Radio Boulevard
Western Historic Radio Museum

WHRM Radio Photo Gallery

(Airport, Shipboard, General Purpose & Military Gear)

PART 1 - 1932 - 1942 & 1946 - 1950

PART 2 - 1950 to 1969

(For WWII gear go to "WWII Communications Equipment"  -  Nav Link in Index Below)


photo: Radio Room of the USCG Cutter Taney ca: 1940

Commercial & Military Communications Gear - 1932-1942 & 1946-1950 - PART 1

Pre-WWII Gear - 1932 - 1942


Airport Communication Receivers

National Company, Inc. - 1932 to 1934 Airport Receivers 

By the early thirties, National had grown from a company that produced radio parts and regenerative TRF receivers into one of the top shortwave receiver producers in the country. National's chief engineer and general manager, James Millen, had guided the company from its early radio designs (that usually had National as a parts supplier) into the new shortwave receiver market that was becoming popular by 1930.

In late-1931, National Company was selected by the Department of Commerce (who was in charge of airports and airways through the Aeronautical Branch) to build new superheterodyne receivers to replace the old regenerative receivers then being used at airports around the country. The entire system upgrade of airport and airway communication equipment included General Electric, who got the contract for the new transmitters and Aircraft Radio Corporation, who got the contract for the  new airborne gear. National got the contract for the ground-based airport receivers. It seems likely that Herbert Hoover Jr. and his West Coast design team were involved in some of the electronic engineering work of the new receiver that was designated RHM. The contact was identified as 32-15305 and was dated May 12, 1932. The RHM was National's first superhet and it had some of the features that were to become National's trade-mark. Plug-in coils to select the tuning ranges, a separate power supply and a micrometer-type tuning dial are foremost in the design and were to become standard features for National receivers over the next several years.

Since the RHM was a commercial airport receiver it had to be built with the best material and best parts available to assure top reliability and performance. Each receiver was hand tested and aligned by engineers at National resulting in a very modern receiver that provided excellent sensitivity and selectivity (along with top-notch image rejection due to its TRF amplifier stage. Frequency coverage of the RHM was 2.3mc up to 15.0mc using a set of 15 coils. Each band required three coils, RF Amp, Mixer and Local Oscillator which gave the user five tuning ranges. The IF was shown as 600kc in the operating instructions but it seems likely the 500kc was the actual IF.*. It's likely that only around 100 RHM receivers were built and just a few survive today since most of the airport equipment was scrapped when it became obsolete.

The AGS-X "Single Signal" Receiver - To take advantage of the prestige the Department of Commerce contract had given them (and to profit through additional sales to the general public,) National adapted the RHM for commercial and ham use dubbing it the AGS. National's advertising implies that AGS receivers continued to be provided for airport use after the initial RHM contract. These receivers had many upgrades from the earlier RHM with more frequency coverage with better calibration procedures and some later-style tubes.

The major AGS-upgrade was with the introduction of the "Single Signal" AGS-X in March, 1933. The AGS-X was tailored for ham needs in that a front panel BFO control and a James Lamb crystal filter were added to the receiver. In late-1934, optional 10 meter coils were added as the AGS frequency coverage was increased to reflect the needs of a "ham receiver" (although at $265 with all accessories, not many hams could afford it.) The AGS-X shown in the photo to the right is serial number F-151 dating from 1934. This particular receiver was originally purchased with all 27 coils that were available at the time. That would have been the standard general coverage coils for the five tuning ranges from 1.5mc up to 20mc, totaling fifteen coils. Also, the amateur bandspread coils that covered 160M, 80M, 40M and 20M (12 coils.) Each ham band was tuned within 100 divisions of the the Type-N micrometer dial (20 to 120 on the scale that was 0 to 150 divisions in a 270º rotation.) Two coil holder rack panels were necessary to store all of the coils which would be 12 coils in each rack and 3 in the receiver. These rack mount coil holders differ from the earlier RHM coil holder that was a combination of a wooden holder with a metal front panel in that these later coil holders are a metal panel with four flat spring retainers per coil. The power supply is the GRSPU for powering a single AGS receiver. I built the table rack that this AGS-X is mounted in based on a ham station photograph that appeared in a 1934 QST magazine. The rack is built from 3/4" square steel tubing with welded joint seams.

Although the initial high selling price may have limited the sales of the AGS and AGS-X receivers to the ham market, as the receiver design began to show its age the prices dropped significantly. By 1935, Leeds was selling the AGS-X for $123. Since National had introduced the HRO by that time, the AGS was considered obsolete technology and priced accordingly.

Other RHM/AGS Family Receivers - In addition to the RHM and AGS receivers, National also produced the RHP and RHQ receivers that were very similar to the RHM within their design circuitry but ganged the three coils together behind a small panel that created a plug-in "coil set" for each tuning range covered. Additionally, the National Type-N micrometer dial was replaced with a National Type-BX illuminated "Velvet Vernier" dial similar to those used on the SW-3 receiver. The RHQ receivers were specifically designed for airport communication and therefore were only supplied with two coil sets that allowed tuning from 2500kc up to 6500kc. The RHQ was also identified as the AGU receiver in some uses (photo below.) Also, National produced a long wave receiver built along the same lines as these early airport receivers, the RIO (see below.) The RIO was also produced as the RIP and was also identified as the AGL. There was a slight difference in the RIP/AGL frequency coverage in that the RIO tunes 175kc to 650kc while the RIP/AGL tunes 175kc to 750kc.

photo above: AGS-X SN: F-151


The RIO Receiver - Many of the navigational and communications requirements for some airports and various airways stations were not on HF but were on lower frequencies. In 1933, National supplied the RIO receiver for tuning those lower frequencies, 650kc down to 175kc. The circuit is not a superhet. The RIO uses three TRF amplifiers followed by a detector and audio output stage. Additionally, an AVC circuit and a "tracking" BFO circuit are provided. Use of a TRF circuit was to allow complete tuning within the 400kc region of the spectrum. Any of the common IFs used at the time would have interrupted the tuning coverage somewhere within the tuning ranges provided. Also, at the lower frequencies, noise was always a problem and the TRF circuitry was considered to be one of the "quietest" tuners. Seven tubes are used. The RIO is powered by the same type of power supplies as the AGS used. The dial should be a National BX although the dial on the the receiver above appears to be a replacement from an SW-3 receiver. This particular RIO shown above is serial number 3. It's functional and is a very sensitive low frequency receiver.

photo left: The AGS Airport or Airway station setup (bottom to top) dual power supply GRDPU-26, 58C monitor receiver, AGS receiver, spare coil holder and loud speaker. Note that the AGS receiver has the short data plate indicating it's an AGS (the RHM used a long data plate.)
Photo from:  Radio News - January 1933

The RHQ Receiver - Shown to the right is a B&W of the RHQ receiver I owned back in 1990. I had both coil sets plus one spare. The receiver did function on all original parts. This photo is from the article I wrote for Electric Radio (issue #27) on the AGS Receiver in 1991. Unfortunately, I sold the RHQ around 2005. It's possible that since this receiver was missing its ID plate that it could have been either the AGU version or the RHP. All three versions are very similar in external appearances.

RHM in Top Photo - I've owned this particular RHM receiver since early 1991. It came with all fifteen original coils and the original wood and metal, rack mount spare coil holder. This receiver was missing its original ID plate but the dust cover was marked "RHM #4" in black grease pencil. The ID plate shown in the photo is a reproduction (not a very good one.) This RHM is functional on "all original parts." This only means that the receiver barely functions. It does receive stations and it seems to work okay. However, I recently obtained RHM SN: 8. This receiver was rebuilt (by me in the late-1990s) for NU6AM whom I purchased it from in May 2018. This RHM is a phenomenal performer with excellent sensitivity and stability. This shows that, when new, the RHM receivers could certainly have met the demands of airport and airway communications service. Today however, the performance of any of the RHM/AGS family of receivers, even rebuilt ones, will seem somewhat antiquated and crude. In 1932 they were "state-of -the-art" but, within just a few years, National had completely surpassed these receivers in design and performance with their HRO receiver.  >>>
>>>  Although the RHM/AGS performance might be considered "dated," the fact that many of these receivers are still operational and are still fairly accurate in their dial readout is testament to National's build quality and Herbert Hoover Jr. and James Millen's design capabilities. This same design team again worked together in 1934, producing the famous HRO receiver.

* 600kc IF for the RHM? - I've seen two manuals for the RHM. The first one I owned had 500kc IF penciled in. The second manual didn't have the correction and shows that the RHM manual has a significant error in that it has the IF at 600kc. I tried aligning the RHM to 600kc and the results made it obvious that 500kc is the correct IF. The first manual was "hand corrected" but the second manual never was. Interesting.


RCA Manufacturing Company, Inc.  -  AVR-11A Airport Receiver

RCA supplied some airports with this 16 tube superheterodyne receiver beginning around 1937. The receiver used many of RCA's developments, including the "Magic Brain" which was a modular receiver "front end" and the innovative "band-in-use" dial mask. Many other components are recognizable as exclusive-RCA parts and included the "Magic Eye" cathode ray tuning indicator. RCA included a BFO, a sensitivity control, a noise suppressor circuit and a headset output jack - all necessities for a communication receiver. Additionally, an optional Crystal Filter assembly was available on special order. There were three models available, the AVR-11 that was installed in a metal cabinet with matching speaker. The AVR-11A was a rack mount receiver with gray painted panel but without a chassis dust cover and with matching rack mount speaker. The AVR-11B was a rack mount with dust cover with black painted panel and rack mount speaker. 

The AVR-11 receivers provided frequency coverage from 140kc up to 23mc which was more or less standard for the largest "All-wave" receivers. The airports favored the longer wavelengths used in air navigation, weather reports and for some airport communications in the 1930s. Higher frequencies were also starting to be used at the time, so the coverage up to 23mc was also an advantage. The dial also provided a logging scale for an accurate frequency reset function. The "RCA Magic Eye" (RCA's 1936 selling moniker for their cathode ray tuning indicator) was installed and is on the left side of the panel. The "eye" on the right side of the panel is a "Stand-By" indicator that glows green (looking similar to the actual "eye tube") when the receiver is in stand-by. The speaker system is fairly elaborate with connections for the speaker field coil to double as a power supply filter choke, connections for a "hum bucking coil"  besides the regular push-pull audio output transformer. RCA also offered a 15 tube ham version of this receiver in the ACR-111. RCA Manufacturing Company, Inc. was a division of RCA that built communication and broadcast equipment.

The AVR-11A shown in the photo above is awaiting restoration. I've had it for several years but have yet to get started on the work. The plastic dial cover is missing from the bezel. Much of the front end wiring used rubber insulated wire which has hardened over the years and is now falling off. Very few AVR-11 receivers were produced and they are quite rare in any condition.

To show what the AVR-11 should look like (although the side panels that cover the rack screws are missing,) see the photograph to the left which is the complete AVR-11 owned by Joe Connor, who has supplied this photo. Note that the speaker panel includes a fabulous deco "winged" RCA emblem.


National RCE, ca: 1937

National Co., Inc. - Airport and Airway Communication Receivers

National Co., Inc. had been supplying receivers for airport and airway communications since the RHM receiver in 1932. The mid-thirties HRO also was used in some airports. The most popular airport receiver by far was National's Airport and Airway Communication Receivers that were based on their NC-100 receiver. The continuing upgrading of communication and navigation equipment was initially the responsibility of the Department of Commerce and the Bureau of Air Commerce with its various branches in charge of airports and navigation. The new and developing radio navigation systems provided a pilot the means to fly an airplane to an airport using a radio range beacon called a "beam." The navigational radio beam allowed that pilot to follow a predetermined altitude and route called an "Airway." The navigational beam and various beacon stations also provided two-way communications with pilots to report weather conditions and other information that might be needed by pilots. National's history of providing top quality receivers for airport use (RHM, the fore-runner to the AGS, and the HRO) practically assured them of continuing contracts for airport-specific receivers. The first "moving coil" receivers supplied to airports were standard NC-100X receivers. Some of these early receiver used the "art deco" overlay panel while others used a black wrinkle finish rack mount panel. In 1937, National began supplying the Department of Commerce, Bureau of Air Commerce, Dept. of Navigation (still in charge of airport communications at that time) with the RCD receiver, a slightly modified NC-100X receiver that had the AM BC coils replaced with 200kc to 400kc coils. At the end of 1937, the RCE was introduced and it became the "standard" Airport-Airway Communication receiver from National. When the U.S. Civil Aeronautics Authority (CAA) was created in 1938, National then supplied the CAA with airport receivers. These new CAA receivers were continually being upgraded as new contracts were issued. Some receivers were even produced during WWII for use at both military and civilian airports. The RCK tuned 200kc to 800kc in the two lowest frequency bands and 2.5mc to 23.5mc in the three highest frequency bands. The RCK was supplied to the U.S. Navy during WWII. Also during WWII, the RCL was introduced and it featured a two position bandwidth switch. After WWII, early versions of these receivers (RCK and RCL receivers) were upgraded in the last versions, the RCP and the RCQ. Most of the upgrades were professionally installed by well-known companies such as Schutigg & Company or National Electrical Machine Shops (NEMS.) Even National managed to upgrade a few of their earlier models. These later versions were used up into the early fifties when more modern equipment was becoming a necessity.

Although the Airport-Airway Communication Receivers are based on the NC-100 chassis, there are some significant additions to the circuit. The most obvious is that the receiver is rack mounted and has a very different front panel when compared to the striking "art deco" panel of the standard NC-100 receiver. These receivers use a 3/16" thick aluminum front panel that is black wrinkle finished. All early Airport-Airway receivers were equipped with an I.N.S. control. I.N.S stood for "Interchannel Noise Suppressor," which was actually a "squelch" control. 

Later versions have a C.O.N.S. (Carrier Operated Noise Suppression) control that uses a relay to mute the receiver if no carrier is being received. Additionally, the push-pull audio was changed to single-ended and the output transformer was internal to the receiver. The audio output impedance was 600 Z ohms and 20K Z ohms. Another addition was a relay that could remotely quite the speaker without affecting headset reception. Most Airport-Airway Communication Receivers came with two speakers, a single table top speaker box and a rack mount dual speaker. No carrier level device (meter or eye-tube) was used on the majority of the receivers. The chassis is covered top and bottom with a "slide on" dust cover although early versions have separate top and bottom covers. 12 tubes are usually used in the circuit which utilizes a 457kc IF. Post-WWII receivers RCP and RCQ will have a selectable crystal-controlled fixed-frequency function installed operated by a front panel toggle switch. Shown in the photo left is a 1940 Airway Communication Receiver Type RCF-2 sn:13. The RCF-2 is the only version that is specifically identified as an "Airway Communications Receiver." All others are "Communication Receivers." The Airport Communication Receiver shown in the top photo is a 1937 RCE sn:302 which happens to still have its original dust cover.

Shipboard Radio Equipment

U.S. Navy  -  RAD-2 (CNA-46013)
Contractor: National Company, Inc.

In 1932, the U.S. Navy contracted with National Co. to provide the RAD receiver. The RAD was based on National Company's SW-5 "Thrill Box" but was provided to the Navy with a "complete" set of coils to cover 250kc up to 33mc for the frequency coverage. The coil sets were contained in a box and were assigned a USN model number (CNA-47040) The separate power supply was also part of the RAD equipment supplied (CNA-20002.) The RAD receiver appears to be a stock SW-5 with the exception that it was painted black wrinkle finish and had a large data plate installed on the top lid. Also, each control had an index plate mounted behind the knob.

Shown in the photos is a RAD-2 receiver. The USN model number is CNA 46013. The "project date" is 1932 and the contract is also dated 1932. The photos show that the RAD-2 is almost identical to the standard National SW-5 with the exception of the black wrinkle paint and the index plates behind the two control knobs. Internally, the RAD-2 is identical to the SW-5 except for the black paint. The RAD-2 shown is serial number 13. The screen grid tubes are 24-As and the audio tubes are 27s. Knobs are probably not original.

photos from: WA6OPE


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 in Virginia City, Nevada. John Mackay initially made his fortune in Comstock silver but he later (1883) moved into telegraphic communications. Mackay, along with newspaper publisher James 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 (International Telephone and Telegraph Corp.) 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 Telephone and Radio 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 installed in four pin tube sockets. 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 an "uncalibrated" 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 transmitter's signal could be received as a heterodyne beating with the internal oscillator heard on 'phones plugged into the phone jack. Since the dial is uncalibrated except for a general logging scale, frequency would have been determined using a true frequency meter. Most shipboard transmitters in the thirties operated CW or MCW, so the operator could monitor the transmitted signal for other characteristics or suspected problems (such as drift or other instability,) hence the term "Frequency Monitor." 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 if the receiver was operational. Actual receiver frequency would have to be determined with a frequency meter. The Type 102-B tunes 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.


CGR-32-1 - Coast Guard AR-60 - 1939

RCA Manufacturing Company, Inc. - CGR-32-1 Coast Guard Receiver (AR-60R)

In 1935, RCA offered what must have seemed like the ultimate receiver. So over-built and so expensive that it was obviously not for any Depression-era ham. The AR-60 was priced at an astounding $495 at a time when this amount of cash could easily buy a new car. To those familiar with RCA's equipment built for the U.S. Navy where cost was not even considered as a "limiting factor" the AR-60 was normal "Navy shipboard construction" but the AR-60 wasn't built for the Navy. Though RCA's intended market was the commercial and military users, RCA did advertise the AR-60 in QST one time. RCA obviously didn't expect many sales to hams since the AR-60 was only available through RCA dealers (rather than discount dealers like Leeds and others.) The AR-60 was intended as a robustly-built, extremely reliable, commercial-military receiver that featured performance that was at the limits of the designs of the time. It was a receiver that could endure and survive the rigors of shipboard use and function superbly while doing so. RCA built the AR-60 through their subsidiary, RCA Manufacturing Company, Inc., the division that generally handled all of the commercial manufacturing. RCA also advertised the AR-60 in their Broadcast Equipment catalog. Since the AR-60 was a "limited production" and was a "built-to-order" receiver, the total quantity of AR-60s built from 1935 until 1940 was around 300. Most of these went to the U.S. Coast Guard, one of the major users of the AR-60 (USCG designation CGR-32-1 and CGR-32-2) along with the Signal Corps, where they were used in Triple Diversity receivers. RCA used the AR-60 in some of their Coastal Stations and Pan-American Airlines used the AR-60 in their HF direction finders in the Pacific.

The AR-60 was built on a heavy-duty nickel-plated brass chassis with three nickel-plated brass bottom covers, unheard of, in 1935, for civilian equipment (but a construction method RCA used to reduce corrosion in shipboard equipment.) The receiver tuned from 1.5mc up to 25mc in six tuning ranges. The bandspread range gave great vernier effect because its span was limited to an average of about 100kc for the entire bandspread range (although its exact span depends on the tuning range selected and where you are tuned with the main dial in that range.) The AR-60 front-end used double pre-selection or two TRF amplifier stages, although the double pre-selection is only used on the top three frequency ranges (5.6mc to 25mc.) Radio engineers generally believed that double preselection was only for image rejection and not really necessary below around 7 mc where the receiver circuitry was more efficient. The AR-60 receiver featured an elaborate antenna input system with selectable links for doublets or end-fed wire antennas and then variable antenna primary coupling allowed the operator to adjust how much signal level was going to be needed for low-noise reception. All of the RF and IF coils were wound on ceramic forms. When the three bottom covers are installed the chassis is compartmentalized and fully shielded. Nearly all of the tube sockets are Isolantite (ceramic.) Ten tubes (along with a 991 neon bulb voltage regulator) are used in the circuit and a heavy-duty sectional bandswitch was used. The audio output is from a single 41 tube that uses a 600 Z ohm output transformer. The B+ levels are fairly low in the AR-60 so only about 1/2 watt of audio power is available and since the receiver was designed for commercial use, headsets were the intended audio  reproducers. The AR-60 can be operated on batteries although it requires moving some wires on the terminal boards in the power supply section. The AR-60 was available as a black finished table model (suffix T), as a rack mounted unit with full dust cover (suffix R) or in a deluxe two-tone gray table cabinet (suffix S.)

 Perhaps the most famous use of the AR-60 receiver is aboard the USCG Cutter ITASCA in its assistance to Amelia Earhart's ill-fated flight in July 1937. The ITASCA was equipped with two CGR-32-1 receivers. During the late thirties, many USCG Cutters were equipped with CGR-32-1 versions of the AR-60-R that were specifically built for the Coast Guard. In Nov.1939, a contact was issued for approximately 30 CGR-32-1 receivers for U.S. Coast Guard installation on the ten Lake Class Cutters that were being rebuilt and refitted at the time. This was probably the last contract for the CGR-32-1 receivers. Soon after that, the ten Lake Class Cutters were loaned to England as part of Lend-Lease for the duration of WWII. However, according to the USCG website much of the sensitive equipment was removed prior to delivery of the Cutters. It's likely that the CGR-32-1 receivers were used elsewhere during WWII, either in other USCG facilities or other military uses.

photo left: Radio Room on the USCG Cutter TANEY ca: 1938 showing the two CGR-32-1 (or CGR-32-2) receivers. USCGC TANEY was a Treasury Class Cutter with a spacious radio room when compared to the cramped quarters of a Lake Class Cutter's radio room.                            photo from:

The AR-60-R shown in the top photo is the 1939 Coast Guard version, the CGR-32-1 bearing the serial number of 25. This receiver was built on contract Tcg-31919, dated November 16, 1939, which was probably the last contract for CGR-32-1 receivers. This CGR-32-1 is a functional example and its performance is impressive. Very similar to the Hammarlund Super-Pro SP-100 in overall front end noise and sensitivity. Very similar to the 1940 Navy RBB and RBC in audio output capabilities. Coupling and Antenna Trim controls will interact somewhat but it's best to set the Coupling to the minimum amount that gives the desired signal level. Although maximum Coupling will appear to result in stronger signals it will also produce higher noise levels that will interfere with signal copy. The two 0-100 dials necessitate using a frequency meter or signal generator as a calibrated signal source unless you have the frequency chart from the manual. Weighing in at 75 lbs, the AR-60 is a durable, robustly-built, almost indestructible receiver that can still perform in an impressive manner.

The AR-60 was available from RCA Manufacturing Company, Inc. (subsidiary of Radio Corporation of America) up until around 1940. RCA was designing the AR-60's successor, the AR-88, in 1940 and that receiver continued the line of robustly-built, durable, hard-working and reliable receivers. More on the AR-88 below,...

For the ultimate information source on the AR-60 receiver, including history, performance comparisons, restoration information, serial number analysis and more, including the frequency to dial readout chart, go to our web-article "RCA's Legendary AR-60 Receiver." Link below in the Navigation Index.


General Purpose Communication Receivers

photo above: SP-100LX sn: 2730 from 1938

Hammarlund Mfg. Co., Inc.

100 Series Super-Pro  SP-100LX

Hammarlund's relationship with the U.S. Army Signal Corps dates back to the Army purchases of a few Comet Pro receivers in the early thirties. The first official Super-Pro contract that Hammarlund had with the Signal Corps was from June 1935 for the SPA receiver. The SPA was, without a doubt, the first version of the SP-10 Super-Pro that was produced. The official Super-Pro announcement for the civilian market came nine months later, in March 1936, with a two-page advertisement in that month's QST magazine. The SP-10 was only produced for nine months before it was replaced with the updated 100 Series Super-Pro receiver.

With the 100 Series, Hammarlund began to offer other frequency coverage options. The standard coverage was .54mc to 20mc but also offered was the SP-100SX tuning from 1.25mc to 40mc and the SP-100LX tuning 100kc to 400kc and 2.5mc to 20mc. The "SX" was considered the ham version since it included 160M to 10M coverage. The "LX" was considered the military/commercial version because of its LF and MW coverage. Certainly the 100kc to 400kc range appealed to Signal Corps users. However, it seemed to limit the "LX" uses for the U.S. Navy and for most commercial shipboard use since the maritime 400kc to 500kc band wasn't included in the tuning range.

Most SP-100LX receivers went to the Signal Corps although there certainly were some commercial users also. The entire frequency coverage appealed to airport radio operations since LF-MW Navigation could be tuned in. Also, the aviation uses in the 2mc to 3mc range were mostly available and the popular airport communication uses in the 6mc part of the spectrum could be utilized. Whether many airports wanted to spend the $450 list price for the Super-Pro would have been a consideration however. Certainly, Army aviation use must have been popular since most of the LX receivers that turn up today seem to have Signal Corps stamps on them. Additionally, the 100 Series Super-Pro's successor, the SP-200LX was also a very popular Signal Corps receiver. 


RCA AR-88D ca.1944

Radio Corporation of America  -  AR-88 Series

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

RCA's most successful communications receiver was the AR-88. Designed in 1940-41 by Lester Fowler and George Blaker (and rushed into production because of WWII requirements) the AR-88 was a 14 tube superheterodyne that covered .54 to 32MC in six tuning ranges and featured incredible sensitivity (even up to 10 meters), excellent stability and high fidelity audio (from a single 6K6.) Most of the production was sent to England, Russia or other Allies during WWII because of Lend-Lease which accounts for the relative scarcity of the early versions of the receiver in the USA. The AR-88 was used extensively in Great Britain during WWII for various purposes. RCA and Radio Marine Corp.of America also used the AR-88 and its variants in their own installations for various purposes. Even the US Military used some of the later AR-88 variations in their installations. Contrary to some published estimates of unbelievably high production levels in excess of 100,000 units, serial number analysis seems to indicate that around 30,000 AR-88 series receivers were built between 1941 and 1953.

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

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

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


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

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

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

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

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

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

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

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

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


Post-WWII Gear - 1946 - 1969


Airport Communication Receivers

National Company, Inc.  - RCR Airport Receiver

National had been supplying "Moving Coil" receivers to airports since 1937. All of those receivers were based on the NC-100 receiver with some special modifications for airport communications. After WWII ended, National upgraded many of their earlier Airport Receivers generally designating them as either RCP or RCQ receivers. In 1947 or '48, National was given a contract for an Airport Receiver that would be based on their then current production commercial communication receiver, the NC-240CS. The receiver was designated RCR and it represents the last of the "Moving Coil" receivers that National produced for airport communication use. The RCR was built for contract number Cca 26391.

The RCR is very much a NC-240CS with only a few changes. The NC-240CS dial scale is the most obvious with its light amber color - quite different from the cream color dial of the standard NC-240D. The other change is the data plate that identifies the receiver. The RCR and the NC-240CS provide a 500Z ohm and an 8Z ohm audio output along with an option to allow a 10K Z ohm input the essentially parallels the audio output transformer in the receiver with another audio output transformer mounted on the speaker. This allowed using the regular National table speaker if desired. Also, one could opt for the rack mount version of the speaker. It was also acceptable to just use the 500Z or 8Z ohm outputs for audio output connections. The audio output uses push-pull 6V6 tubes which differs from previous National Airport Receivers that used single audio output tubes. Since the RCR is a commercial receiver it doesn't have amateur bandspread coils and its six bands covers 200kc to 400kc (Band F) and then 1.0mc to 30.0mc (Bands E to A.) The receiver uses 12 tubes and is single preselection with two IF amplifiers and provides a crystal filter for selectivity control. A Noise Limiter and Tone control are also provided. The RCR was rack mounted and features a slide-on dust cover that entirely encloses the receiver chassis. All cables can exit from the sides of the dust cover with only the mounting screws and the removal handles on the back of the dust cover (although there is a square cut out for the power cord to exit directly to the rear if necessary.)

The RCR shown was installed at a CAA facility located in Honduras, Central America. Its serial number is 17.


Shipboard Communication Receivers

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 receiver shown was built in 1952. Mackay receiver serial numbers generally incorporate the last two digits of the year of manufacture as the first two digits of the serial number. 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. 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 types of Mackay receivers date from the late forties and were manufactured through the fifties. (See our "Vintage Longwave Receivers" webpage for an in depth article about this receiver.)


Radiomarine Corporation of America  -  AR-8506-B  aka: R-203/SR

The origins of Radiomarine Corporation of  America date back to the 1920s,...a time when RCA was controlled by General Electric and Westinghouse. When RCA was created in October, 1919, the US Navy wanted a radio company that could handle operation of the coastal wireless stations, service all the equipment, provide sales of new wireless gear. General Electric created RCA out of some of their own assets and, mainly, with the purchase of American Marconi. As radio developed, GE directed what was to become known as the "Radio Group" - a patent-sharing association of five companies that dominated radio in the early twenties. General Electric, Westinghouse, RCA, United Fruit Company and Wireless Specialty Apparatus owned all of the important radio patents. As radio broadcasting became more and more popular, GE and Westinghouse somewhat controlled that end of business while United Fruit Company and Wireless Specialty Apparatus were more involved with the maritime radio business. Eventually, RCA was able to purchase Wireless Specialty Apparatus (around 1925) and this company became Radiomarine Corporation of America. The virtual domination of radio by GE, Westinghouse and RCA ended in 1930 with a settlement of an anti-trust suit by the government (which actually gave the Navy what they had wanted back in 1919.) The settlement took patents from GE and Westinghouse (and others) and gave them to RCA. Westinghouse and GE couldn't compete with RCA for two years (until 1933) and RCA was freed of any debt to Westinghouse or GE. This meant that the millions of dollars that RCA owed Westinghouse and GE for the loans necessary to buy the Victor Talking Machine Company didn't have to be repaid. In 1930, RCA Victor became the division of RCA that handled consumer radio and Radiomarine became the division that handled all shipboard radio equipment and operated all of the RCA Coastal Ship to Shore stations.

The RMCA AR-8506-B was introduced during WWII with schematics dated November, 1942 and with the FCC approval for shipboard use dating from February, 1943. The AR-8506-B is a five band receiver capable of reception of LF signals from 85kc up to 550kc and medium/shortwave signals from 1.9mc up to 25mc. The circuit is superheterodyne and uses 10 tubes along with a NE-32 (G-10) neon lamp for voltage regulation (LO.) The IF is 1700kc in order to allow the receiver to cover the entire 400kc range without interruption. Much of the ship's communications were in the frequency range of 400kc to 500kc and a standard IF of 455kc would have a gap in frequency coverage from about 430kc up to 475kc due to the IF operating at 455kc. Usually, shipboard superheterodynes will have IFs that are in the AM BC band area since this region of the spectrum wasn't normally tuned by the ship's communication receiver. The receiver can be powered by 115vdc or 115vac and can also be powered at 230v ac or dc using an external resistor unit, the RM-9. Tuning uses a 30 to 1 reduction vernier drive (counter-weighted) and there is an additional "band spread" function using a separate control. A built-in loudspeaker is front panel mounted and can be switched off by the operator if necessary. These receivers were usually integrated within a shipboard communications console that contained a transmitter, another receiver capable of VLF reception (AR-8510,) an emergency receiver (crystal detector receiver,) a power control switching system that allowed battery operation or ship's power operation and other equipment necessary for radio communication at sea. Most of the RMCA radio equipment was usually installed on Victory ships and other merchant ships during WWII. The FCC approval for shipboard use indicated that the AR-8506-B's LO leakage to the antenna was <400pW and thus would not interfere with other shipboard radio equipment and would not radiate a signal of sufficient strength for enemy DF or detection. The U.S. Army Signal Corps issued a manual, TM11-875, giving the AR-8506-B the designation R-203/SR.

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

The AR-8506-B has an internal 1700kc wavetrap. The wiring and adjustment of the wavetrap should be checked if BC signal leakage is encountered. The wave trap should be adjusted on Band 3 for minimum response with a 1700kc RF signal input to A1 on the antenna input of the receiver. If it is correctly adjusted and still there is BC signal leakage then using an antenna that is "tuned" for the specific frequency desired should be tried. This could be a resonant antenna cut for the specific frequency desired or an antenna with an antenna tuner. The "tuned" antenna will be selective and should reduce the BC interference. Like a lot of RCA receivers, the AR-8506-B doesn't have a standby switch (either remote or panel.) To use as a station receiver requires either an antenna relay with good isolation for the receiver in "transmit" or you can also use an electronic TR switch. Since the AR-8506-B is a "transformerless" AC-DC circuit, always operate the receiver using a 1:1 isolation transformer when powered by the house AC line voltage.

The WWII version of the AR-8506-B is profiled in the "WWII Communications Equipment" page - navigation index at the bottom of this page.


Radiomarine Corporation of America  -  Model AR-8510

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

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

The AR-8510 was approved by the FCC for shipboard use in 1942. The schematic drawings are dated 1943. It's likely that it was at least 1944 before any AR-8510s were in use. The AR-8510 shown in the photo above is the post-WWII version and the photo is from the manual. Like the AR-8506-B, the AR-8510 replaced the round celluloid nomenclature plates and went to an embossed nomenclature panel. Production continued into the 1950s and actual use of the AR-8510 lasted quite a bit longer. It wasn't uncommon to find AR-8510 receivers still being used on old oil tankers as late as the 1990s.

The WWII version of the AR-8510 is profiled in the WWII Communications Equipment page - navigation index at the bottom of this page.


General Purpose Radio Communication Equipment

Wickes Engineering & Construction Co. - Hammarlund Mfg.Co., Inc.  - R-270/FRR

Post-WWII use of the BC-794 Hammarlund Super-Pro - Signal Corps

A constant level signal, free from fading, was necessary for accurate copy of RTTY (Radio Teletype) signals. During WWII, RTTY was being used more and more by the Signal Corps. After WWII ended, the SC continued to develop better RTTY systems. Diversity reception would greatly reduce fading radio signals and provide the nearly constant signal level to the RTTY converter that would allow accurate copy. The diversity system would use widely separated antennas to respond to the different phases of the radio signal at different locations (called Space Diversity) and then the receivers would interact to provide a level of signal reproduction that was constant and based on which antenna-receiver combination was providing the strongest signal. The Signal Corps had different types of WWII receivers modified to allow their use in diversity RTTY systems. Early systems used modified BC-342 receivers. By 1947, the Signal Corps was using modified Hammarlund Super Pro receivers. The initial modification was to improve frequency stability by installing MC-531, a kit that incorporated a three channel, crystal controlled oscillator to the Super Pro. Other modifications required access to the IF output in order to drive the CV-31 Diversity RTTY Converter. When the modifications were finalized, the Signal Corps had Wickes Engineering & Construction Company professionally modify several BC-794 Super Pro receivers (designated as R-270/FRR) which would then be installed into the dual diversity receiver, AN/FRR-12. The AN/FRR-12 would interface with a CV-31A Diversity RTTY converter to drive the TTY machine.

The Wickes R-270/FRR changed some of the tubes in the BC-794 as part of the upgrade. The 6H6 AVC rectifier was changed to a 6SN7 to allow the use of one section (diode connected triode) as the AVC rectifier and the remaining triode to be used as an IF output buffer stage. BFO was changed from 6L7 to 6SL7 and the MC-531 kit added a 6SC7 crystal oscillator to the circuit. Additionally, the BFO could be crystal controlled also, if necessary, for precise reception of RTTY signals. A new aluminum front panel was installed with raised lettering and the steel bottom plate was replaced with an aluminum plate with the receiver schematic printed on the inside. The RA-74 power supply also got a new aluminum front panel and aluminum bottom cover with the schematic printed on the inside. The Crystal Oscillator front panel was installed over the Main Tuning dial escutcheon providing an ON/OFF switch with three channel selection and a separate frequency vernier control. All component nomenclature was redone and the entire chassis given a heavy coating of MFP.

In 1951, Hammarlund released the SP-600 JX receiver that incorporated all of the Signal Corps upgrades along with totally redesigning the entire Super Pro receiver. However, the Signal Corps was also beginning to use the Collins 51J receivers in their RTTY communications. Ultimately, the SC used Collins receivers for RTTY (in most instances) and the SP-600 for general surveillance. 


1950 Collins 51J-2 in original style cabinet. Note the green highlighting of the 40 meter amateur band

Collins Radio Co. - 51J Series
(includes 51J-1, 51J-2, 51J-3, R-388/URR and 51J-4)

Introduced in 1949, the 51J series was developed as a general coverage receiver primarily for military but also for the commercial user or individual/enthusiast providing accurate frequency readout and great stability. Since the earliest versions of the 51J receiver had military designations it's likely that Collins was working with the military to design a thoroughly modern, general coverage receiver that had the requirements needed for dependable RTTY and other data modes of reception. The initial 51J receiver utilized a permeability tuned circuit using the 70E-7 PTO along with a dual tunable IF system and a multiple frequency Crystal Oscillator to cover .5mc to 30.5mc in thirty (1mc wide) bands. The dual tuned IF is switched between odd and even bands (referencing the band number not the frequency.) Three fixed frequency (500kc) IF amplifiers are used. Adjustable selectivity is provided by a Crystal Filter. A standard envelope detector and Noise Limiter are also in the circuit. Band 1 actually is triple conversion but only to allow coverage of the AM BC band. Bands 2 and 3 are single conversion (since they are the output of the dual tunable IF) while all of the remaining bands are double conversion (working with the 10 frequency Crystal Oscillator.) 16 tubes are used in the 51J-1 and J-2. On the early versions, 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 also have a metal dial bezel, the Collins' "winged emblem," no grab handles 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. The most apparent difference between the 51J-1 and 51J-2 is that the latter added an Audio Output function to the S-meter which became a Carrier Level/Audio Output meter that was actuated by a toggle switch next to the meter and the 100kc Crystal Calibrator nomenclature was changed from "100 KC OSCILLATOR" to "CALIBRATE" (though late 51J-1 receivers will have "CALIBRATE" on the front panel.) Some later production 51J-2 receivers may be found with the 70E-15 PTO installed but whether this was a post-sale retrofit or a Collins engineering-production upgrade is unknown at this time. The 51J-1 was produced in very small quantity in 1949 while the 51J-2 was somewhat higher in production quantity being produced from late 1949 thru most of 1950. 51J-1 receivers were supplied to the military as the R-381/URR and 51J-2 receivers went to the military were identified as the R-381A/URR receiver.

In 1950, the updated and improved military version 51J receiver, the R-388/URR, 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 fixed 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 an Antenna Trim control. This revision was probably at the request of the Signal Corps, who found the R-381 (51J-1) or the R-381A (51J-2) difficult to use for some of their teletype installations because of the fixed 300 ohm Z antenna input requirement  (most of the SC installations used either 75 Z ohm dipoles or Lo-Z vertical whip antennas.) Production of R-388/URR receiver was rather high with estimates that well over 12,000 receivers were produced. The contracts started in 1950 but production levels were very small in 1950. The greatest quantity of receivers were produced in 1951, 1952 and 1953. There were additional contracts in 1954, 1955, 1956, 1957 and 1962 but the production levels in these later contracts total less than 1000 receivers. With the R-388, grab handles were added to the front panel along with a high quality Burlington Co. sealed meter although some receivers may be found with a Marion Electric meter (or other makes) installed but whether these were "factory" or a later "field replacement" is not known. Additionally, the 51J-3/R-388 added an internal relay to isolate the antenna and remove plate voltage from the IF section as a Remote Standby function. This addition required the user to provide approximately 12vdc at 135mA to operate the internal relay from the auxiliary contacts on a T-R relay.

Hallicrafters was contracted to build at least two different types of military cases for the R-388 receivers. These cases were made out of heavy gauge steel and featured glides that allowed rollers to be mounted to the R-388 chassis to ease installation and removal of the receiver from the cabinet. A dual receiver cabinet was also produced. The CY-1206/G is shown to the left with a 1952 contract R-388 receiver installed.

A standard phone jack provided 4 Z ohm output and a PL-68 type jack provided 600 Z ohm output both mounted on the front panel on the early versions and later versions had a "Break-in" switch that replaced the front panel speaker jack. Some early receivers were later reworked by the military to replace the front panel speaker jack with the "Break-in" switch.

All R-388 receivers are MFP coated and all have an irradite treatment of the sheet metal used for the chassis and side panels that give the pieces a gold color appearance. However, the side panels are steel, not aluminum (as the R-381s were.)

Nearly all R-388 aluminum top covers will have the receiver schematic on the underside of the cover. Very late R-388s will have the pin jacks on the rear chassis apron for AVC and Diode Load (same as the 51J-4.) 

The serial number that is stamped on the rear of the chassis apron is a Collins' production assigned number that usually was sequential for the entire production however the ID tag's serial number was sequentially assigned for the specific contract only. These two serial numbers never match and considering how they were assigned, shouldn't.

Sometimes an R-388 will be found with both USN Anchor acceptance stamps and Signal Corps acceptance stamps. 

photo above: 1951 contract R-388/URR

The civilian version of the R-388/URR was the 51J-3 which was produced in very limited numbers since the major demand for the receiver was from the military and that demand was satisfied with the R-388. The civilian 51J-3 is seldom seen. These receivers shouldn't have the MFP coating applied since they were going to be in commercial or amateur use. The Collins serial number tag will identify the receiver as "51J-3" and the serial number assigned should be numerically very low.

Be aware that many so-called 51J-3 receivers are actually R-388 receivers with their ID tags removed. Also, be aware that if the 51J-3 data plate has a serial number in the 12000 range, it is a reproduction data plate and the receiver is likely not an authentic 51J-3. If there's no ID tag or a bogus serial number, check the receiver to see if there are any Signal Corps acceptance stamps to verify the model. A 51J-3 receiver shouldn't have Signal Corps inspection stamps or a MFP coating.

The 51J-3 was introduced in 1951 and produced in very limited numbers up to around the introduction of the 51J-4 in 1955.

In 1955, the 51J-4, with 19 tubes and three selectable mechanical filters became available. The 51J-4 added a fourth stage of IF amplification to compensate for the insertion loss of the mechanical filters. The mechanical filter assembly utilized two 6BA6 tubes as input and output amplifiers which, while providing a total of four IF amplifiers, actually only three IF stages are tuned. The bandwidth filters used on the 51J-4 were 1.4kc, 3.1kc and 6.0kc. The filters are quite different physically from the other Collins contemporary receivers in that the 51J-4's are rectangular units that are for 500kc IF rather than the round cylindrical types found in the 75A-4 or R-390A receivers that are for 455kc IF. The 51J-4 also added an adjustment to the overall gain of the IF amplifier section in the form of a chassis mounted potentiometer. The 51J-4 sold for $1099 and despite its expense was still a popular receiver that could be found in coastal stations such as KPH and KMI, in overseas embassies, in commercial laboratories like Beckman, universities like Stanford and even wealthy SWLs and enthusiast-ham set-ups. Some of the very late production 51J-4 receivers can be found with light gray panels and black nomenclature with some even sporting Collins S-line knobs. 51J-4 receivers are not MFP coated. Ultimately, the 51J-4 serial numbers exceeded 7000. Navy catalogs specify an R-388A and R-388B - the R-388 with the mechanical filter assembly installed. It likely that these receivers were probably actually identified on their tags as "51J-4" which would account for the lack of any examples of the R-388A or R-388B.

The 51J-4 was the ultimate evolution of the design but the earlier 51J-1, J-2s and R-388s have their own appeal and can provide top-notch reception. Though thousands of R-388 and 51J-4 receivers were produced, very few 51J-1 or 51J-2 receivers ever turn up indicating that their production was at a fairly low level. Fortunately for those who enjoy using these receivers, the most common version, the R-388, is the best performer providing good quality audio and competitive sensitivity with 1kc dial accuracy.

1957 Collins 51J-4 sn 2392 in original style cabinet (now owned by KB6SCO.)

For the ultimate in detailed information on the entire 51J Series including history, rebuilding and restoration with lots of photographs, go to our web-article "Rebuilding the Collins 51J Series Receivers." Navigation link in Index below


1953 Hammarlund SP-600-25C

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

Officially introduced in 1950 and with production starting in late-1951, the SP-600 was intended for the military and commercial user market. It was a very popular receiver even though the selling price was nearly $1000, but many thousands were built, especially for military applications. It's likely that some of the SP-600 design input came from the U.S. Army Signal Corps, especially the selectable crystal oscillator and the turret band switching sections. The Signal Corps did have some WWII-version Super Pro receivers modified with three-channel crystal oscillators in 1947-49 (R-270/FRR receivers, also other Super Pro receivers with Improvement Kit MC-531 installed - see R-270/FRR section above.) The Signal Corps must have been working with other companies to find acceptable receivers designs for their requirements because, in 1949, the Signal Corps contracted with Hallicrafters to build a "Super Pro-type" receiver that met the design requirements. The Hallicrafters receiver was designated R-274/FRR. The SP-600 was first ordered in a 1950 contract that was for a R-483 receiver (JX-5.) The first R-274A Hammarlund version was on a 1951 contract (JX-1) and this was the first SP-600 officially produced in November 1951. Hammarlund used R-274A and C designations for Signal Corps receivers and R-274B for USN receivers. Hallicrafters versions was assigned the suffix D on the next contract (1952.) Eventually, Hammarlund SP-600s were the choice of the military who ordered tens of thousands of them over the next decade while Hallicrafters' version was not ordered after only two contracts (1949 and 1952.)

Though most Hammarlund SP-600 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 selectable crystal oscillator for maximum stability as the 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 (details on the SP-600VLF version in photo caption below.) 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, different knobs 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 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 selectable 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 VFO position allowed the receiver to operate with the standard LO while the positions 1 to 6 turned off the LO and turned on the Crystal Oscillator while allowing selection of any of the six crystal-controlled frequencies. Although the user could switch to any of the crystal LO frequencies for increased stability for that particular frequency, 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 communications-grade audio with the lower end rolled off at 125Hz 3db down. This audio shaping, while noticeably lacking bass response, was designed into the SP-600 to allow excellent copy in all modes whether it be CW, RTTY (or other data modes) along with greater intelligibility of weak signals in voice modes (either AM or SSB.)

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.

SP-600 VLF-31  -  Shown in the photo to the left is the SP-600VLF-31 receiver from 1955. This version covers 540kc down to 10kc in six tuning ranges and uses 21 tubes. The SP-600VLF is NOT a standard SP-600 with LF coils installed in the turret. The VLF version  uses very different circuitry but with the mechanics and general construction being standard Hammarlund SP-600. The circuit of the SP-600VLF uses a 705kc IF and is a single conversion receiver. Double pre-selection is employed on all bands (two TRF amplifiers.) The "X" option crystal oscillator provides four channels (instead of six) and uses FT-243 type crystals. Five selectivity positions are provided (instead of six.) The 455kc IF output is accomplished by mixing the 705kc IF with a 1160kc crystal oscillator. The 455kc IF was for driving data devices such as RTTY converters. The chassis and the side panels are iridite finish and the side panels are similar to those used on the R-390A receiver. Since the VLF receivers are from the late-fifties, ceramic disk capacitors are used throughout the circuit. 

The SP-600VLF provides tremendous sensitivity and requires a "tuned" antenna for it to operate at its full potential. Generally, a "tuned loop" antenna will greatly reduce the RFI noise that is very high below 500kc and it can also provide directivity that may also help in noise reduction. Nearly all signals in the LF spectrum are now digital data signals or various types of beacons with virtually no voice signals at all.

Best results using the SP-600VLF will require an "RF-quite" location, a tuned loop antenna of reasonable size (minimum 3' diameter) and using a headset for the audio output since many signals are "in the noise" and barely detectable.

The Tubular Capacitor Problem - 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. The decision of whether or not to rebuild an early SP-600 is not really an option - all early SP-600 receivers need to be rebuilt for safe and proper operation.

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

photo right: 1953 Hammarlund SP-600 JX-21


Hallicrafters R-274/FRR sn: 762

 The Hallicrafters Co.  -  R-274/FRR, R-274D/FRR (aka: SX-73)

In the late-1940s, the U.S. Army Signal Corps needed a source of high-quality receiver that had specific Signal Corps design requirements. The main features were a selectable crystal oscillator to stabilize the LO and BFO drift and a rotating turret band switch. Both Hammarlund and Hallicrafters built successful versions of these types of receivers. Although WWII Hammarlund Super Pro receivers had been modified by the Signal Corps to have the selectable crystal oscillator in 1947 through 1949, the quantity of available receivers was limited. The Signal Corps needed a manufacturer that could deliver a new receiver with the specified options in fairly large quantities. Hallicrafters built their receiver on a 1949 contract and it was assigned the designation of R-274. Hammarlund had been advertising their SP-600 since 1948 (as the SPC-600-X) but apparently the receiver wasn't available (or not ordered by the Signal Corps) until 1950. The Signal Corps didn't want to assign a new designation to a similar receiver so the Hammarlund SP-600 was assigned R-274 with suffixes A, B or C used for specific identification. Future R-274 receivers from Hallicrafters would be designated as R-274D.

The typical post-WWII military contract production quantity was probably relatively small, perhaps 1000 receivers per contract. It doesn't seem likely that Hallicrafters would have gone through the effort for one contract. Hallicrafters probably thought there would be many more contracts in the future but that doesn't seem to be the case. The Signal Corps obviously favored the Hammarlund version and literally tens of thousands of SP-600s were supplied to the Signal Corps over the next decade. Since Hallicrafters had invested in some production line tooling and had obviously set up component suppliers for production, they decided there might also be a commercial or even a ham market for their receiver. The civilian designation assigned was SX-73 and these receivers are virtually identical to the R-274D except for the ID tag, which shows "SX-73" as the receiver type. Some advertising mentions that a cabinet was supplied with the SX-73 though advertising artwork generally shows the receiver in the rack mount configuration. Selling price was quite high at $975 which certainly limited purchases of the SX-73 by the civilian market. The SX-73 version is seldom seen and production must have be very limited. The R-274D and SX-73 were available from late-1951 up to around early-1954.

The R-274/SX73 is generally referred to as "Hallicrafters' version of the SP-600" or the "Hallicrafters' Super-Pro" since there are so many similarities between the two receivers. The similarities are to be expected since Hallicrafter's design had to meet Signal Corps specifications (as did the SP-600.) The most obvious similarity is the turret band switch which, while functionally the same at the SP-600's, is not nearly so robust in construction using heavy-duty plastic module bases with stub pins pressing against flex contacts. The SP-600 coils are on a ceramic base with longer pins passing thru dual pinch contacts. The tuning dial provides a main dial and a logging dial as the SP-600 does but behind a single escutcheon rather than separate dials behind two escutcheons as the SP-600 does. There is a selectable six-channel Crystal Oscillator that functions like the SP-600 "X" option and provides improved stability for RTTY and other data modes. Like the SP-600, the bandwidth is selectable in six selectivity steps with three of those steps using a Crystal Filter for narrow bandwidth (a front panel Phasing control is also provided.) A 600 ohm balanced audio output is also similar to the SP-600 audio output.

One major difference between the R-274/SX73 and the SP-600 circuit is the conversion frequency of the SP-600 is 3.955mc while the R-274/SX73 uses 6.455mc. Also, the placement of the conversion frequency with reference to tuning range four has the double conversion starting at 7.0mc on the R-274/SX73 while it is 7.4mc on the SP-600. This results in double conversion being used for the 40 meter ham band on the R-274/SX73 but not on the SP-600.

 The R-274/SX73 frequency coverage of each tuning range is beneficial to the ham user in that 160, 80, 40 and 20 meters are on separate tuning ranges while the SP-600 combines 80 meters at the low end and 40 meters at the high end on tuning range three. In the audio section of the R-274/SX73, the coupling capacitors are .01uf in the R-274/SX73 while the SP-600 uses .0015uf capacitors. This results in the "communications-grade audio" found in the SP-600 while the R-274/SX73 has a more conventional audio response. Additionally, the R-274/SX73 provides an Antenna Trim control while the SP-600 does not. Possibly the most important difference between the R-274/SX73 and the SP-600 is that the former receiver utilizes almost entirely ceramic disk capacitors in the circuit rather than the "leakage-prone" molded capacitors that have negatively influenced the reliability and reputation of all early SP-600 receivers. In considering the restoration of the R-274/SX73, the ceramic capacitors will certainly and positively reduce the amount of rework that is going to be necessary.

Some of the components used in the R-274/SX73 are of a better quality than those found in the SP-600 - IF transformers and the bulk of the capacitors used, for example. But some other parts and components are not as high of quality as those found in the Hammarlund - band switch turret, the dial gear train and the dial lock, for instance. The R-274/SX73 tuning condenser bearings are very poor quality and can rust excessively in a humid environment which can cause "sticking" and "jamming" of the tuning condenser's rotation. The R-274/SX73 tuning dial itself along with the logging dial are difficult to read (some users find the same fault with the SP-600) and the R-274/SX73 dial illumination is subtle while the SP-600 illumination is dazzling. The Carrier Level meter has only a Decibel scale that references 0db as mid-scale on the meter which is equal to 50uv input signal level. Performance is the final judgment though and the R-274/SX73 will easily provide the user the same high sensitivity and quality reception as the SP-600 along with much better sounding audio reproduction.

photo above: The R-274 mounted in its military table-top cabinet, the CY-699/FRR



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