Western Historic

RADIO  MUSEUM

~ WWII Communications and Special Receivers ~

~ Post-War Ham Gear and Communications Receivers ~

1942 - 1955

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

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. The RAZ-1 is used with a ten foot in diameter, remotely tuned loop antenna. 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.)

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 CR[N]V-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 (CR[N]D-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 [N] in Navy designation indicates Andrea manufacture and [R] indicates RCA.)

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 regenerative LW receiver and is not shown. 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. 

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.

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 provided by an internal dynamotor. Most versions used eight tubes which had the heaters originally wired in dual-series for 24vdc operation (each of four 6 volt tube heaters in series would operate on 24vdc.) The circuit used two RF amplifiers, a converter stage, three IF amplifiers, a duplex diode/triode provided detection, AVC and BFO functions and a 6K6 provided the audio output. The output impedance was internally selectable at "low Z" which was around 600 Z ohms or "high Z" which was around 8000 Z ohms. 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 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 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. Several different BC-348 versions were built during WWII but generally they can be divided into two groups, early types (B, R, etc.) with grid cap type tubes and late versions (N, Q, etc.) with single-ended tubes. Many different contractors built BC-348s but Wells-Gardner probably built the greatest quantity of receivers and is the most commonly seen version. 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 didn't compromise the receiver's performance. Many other dubious mods were published in various surplus conversion books of the day. Additionally, many hams would drill the case with lots of .25" holes thinking the receiver needed extra cooling. Originally, the BC348 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, the BC-348 doesn'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 is a 1943 Wells-Gardner version BC-348-Q with decal from the San Antonio Air Material Group.

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 below under RAO-3.

Wells-Gardner Co. (National Design)  -  RAO-3 

National began supplying the Navy with their NC-100A direct dial readout, coil catacomb band switching receiver as early as 1938. Designated as RAO, the first versions are similar to the standard NC-100A receivers. When WWII began, the Navy wanted minimal radiation from the receiver's Local Oscillator on the antenna. Beginning with the RAO-2, 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.  A 500 Z ohm audio output transformer was incorporated into the circuit as well. RAO-2 receivers will have an ID from National of NC-120. Like most WWII equipment, not all RAOs were built by National. Wells-Gardner Co. was the second contractor for the RAO series, building the RAO-3,4 & 5. The Wells-Gardner versions were generally intended for shore stations. The circuit uses 11 tubes and tunes AM BC up to 30MC and also features a crystal filter, a tone control and a noise limiter. 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. Shown in the photo is the RAO-3 (115vac only) from 1943. I found this particular RAO-3 receiver abandoned, derelict in a greasy driveway in 1969. I repaired it then and initially used it 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. This very same RAO-3 was featured in an "Antique Radio Classified" magazine article in the late 1980s titled "Rios Radio Revisited" and is also pictured in Raymond Moore's book, "Communications Receivers - 4th Ed." under National RAO.

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 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. When used with a ten foot in diameter remotely tuned loop antenna the RBL-5 is a great performer picking up 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.   

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 stated that enemy DF equipment was sensitive enough to detect LO signals up to 100 miles away. While this all may have been true, any radio receiver used onboard ship has to operate in the presence of the many other receivers, transmitters and radar equipment also in use on the ship. None of the receivers can cause interference with ship equipment and must be able to perform its 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.   

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 more or less standard Hallicrafters' production. Around February 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 a special heavy duty build configuration and this receiver was given the designation of AN/GRR-2. These receivers have a potted power transformer built by General Transformer Company, wax impregnated IF transformers and bandswitches, Korite dipped filter choke and audio output transformer, fungicide coating on the solder joints and special heavy duty nylon insulated stranded hook-up wire in the harnesses. Additionally, the AN/GRR-2 reincorporated the gear-driven bandspread tuning system that had been used in the earliest versions of the SX-28 receiver (the gear drive was replaced with a dial string drive in mid-1941 SX-28 production.) The front panel was copper plated under the dark gray paint and the 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. The dust cover with hinged lid provides ample protection whether the receiver is 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 March 22, 1944 - very early in the SX-28A production.

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, which is 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.

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. Collins Radio Co. was a major supplier of radio equipment during WWII. Collins entered into the communications receiver market after WWII with a receiver design that was entirely permeability tuned. Using a precision Permeability Tuned Oscillator (called a PTO - Type 70E-7) and a multiple crystal controlled oscillator in a double conversion superheterodyne circuit, 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 on 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.

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

Radio Corporation of America  -  AR-88, CR-88, SC-88 

RCA's great receiver creation was the AR-88. Designed in 1941 by Lester Fowler and George Blaker, it was a 14 tube superheterodyne with 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. The receiver pictured is actually one of the last of the '88 versions, the SC-88, (Signal Corps designation R-320/FRC, SN 214), from 1950, which has "band-in-use" masking and the crystal phasing control on the front panel (the AR-88's is internally adjusted.) The AR-88 series receivers use three IF stages that are stagger-tuned (with two under-coupled transformers and two over-coupled transformers) requiring a sweep generator and oscilloscope for proper alignment. There is a procedure to align the IF section using just a VTVM but the results are not as good as the sweep method. 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 auxiliary equipment. The Navy designation for the DR-89 was RDM. The diversity receivers did not have S-meters installed because Output Meters (Diode Load current) for all three receivers were actually installed outboard on the Monitoring Unit of the DR-89/RDM rack. Some AR-88D (table top version) receivers did not have S-meters installed due to a shortage of meters that occurred during WWII, however the wiring for the meter was included in the harness for future installation. The Signal Corps had their versions of the triple diversity DR-89 with military IDs (OA-58A/FRC) and slightly different receivers, i.e., the CR-88 and the SC-88. The AR-88LF and CR-91 were versions with a VLF band in place of the AM-BC band. If you happen to be working on the SC-88 version, be aware that there are several changes in the component designations between it and the AR-88 version. If you don't have the R-320/SC-88 manual, using the AR-88 manual will provide most of the information necessary but front-end alignment components have different locations and different designations. You will have to trace out which coils and trimmers are involved for each band and each function prior to beginning the RF alignment. The SC-88's IF section is very close to the AR-88's except that the crystal filter phasing is a front panel adjustment.  

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. 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 seem to function very well. Dial accuracy and stability - both necessary for RTTY work - was the 51J selling point to the Signal Corps and still today are the 51J's primary attributes.

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. Hammarlund also offered a "JL" version with 100-400KC substituted for the .54-1.35MC band and a "VLF" version that covered 10-540KC. There are also other versions with somewhat different frequency ranges. The last model variation - the SP-600 JX-21A from 1969-1972 - 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 velvet-smooth tuning system that can impart a sensuous pleasure to just searching for stations. 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. The S-meter is not illuminated and a switch is provided to indicate either carrier level or audio output. The SP-600 model numbers usually will have a suffix with J or JX followed by a numeral. 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 frequencies. The user could switch to any of the crystal frequencies for increased stability for that particular frequency. The number following the suffix generally indicates specific features for that version, e.g., contract or end user, tuning range, circuit upgrades, etc., with the number ranges being more or less chronological. 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. All early versions of the SP-600 receivers were built using molded tubular capacitors of various manufacture - Cornell-Dubilier and Sprague are the common types encountered. Nearly all molded capacitors are defective nowadays, requiring extensive replacement work when rebuilding an SP-600. Later versions had more reliable ceramic disk type capacitors installed rather than molded capacitors. 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. This is the early version of the JX-21 so it does not have the product detector SSB changes. 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 are looking for a "to the kilocycle" accurate frequency readout and are willing to sacrifice audio quality,...well, maybe you'd want something by Collins instead.

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 very 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. It 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 - what the 37.4 stencil on the front panel indicates is unknown but it might be a reference to a military RTTY bit rate.

1955 Collins R-390A (built in 1956) 

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. The HRO-60 receivers are sometimes considered inferior in performance to the HRO-50 (single conversion) though this opinion is usually based on the audio response which is more restricted on the HRO-60 due to its increased selectivity. Additionally, the HRO-60's first conversion oscillator can be substantially mis-aligned and the receiver will still seem to function correctly, receiving stronger signals on the higher bands. Additionally, National published two different first conversion oscillator frequencies, 1990KC and 2010KC, making alignment errors common. When properly aligned, the HRO-60 has tremendous sensitivity with low noise, impressive selectivity and respectable audio from the P/P 6V6s. (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 particular HRO-60R along with your's truly, W7HTR - although I was WA7YBS then.)

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.

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. I have used a 75A-4 (SN 875 but with all up-grades) with a matching KWS-1 (SN 616) transmitter for the past 37 years as my regular SSB/CW station. The 75A-4 (SN 4470) shown was built in 1957. See our "RTTY-With Real Machines" webpage for more details on our KWS-1 and 75A-4 combo, navigation link at the bottom of this page.

Amateur Radio Station W7HTR - Vintage AM Station

This is the operating position of our Vintage AM Station. We are usually found on 3870kc on Saturday mornings 7:30AM to 9:00AM PS/DT participating in the Saturday Morning West Coast "Earlybird" Net. The station has the following equipment:

E. F. Johnson-Viking Desk KW, Viking Ranger, KW Matchbox ... This Johnson Desk KW was originally a donation to the University of Nevada's "Wolf Pack" Radio Club. The club was considering "parting out" the rig since they couldn't move it to the third floor of the Electronics Building where the club's radio station was located. It was partially disassembled on the second floor when an employee of the university (and a fellow ham) spotted it and gave me a call. Something like ",...are you interested in a Johnson KW amplifier?"  Followed by ",...well, you better come over here quick because I think they're going to throw it away." The Desk KW was in pieces on the second floor of the Electronics Building and looked like it was destined for destruction. It turned out that although the club was considering parting out the Desk KW, they didn't know exactly what would persuade them to put aside that destructive plan and accept a suitable trade instead. We finally agreed on a trade of cash to buy some equipment the club wanted. The KW Matchbox was "thrown in" for an extra $50 - the total price was $250. I brought home the main parts of the rig and found that a few parts and minor trim pieces were missing. Another trip to the University found all of the missing parts upstairs in one of the storage areas for the club radio station. I reassembled and rebuilt the Johnson Desk KW, finding that there were a few minor mods to allow the rig to be used as a linear amplifier with a Hallicrafters HT-37 as the exciter but it was an easy task to return everything to original. There were a few broken wires in the main harness and all of the relays needed a thorough cleaning. We have owned this Desk KW for around 10 years now. The Viking Ranger is the XYL's original novice transmitter from 1975. I rebuilt it about 15 years ago and it has always been a reliable, "bullet-proof" little rig. No fancy audio mods - just the stock circuit receives great audio reports. I drive the Desk KW direct with the Ranger with the Ranger's drive control adjusting the input current to the Desk. Although I have run the Desk KW at full power into a dummy load, when it is "on the air" it is running in the low power mode - about 250 watts of carrier output. This Desk KW is #280 of the 402 built.

Collins 32V-2 ... I've owned the 32V/75A combo for around 12 years. The 32V-2 is in very nice cosmetic condition and didn't require too much work to have it functioning like new. I had to replace a shorted fixed-value capacitor in the pi network and another capacitor in the mixer section of the transmitter. I also replaced the intermittent auxiliary relay with a good condition used original part. I also had to rebuild the slide-rule dial. These dials usually show their age because of discoloration of the white plastic backing located behind the plexiglass square rods that make up the "band-in-use" lighting system. Once a new white plastic sheet is in place and the square rods clean, the dial looks like new and the illumination is nice and bright. Another problem is the plastic used for the kilocycle dial. These dials frequently will turn brown or red with exposure to intense sunlight. This 32V-2 was no exception and a repro dial had to be installed. The transmitter runs a single 4D32 modulated by a pair of 807s for about 110 watts of carrier output power. An excellent performer with Collins' accurate dial readout, first class audio and sufficient power to usually receive good reports.

Receivers ... Collins R-390, Hammarlund SP-600 JX-21, Collins 75A-1 are all covered above on this webpage. The Hallicrafters DD-1 is covered in the "Pre-WWII Ham Gear" webpage or the "Hallicrafters DD-1 Restoration" webpage.