electric Machine Shops, a name chosen by NESCO, National Electric Supply Company, when they incorporated in 1937. NESCO goes back to 1899 and the company was involved in radio manufacturing very early with many contracts assigned to them in WWI and after. NEMS and Clarke merged in 1955 as Nems-Clarke - specializing in high-end commercial-military radio equipment. The company was purchased by Vitro Electronics in 1957. Nems-Clarke produced Special Purpose Receivers for surveillance and telemetry that were used throughout the fifties and sixties. All(?) of their receivers operate in the VHF and UHF ranges. The 1306-B Special Purpose Receiver is a 29 tube AM-FM-CW receiver that was usually operated with a SDU-200-6 Spectrum Display Unit (panadaptor.) The receiver tunes 30mc to 60mc and 55mc to 260mc with separate dials for each band that are only illuminated when in use. Selectable IF bandwidths, selectable IF AGC/Manual Gain controls, Squelch and a BFO with variable Pitch Control are provided. The zero-center meter provides accurate tuning for FM signals while the right hand meter measures signal strength. The built-in speaker is a very small "communications quality" unit that is located behind the screened cover. A 600 ohm audio line is provided on the rear panel can provide excellent audio quality to a matched loud speaker. The "SPEAKER" switch is a factory modification that replaced a PHONE jack with a switch to silence the panel speaker. Many of the Nems-Clarke surveillance receivers were used to monitor Russian missile launches and analyze data transmissions along with any voice traffic. The 1306-B is a great performer with an impressive appearance.

Technical Materiel Corporation  -  GPR-90, R-825/URR

Technical Materiel Corporation, or TMC, was founded in 1934 by Ray DePasquale and, by the early 1950s, had become a major supplier of receivers, transmitters and accessories for the military and for commercial users. TMC introduced the GPR-90 communications receiver in 1955 with a selling price of $395. The circuit used 15 tubes and provided several unusual features, such as a three-position audio filter with adjustable audio bandwidth (on 1200~ position,) the multi-impedance output taps on the audio output transformer (4, 8, 16 and 500 ohms Z) and a great performing, wide range crystal filter. The circuit also featured two RF amplifiers on bands 3, 4, 5 and 6 (3.3mc - 31.5mc) along with double conversion on bands 4, 5 and 6 (5.4mc -31.5mc.) The first RF amplifier is a grounded-grid configuration with a wide-band input transformer to allow both 75 ohm Z and 300 ohm Z input impedances over the entire tuning range of the receiver. The cabinet was painted an unusual dark blue wrinkle finish and had an easily removable top lid for access to the top of the chassis. After the first year of manufacture, a 100kc crystal calibrator was installed and the selling price increased to $495. The military used the GPR-90 and identified it as the R-825/URR.

The GPR-90's performance has been a source of controversy for many years and it is common to find diverse reviews, some "panning" the receiver as "lacking sensitivity" or "not up to TMC standards" while others praise its reliability, great audio quality, impressive styling and overall competitive performance. When a GPR-90 has been well-cared for and it is in good operating condition with a recent alignment, it is a superb performer with fabulous audio reproduction, highly adjustable selectivity and tremendous sensitivity. The Crystal Filter in the GPR-90 is the best performing crystal filter of any communications receiver. TMC addressed the issue of "not to the kilocycle accurate" dial readout in a 1956 Sales Service Information sheet (SUP-1 GPR 9-56) that stated, "People who require frequency meters should buy frequency meters - not make them double as communications receivers." Obviously a humorous "slam" against the competition (Collins.) The GPR-90 shown is an early version (without the crystal calibrator) from 1955. The GPR-90 was built from 1955 up to 1962. TMC is still in business today and, although the company is very small, it is run by Neil DePasquale, son of the original founder.

For some reason, many of the GPR-90 critics want to compare this $400-$500 receiver to the $2200 (1967 price) R-390A receiver. The design concept of these two receivers couldn't be more diverse and a comparison simply isn't valid (other than to illustrate what can be designed and built when the end-cost is not an issue.) A more comparable receiver would be the Hammarlund HQ-180 - a receiver that was similar in design, construction and performance. In fact, the GPR-90 even bares a physical resemblance to some of the Hammarlund "HQ" receivers.

National Company Inc.  -  HRO-5TA1 

At the end of WWII, most manufacturers had been building for the war effort since 1942. They didn't have anything new or ready for production for the 1946 model year. National offered the HRO-5TA in 1946 as their new table model receiver. The HRO Senior had evolved through WWII but by the end of the war, it still didn't look very different than the old pre-war receiver. The major changes during the war involved the crystal filter design, the switch to metal octal tubes and the use of mostly JAN parts. The 1946 coil sets now used a single aluminum plate with silk-screened graphs and the toggle switch functions were now identified (these toggle switch IDs were actually on the late WWII models also.) The first HRO-5TAs were nearly the same as the late WWII receivers except for the return of the amateur bandspread function to coil sets A,B,C and D. In a short time, the HRO-5TA1 replaced the TA and added a noise limiter to the circuit. The TA1 used 12 tubes - two additional tubes were necessary for the noise limiter circuit. Early versions of the TA1 will have the round S-meter but a square S-meter was used on most of the production. Unbelievably low noise in combination with high sensitivity and incredible bandspread make the HRO-5TA1 one of the best receivers for a vintage ham station. Of course, the micrometer dial (while super-smooth for tuning) does not allow for accurate frequency read-out, but in 1946, most hams had a Frequency Standard (a 1.0mc./100kc. xtal. oscillator) in the shack and many were still using crystal controlled transmitters. As always, the accurate resetting ability of the micrometer dial was unbeatable. When set up for bandspreading, the micrometer dial tunes each ham band in 400 divisions, or the equivalent of a linear dial nine and a half feet long. Though the HRO-5TA1 is an excellent ham band receiver, it isn't found in too many vintage ham stations these days, probably because it requires several accessories and the dial readout must be correlated with graphs to determine tuned frequency. Additionally, it uses a single-ended audio output, the dial is not illuminated and the receiver has a rather basic appearance.

The Hallicrafters, Inc.  -  S-38 Series

The S-38 was a post-war continuation of the "introductory" type receiver line, characterized by the pre-war Sky Buddy series. Intended for the beginning ham or shortwave listener, the S-38 was low-priced, easy to operate and most users were able to get good performance results considering the receiver's circuit limitations. Introduced in 1946, the initial S-38 had six tubes with Bandspread, BFO and Noise Limiter circuits. All of the S-38 series receivers were AC-DC operated. Shortly after its introduction, the circuit was changed to a five tube set with no noise limiter and a CW position that actually set-up a regenerative oscillation in the IF. Versions A, B and C have semi-circular dials while the D and E versions have slide-rule dials. Selling price was around $40 in 1946 but by production's end, in 1961, the price had climbed to $55.

The Hallicrafters, Inc.  -  SX-42

The SX-42 was introduced in mid-1946 as the post-war successor to the company's former "flagship" - the SX-28A. The SX-42 was a complete departure from the usual receiver styling of the time. Well-known industrial designer Raymond Loewy created a receiver exterior that didn't look like any piece of radio gear that had proceeded his futuristic, award-winning design. The main tuning escutcheon with its green tinted plastic and green main tuning dial resembled something from under a then modern jet canopy. A coaxial tuning system allowed the user to "lock" either the main tuning or bandspread tuning depending on which was going to be used. Besides the ultra-modern exterior, the receiver circuit boasted a very wide frequency coverage of .54 to 108MC with the addition of Frequency Modulation capabilities from 27 to 108MC. The receiver used 15 tubes like its predecessor the SX-28A did but a Converter tube is used rather than separate LO and Mixer tubes. Additionally, a VR tube was included along with Limiter and Discriminator tubes for FM. The SX-42 was single-conversion with double pre-selection on all bands (except band 1, AM-BC) using two seven-pin miniature tubes for RF amplifiers (6AG5 tubes.) Four Loktal type tubes were also used in the circuit and the remaining nine tubes were standard Octal types. The audio circuit used P-P 6V6 tubes and provided 500Z ohm and 5000Z ohm outputs. Selling price was $250 but, by 1947, the price increased to $275. There were several matching speakers available but the R-42 table-top bass-reflex speaker is generally pictured with the receiver in Hallicrafters' advertising. Another accessory was a table top "Tilt-Mount" on which the receiver was placed. The Tilt-Mount then allowed the entire receiver position to be moved in any angle to allow a comfortable view the receiver front panel.

The SX-42 was really never a very popular receiver with hams. Certainly the expense of the receiver was an important issue for many but its unusual looks, which hams may have been considered "too modern" in the then age of "wrinkle finish black panels," may have also been a factor. The coverage of the then new FM band (88 to 108MC started in 1946) may have made hams feel that the receiver was more of an expensive luxury for the well-to-do consumer than for a typical budget-minded ham. At any rate, production of the SX-42 was stopped in early 1948 - a fairly short lifespan for a "flagship" receiver. The SX-62 took the SX-42's place as the high-end Hallicrafters receiver but it seemed to again be more for the consumer market and few hams bought them as their station receiver. The popular SX-71, certainly designed for hams, filled in that portion of the ham communications receiver market after the demise of the SX-42.

Today, the features that resulted in the SX-42's only moderate success are what attract collectors to the receiver - the futuristic styling (which won an International Design Award for Raymond Loewy from the NY Museum of Modern Art,) the wide-swing FM-BC coverage, the fabulous audio (when using the proper Z speaker) and the receiver's scarcity all contribute to the SX-42's desirability. Additionally, the SX-42 in featured in a plethora of late-forties "B" movies, from Gene Autrey shows to low-budget science fiction movies, so SX-42 fans can regularly spot their favorite receiver in a multitude of film backgrounds. NOTE: A better photo is coming as soon as I restore the cabinet. Painting is difficult when the temp is below 30 and the snow is flying.

Collins Radio Co.  -  75A-1 

Art Collins began selling amateur transmitters in the early thirties. High quality and great performance brought in commercial and military customers making Collins Radio a major supplier of radio equipment during WWII. Collins entered into the communications receiver market after WWII with a double conversion superheterodyne receiver that was entirely permeability tuned. Using a precision Permeability Tuned Oscillator (called a PTO - Type 70E-7) along with a multiple crystal controlled oscillator and by keeping the maximum coverage of each band to just 1.0 MC, Collins was able to achieve 1.0 KC accuracy in the dial read out with receiver stability that was incredible. The linear dial system features "band in use" illumination and requires twelve #328 lamps - two lamps for each band. The 75A was an introductory model that was probably not produced in any quantity. It was superseded by the 75A-1 in 1947 - the only noticeable difference was the addition of a Noise Limiter circuit with a front panel switch. Though the 75A-1 is a 1947 design, the receiver's performance is a pleasant surprise - more like a receiver from the 1960s with impressive stability, dial accuracy, sensitivity and selectivity. The 75A-1 is a first-class receiver for a vintage ham station with performance that is still competitive, even on 10 meters. Audio in the AM mode may be considered somewhat restricted due to the 75A-1's excellent selectivity but, after all (using the CCA argument,) it is a communications receiver.

Collins Radio Co.  -  32V-2

The 32V-2 transmitter was introduced in 1948 and had some improvements over its predecessor, the 32V-1. The new transmitter redesigned the Pi-network so that it could be fully adjusted with the front panel controls. The V-1 design required lifting the lid to access the loading adjustment. There were other minor improvements to the power supply and regulation during the production of the V-2. The transmitter uses a PTO and multiplier stages to create a tracking exciter that allows the transmitter to stay "in tune" as the frequency is changed. All that is required is for the operator to set the frequency and then "match" the transmitter output to the antenna. Other than the Pi-network, all circuits are automatically tuned as the tuning dial is adjusted. The system used the typical Collins coil-slug rack carriers and full permeability tuning is used throughout the oscillator and multiplier stages. The frequency readout is Collins-accurate. Most 32-V transmitters do require a bit of work on the "band-in-use" slide rule dial as the illumination (using the ten #328 lamps) is problematic. Also, usually the white plastic backing of the slide rule dial needs to be replaced for first-class appearance. A built-in sidetone oscillator is provided in the CW mode and a PTT function is included for AM. The transmitter is stoutly built and weighs in at over 100 lbs. The PA tube is a Raytheon 4D32 with selectable plate voltage - either 600 or 700vdc -  the lower voltage allowing the 4D32 to run at the manufacturer's specifications for continuous duty. The modulator tubes are 807s. The power output is generally around 100 watts. If the 32V-2 is conservatively operated, it is virtually indestructible. A really fine transmitter that is easy to use, reliable, ample power capabilities and allows high quality audio in the AM mode and a very stable CW mode. The 32V-2 was replaced by the 32V-3 in 1952.

National Company, Inc.  - HRO-60R

Introduced in 1952, the HRO-60 was the last of the evolution of tube-type HRO receivers from National. The power supply is built-in but, to the last, National retained plug-in coil assemblies and the famous micrometer dial (it wouldn't have been an HRO otherwise.) The HRO-60 is double conversion above 7MC, has two RF amplifiers, three IF amplifiers and P/P audio output using 6V6s - 18 tubes in all. The selling price was high at $480 but by production's end, in the early sixties, the price had escalated to nearly $750! Coil assemblies were available for frequency coverage from 50-430KC, 480KC-35MC and 50-54MC. The linear dial uses removable plastic scales that are mounted to a rotatable drum for single band-in-use readout. Two accessory sockets are provided for the optional NBFM adaptor and optional 100KC-1MC Crystal Calibrator. Shown in the photo is the unusual HRO-60R, a rack mount version that included the MRR-2 table rack and the SC-2 speaker panel featuring storage for extra coil assemblies behind the doors.

Some Ham AM ops consider the HRO-60 receivers inferior in performance when compared to the earlier HRO-50 (single conversion, two IF amps) though this opinion is usually based on the audio response which is more restricted on the HRO-60 due to its increased selectivity. The HRO-60 (and the HRO-50-1) used pairs of IF transformers to increase the passband selectivity and added an extra IF stage of amplification compared to the earlier HRO-50. The HRO-60's increased IF selectivity was necessary due to the crowded band conditions of the fifties. Another issue with the HRO-60 is the alignment instructions contained in the National manuals. Many HRO-60s are incorrectly aligned due to the confusion of at least two different first conversion oscillator frequencies used at various times during production. National published at least two different manuals with different first conversion oscillator frequencies, 1990KC and 2010KC. Low-end tracking suffers on coils sets A and B when the incorrect conversion frequency is used. When properly aligned, the HRO-60 has tremendous sensitivity with low noise, impressive selectivity (QRM is rarely a problem) and "respectable" audio from the P/P 6V6s. Due to the lack of a true speaker enclosure, all rack mounted HROs sound a little "thin" when used with the SC-2 type of speaker panel. (If you want a good laugh and happen to have some older issues of Electric Radio magazine, check out the cover of ER issue #27 - July 1991 - for a photo of this HRO-60R shown above along with your's truly, WA7YBS.)

Hammarlund Manufacturing Co., Inc. - HQ-140X

The HQ-140X was the next evolution of the famous and popular HQ-129X. It essentially revamped the circuit to use more modern miniature tubes and to provide a separate LO tube and separate mixer tube rather than the single converter tube used by its two predecessors - the pre-war HQ-120X and the post-war HQ-129X. Eleven tubes are used in the circuit including one RF amplifier, three IF amplifiers and a voltage regulator tube. The high quality audio is from a single stage 6V6 providing just a few watts of power. It was around this time that Hammarlund switched from using tubular capacitors in their circuitry to ceramic disk capacitors and the HQ-140X is one of the first receivers to use almost all ceramic disks making major cap replacement unnecessary today. Of course, there are still the electrolytic capacitors and three paper tubular caps to deal with. The brown knobs of the earlier HQ-140X gave the receiver a unique look that must not have been very popular as later models sported dark gray-black versions of the knobs. The HQ-140X sold for around $250 and was offered from 1953 up to 1955 when its successor, the HQ-140XA, came on the scene for another few years. 

National Company, Inc. - NC-98

National upgraded their introductory ham receiver, the NC-88, by adding an S-meter and a two-step crystal filter. This receiver was dubbed the NC-98 and the selling price was increased about $30 over the NC-88 - to about $150. The receiver was a continuation of basic receiver designs for beginning hams that gave good performance with most of the ham necessities and styling that was impressive enough. The NC-98 uses one RF amplifier and two IF amplifiers in a nine tube circuit mounted on a copper plated chassis. Frequency coverage in four bands was from .54 to 40MC and the bandspread was calibrated for the ham bands along with a logging scale. There was an "SW" version that had the bandspread calibrated for the major shortwave bands instead. A separate speaker was required. These introductory-type ham receivers give good performance considering the circuit limitations. The NC-98 was offered in 1954 and 1955.

E. F. Johnson Company - Viking Navigator

The E. F. Johnson Company has been in business since the 1920s and is still active in the component business. During the post-WWII period up to about 1974, Johnson was a major builder of ham transmitters, ham accessories and other communications equipment. The Viking Navigator was introduced in 1957 and was available for about four years. It could be purchased as either a kit or fully assembled. The transmitter-exciter is only 40 watts input power with a little over 25 watts of output power on CW only. Coverage is 160 meters through 10 meters. The PA tube is a 6146 with about 400vdc on the plate. The Navigator featured a fairly standard Johnson VFO, although regulation is somewhat different than their standard VFO as found on the Ranger, for example. Also, a keyer tube is used which provides adjustability of the CW keyed waveform shape. The "Iron Vane" meter is a source of many problems and its accuracy is always in question. The slide switch that selects Grid or Plate current is also somewhat problematic. Many times, Navigators are found with these two parts replaced. A great QRP CW transmitter that is very small and light weight. Original selling price was $199.50 wired and $149.50 as a kit. Only 840 Navigator transmitters were produced. The Navigator shown was donated to the museum by K6QY.

When operating a Navigator as a CW QRP transmitter, the "Iron Vane" meter is constantly "banging" against the zero-stop. Sooner or later, this must have resulted in the meter needle breaking off and ruining the meter. That's probably why nowadays so many Navigators have replacement meters. It's very easy to install a jumper across an original meter's terminals to protect the meter and then use an external watt meter to load up the transmitter. A defective original Navigator meter will be next to impossible to replace so this easy protection assures a functional original meter will survive indefinitely.

E. F. Johnson Company -  Viking Desk Kilowatt, Viking Ranger, Viking KW Match Box

The Viking Desk KW was introduced in 1955 and was available up to around 1964. The "Desk" is a high power RF amplifier with a high power audio modulator, power supplies and all of the control equipment built into a fairly compact "pedestal." The Desk KW features continuous tuning from 3.5 to 30mc. The PA operates Class C and has two output levels, low power for tuning up or operation at 250 watts carrier output or high power for 1KW input power. Plate voltage is either 1300vdc or 2600vdc depending on the output power selection. An external  bias supply can be inserted into the Desk KW for linear operation for SSB. The PA requires 30 watts of drive for full output and the modulator requires 15W for full audio drive on AM. The PA tubes are a pair of 4-250A tubes (4-400 on later Desks) modulated by a pair of 810 tubes. The entire unit is on guides and rollers and is easily accessed for testing or adjustments. The desk itself was a $123.50 option that could be bolted to the side of the pedestal for complete operating station desk with room for the exciter and the station receiver. The Desk KW sold $1595 without the desk. The Desk KW shown is number 280 of the 402 built.

The Viking Ranger was a 75 watt CW or 65 watt AM exciter-transmitter that covered 160M to 10M and had a built-in VFO that was very stable. The audio section featured a special modulation transformer with a winding that was used for negative feedback resulting in excellent quality audio. The PA tube is a single 6146 and the modulator tubes are a pair of 1614 tubes. The Ranger had all of the outputs accessible to interface with the Desk KW for sufficient drive for full output from the Desk KW. Rangers were very popular as a stand-alone transmitter also, especially for Novices since the power limit then was 75W on CW only, crystal control (you got to use the VFO after you up-graded your license.) Still today, the Ranger is a popular transmitter for vintage AM because of its excellent audio and "bullet-proof" construction. Over 14,000 Rangers were built. They were available as either a kit or fully assembled. Prices were $293 assembled or $214.50 as a kit. The later version was designated as the Ranger II and featured different modulator tubes, a two-tone gray paint job and dropping the 11M coverage in favor of 6M coverage.

The Viking Match Box was a heavy duty, balanced antenna coupler that was link coupled, used bandswitching and had two split-stator variable capacitors that allowed matching various kinds of antenna loads to a transmitter. The Match Box was specifically designed for balanced antennas but could also match coax fed loads or end fed wires. The SWR bridge required an external Directional Coupler to function but the Match Box was available without the SWR bridge option in which case there is no meter installed. A built-in antenna relay is included inside the box with access via an external terminal strip mounted on the rear of the unit.

The Viking Desk KW shown was partially disassembled and was going to be "parted out" by the University of Nevada (in 1997.) A friend of mine that worked at UNR saw the Desk KW (disassembled) in the hall on the second floor of the Electronics Building. His phone call to me was something like,... "you interested in a Johnson Desk KW? Well you better get over here, they're throwing one away." When I got to the Electronics Building, I found the Desk KW apart and looking like it was destined for destruction. I asked around and finally found that the Wolf Pack Ham Club had gotten the Desk as a donation and they weren't sure what to do with it since they couldn't move it to the third floor where their ham club station was. I made a deal with them of cash for some equipment they wanted to buy and then the Desk KW was on its way to Virginia City. The KW Matchbox was included in the deal. I rebuilt the Desk KW and it is now fully operational and usually on the air on the Saturday Morning West Coast AM 75M Net. The Viking Ranger was the XYLs Novice transmitter back in 1975. We've always kept it in operational condition. Several years ago I replaced all of the aging capacitors. Other than increasing the wattage rating of the regulator resistor (but not changing its proper location in the VFO) no mods are installed  - Rangers sound very nice with stock audio.

Collins Radio Co.  -  75A-4 

Considered by many radio amateurs to be the finest "ham bands only" tube-type receiver ever produced. The Collins 75A-4 was introduced in 1955 and manufactured up to about 1958 or so, with around 6000 total production. The 22 tube circuit featured a 3.1 kc mechanical filter and a product detector, making the 75A-4 ready for SSB - but it could also copy AM quite well since a separate AM envelope detector was also provided. For better AM copy an optional 6.0 kc mechanical filter could be purchased or, for CW, an 800Hz filter was available. Later, other filter frequencies were offered, e.g., 500 cycle for CW, 2.1 kc for SSB, plus others. Up to three mechanical filters could be installed, providing optimum selectivity for CW, SSB or AM. Frequency readout was "Collins accurate" and sensitivity was competitive. Audio was little better than communications grade. The 4:1 vernier knob was an early option that allowed for very smooth tuning and the later models had it installed "from the factory."  Earlier models had a fairly high hum level and problems with the AVC. Collins installed up-grades rather early in production to correct these problems, although there were many upgrades from Collins through most of the 75A-4 production. Collectors favor the later serial numbers (higher than 4000) since all up-grades were in place by that time. However, Collins offered service bulletins and up-grade kits which many owners installed themselves, so serial numbers alone do not tell you the performance capabilities of a particular 75A-4. Shown above is 75A-4 sn875 (with all up-grades.) I purchased this 75A-4 in April 1970 and it has been "paired" with a matching KWS-1 (sn616) transmitter since December, 1970. For the past 39 years, they have been my regular SSB/CW station.

Collins Radio Co.  -  KWS-1

The KWS-1 was an incredible transmitter when it was introduced in 1955. At a time when AM dominated the voice mode of communications, Collins introduced a high-power SSB transmitter that was so expensive, nobody could afford it - $2100. Everything about the KWS-1 is first-class. The construction was military-grade, the components first-rate and the design was "cutting edge" for 1955. Total production was around 1600.

The KWS-1 is capable of 1KW SSB transmission utilizing a 3.1kc mechanical filter and balanced diode-ring modulator to create the selectable USB or LSB signal with suppressed carrier. Further mixing in various stages coverts the signal to the proper output frequency. It is then routed into the Class AB-1 Linear Amplifier comprised of two 4X150 external anode, air-cooled tubes run in parallel (now 4CX250Bs.) Plate voltage is 2KV. The power output of a properly operating KWS-1 is around 650W DC. In the AM mode, the carrier is re-inserted but the signal is still kept in a single-side band mode. Operating a KWS-1 in the AM mode will usually foment some negative comments from "strict DSB AMers" but, unless mentioned, many never notice that only one sideband is being transmitted. Since AM is a 100% duty-cycle mode, the power has to be reduced to about 400W input. In the CW mode a full 1KW can be utilized since the duty-cycle is usually around 50%. Due to the 3.1kc mechanical filter, the KWS-1 sounds incredible on SSB today since most hams are used to hearing rather narrow SSB (2.1kc) and generally a QSO will garner positive comments on the audio.

The KWS-1 power supply is contained in the larger floor mount pedestal. Originally, a pair of 866A MV tubes were used as rectifiers but most have been replaced with 3B28 HV rectifiers or some even go SS rectifiers (I use 3B28s.) The regulated screen voltage is adjustable and so is the plate voltage to a certain extent (you can move the connections to different taps on the plate transformer.) The squirrel-cage blower is also mounted in the base of the pedestal. It is fairly noisy (bearings should be lubed every few years) and the air output is routed through a 2" diameter radiator hose (for lack of a better description.) The 2KV plate voltage is run through a cable made from RG-58U and the connector on the RF unit is somewhat problematic in its ability to stay connected. The remaining power is routed through a flexible cable with rectangular Amphenol multi-pin connector.

I purchased my KWS-1 SN:616 from its original owner in December, 1970. It has been my main transmitter for many years and has proven to be a super-flexible unit capable of high power SSB and CW with reduced power AM and RTTY communications. The KWS-1 is mostly original with only routine maintenance having been performed over the years. I did have to repair a broken flex connection on one of the roller inductors a few years ago, also a broken wire in the microphone connector. Lately, I've been using the KWS-1/75A-4 on AM on the West Coast Military Radio Collector's Net where it provides a unique type of AM for enthusiasts to hear - one sideband with carrier. The KWS-1/75A-4 have a long association with military MARS stations and, of course, the SSB promotion that involved the Air Force in the mid-fifties. The KWS-1 is certainly one of the best from the "Golden Age of Ham Radio."