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COMMERCIAL & MILITARY  COMMUNICATIONS  EQUIPMENT

1932-1941   &   1946-1959

 

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


 Illustration:  From Signal Corps TM11-688 showing the operation of the TRD-4 Direction Finder that utilized three R-390/URR receivers


Commercial & Military Communications Gear - 1932-1942 & 1946-1959

1932 - 1942

 

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. 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. The frequency coverage is 1500kc down to 15kc in seven tuning ranges. Power is supplied by batteries. Like earlier designs for shipboard receivers, e.g. the IP-501-A, the Mackay 105-A utilizes an LC Antenna tuner ahead of the regenerative detector to increase gain and selectivity. An Antenna Series Condenser switch selects various value capacitors to match the ship antenna to the receiver input and a stepped Tone control provides some relief from static. The panel meter is a dual meter that normally reads filament voltage but B+ voltage can also be monitored by activating a panel switch. The left large tuning knob tunes the Antenna Condenser, the middle large knob controls the Regeneration Condenser and the right large knob tunes the Detector Condenser. The Mackay 105-A is built for shipboard use being physically stout and very heavy. Originally the receiver was panel mounted in one of the Mackay Marine Radio Units that housed the majority of the radio gear for the ship. (See our "Vintage Longwave Receivers" webpage for an in depth article about this receiver.)

Mackay Radio & Telegraph Co. - Type 102-B Frequency Monitor

 

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

 

 


1932 - RHM Airport Receiver

National Company, Inc.  -  RHM

In 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. 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 communications 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 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 - all of these features were to become standard for National receivers over the next several years. Since the RHM was a commercial airways 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 is 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 is 500kc. It's likely that less than 100 RHM receivers were built and only a few survive today since most of the airport equipment was scrapped when it became obsolete.

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 ham use and dubbed it the AGS. The AGS was upgraded with newer tube types and other changes during its short production life (probably two or three production runs totaling no more than 300 receivers.) The major change was with the introduction of the AGS-X which added a front panel BFO control and  a James Lamb type crystal filter to the receiver. In 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, not many hams could afford it. If the ham really wanted the AGS-X he could wait for the introduction of the HRO (in early 1935) at which time Leeds was selling the AGS-X for $123. Or, if the ham couldn't wait, he could opt for the Hammarlund Comet Pro, the only other commercially built shortwave superhet available at the time. Actually, the Comet Pro was only $155 (and it had a built-in power supply) but it didn't have an RF stage and required an external pre-selector for image-free reception above 10mc. The Comet Pro came out in 1931 and, from 1932 up to about early 1934, only National and Hammarlund were offering commercially-built, shortwave superhets.

I have owned the RHM shown above since 1990. It is all original and has its complete original coil set (15 coils) in the original rack mounted coil holder. In March 1933, Radio News published an article by James Millen titled "Testing a Modern Superhet" that described National's procedure for testing and aligning the AGS receiver. In the article there was a photo of the Radio News' AGS set-up that showed they were using a National Dog House power supply and a set of Hi-Z 'phones for the audio output. I've been running my RHM in this fashion also, using a National 5886 PS (6.3vac Filament and +180vdc B+) and then listening on a pair of Type-C Navy Baldwin 'phones. This has given me the best results, although if I don't want to use the "Baldies," I can connect up a Hi-Z magnetic cone speaker like a Radiola 100A which then eliminates the need for an audio output transformer and provides ample volume (the Hi-Z speaker solenoid coils connect between AF plate and B+ - just like an audio output transformer.) The RHM functions quite well with 75 year old components - every part was the best that was available at the time. Today, the RHM performance seems antiquated and crude but in 1932 it was "state-of -the-art" and the fact that the receiver is still operating and is still fairly accurate in its 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.

 


National RCF-2 ca: 1940

National Co., Inc. - Airway Communication Receivers (Modified NC-100 Receivers)

National Co., Inc. had been supplying receivers for airports 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 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. With the developing navigation systems that allowed flying an airplane to an airport via the "beam" and also to allow two-way communications with pilots in addition to weather reports, newer and airway-specific equipment was going to be required. 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. In 1937, National began supplying the Department of Commerce (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. 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. After WWII, early versions of these receivers were again 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. 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 CAA Airway Communication Receiver is 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. The Airway receivers use a 3/16" thick aluminum front panel that is black wrinkle finished. All Airway receivers were equipped with an I.N.S. control. I.N.S stood for "Interchannel Noise Suppressor," which was actually a "squelch" control. 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 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 CAA receivers although it is possible that a few were so equipped. The chassis is covered top and bottom with a "slide on" dust cover. 12 tubes are usually used in the circuit which utilizes a 457kc IF. Some later receivers may be found modified with Non-OEM Crystal Filters or variable coupled IF transformers. Shown in the photo above is a 1940 Airway Communication Receiver Type RCF-2 S/N 13.

 


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

Radio Corporation of America (RCA) - AR-60

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. 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., who 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 more than likely "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 PanAm 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. 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: http://oldcoasty.info

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 until a tuning chart is made or the dial readings learned for specific frequencies. It is awkward that the 80 meter band is split with the section below 3.8mc tuned on range 2 and the section above 3.8mc tuned on range 3, however, the AR-60/CGR-32-1 was really never designed as a ham receiver. 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, go to our web-article "RCA's Legendary AR-60 Receiver." Link below in the Navigation Index.
 

 


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 greatest communications receiver creation was the AR-88. Designed in 1940-41 by Lester Fowler and George Blaker, 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.

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.

photo right: Early version of the CR-91 variation of the AR-88, ca. 1945

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.


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 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. 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 header 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.

 

1946 - 1959

 

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. The purple (when illuminated) dial provides a unique visual experience when tuning in the various signals. Selectivity is controlled by a combination of the RF Gain setting and the setting of the Regeneration. The 3001-A is very sensitive and capable of receiving any of the NDBs and other LW stations found in the spectrum below 500kc. These type of Mackay receivers were in use for several decades and were commonly found still operating on commercial ships as late the 1990s. These 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.)

 


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." 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.


 R-388/URR from a 1951 contract. "CAUTION" tag is missing. CL meter is Marion Electric alternate for Burlington

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 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.

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' assigned number that usually is sequential for the entire production however the ID tag's serial number is sequentially assigned for the specific contract only. These two serial numbers never match and considering how they were assigned, shouldn't.

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. Some 51J-3 receivers do turn up and their ID tags will identify the receiver as such, however be aware that many so-called 51J-3 receivers are actually R-388 receivers with their ID tags removed. The 51J-3 was introduced in 1951 and produced in limited numbers up to around the introduction of the 51J-4 in 1955.


1957 Collins 51J-4 sn 2392 in original style cabinet

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. The photo to the left shows a mid-production 51J-4 sn 2392 from around 1957 that was formerly owned by Stanford University. 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 and R-388 were the ultimate evolution of the design but the earlier 51J-1 and J-2s 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.

For more information on the 51J Series including rebuilding and restoration go to our web-article "Rebuilding the Collins 51J Series Receivers." Navigation link in Index below

 

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 IF amps were changed from 6K7 to 6SK7, 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 1950, 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. 

 


1953 Hammarlund SP-600-25C

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

Officially 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. 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.) Also, the Signal Corp accepted a similarly designed receiver from Hallicrafters in 1949. The Hallicrafters receiver was designated R-274, as was the Hammarlund SP-600. The SP-600 used suffixes A, B and C while Hallicrafters used suffix D. Though most versions were built throughout the 1950s, the SP-600 continued to be produced in smaller numbers up into the early 1970s. The standard SP-600 tunes from .54 to 54MC in six bands. A "J" suffix indicates JAN parts were used in the construction and an "X" suffix indicates a 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. Hammarlund made over 40 variations that were assigned a numerical suffix which identified the particular circuit, mechanical changes or sometimes the end-user. The last in the "time-line" was the model variation SP-600 JX-21A from 1969-1972 which utilized a product detector circuit, two additional tubes and some other changes to make it "compatible" with SSB operations.

Most versions use a 20 tube double conversion superheterodyne circuit with a rotating turret bandswitch. The receivers also feature enormous proportions, robust construction and oversize controls - along with a super-smooth tuning system that only adds to the enjoyment of operating these fine receivers. Double conversion is switched in above 7.4MC and uses a crystal controlled conversion oscillator. Though the SP-600 has two dials, it has no bandspread - the right side dial is a logging scale allowing precise retuning of desired stations. On the left is the main tuning dial and the mechanically articulated dial pointer that indicates which tuning scale is in use (along with the small window between the dials that shows which tuning range is selected.) The tuning arrangement was an up-dated version of the "Continuous Bandspread" system introduced in RCA's AR-88 series receivers in the 1940s. The frequency readout accuracy is vague which is why a precise logging scale system is incorporated into the SP-600 design. The 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 impressive 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 great 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.


1953 Hammarlund SP-600 JX-21

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

The inset photo shows the SP-600 JX-21 version from 1953. The JX-21 was generally used by the USAF. This is the early version of the JX-21 - so it does not have the product detector SSB changes. The header photo shows the SP-600-25C built for the US Army Signal Corps and it is housed in an original SP-600 cabinet. The SP-600-25C version has the large square 25-60 cycle power transformer and does not have the switchable crystal oscillator ("X" option.) SP-600 cabinet colors vary from dark charcoal to light gray depending on when they were manufactured. A rebuilt SP-600 is a pleasure to operate with incredibly smooth tuning, competitive sensitivity, a great selectivity set-up featuring six positions that include three crystal filter positions and, of course, its massive controls and domination of the ham station landscape.

  

 the Hallicrafters, Inc.  -  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 features. 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 submitted successful design. 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 a fairly large quantity. Both Hallicrafters and Hammarlund submitted designs that were accepted. Both receivers were given the same Signal Corps designation, R-274. The early Hallicrafters receiver was produced with the R-274 designation as were early Hammarlund SP-600 receivers. With the contracts that followed, Hammarlund was assigned the suffixes of A, B and C to specifically identify their versions. With their second contract, Hallicrafters was assigned R-274D, adding the D suffix to specifically identify their version.

The typical military contract production quantity was for around 5000 receivers and it doesn't seem likely that Hallicrafters would have gone through the effort for a smaller contract. It's also possible that Hallicrafters thought there would be more contracts in the future but that doesn't seem to be the case. The Signal Corps apparently 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 fiber board modules while the SP-600's are made of ceramic. 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. 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 6.000mc. 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 the 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-274D 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 feeble. 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.

 


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

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

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

 

photo above: 1955 Collins R-390A. Who knows what the "37.4" stencil means? (I don't.)
 


Collins designed a replacement receiver that was introduced in 1954 with the designation of R-390A/URR. Though the new receiver looked very similar externally to the R-390, inside numerous changes were made to improve cost-to-performance and ease of maintenance. The new receiver's gear box was removable as a unit and synchronization would be maintained, the crystal oven just plugged into the Crystal Oscillator module (it is secured by screws though,) the B+ voltage regulator circuit became a standard 0A2 tube, the crystal calibrator was combined into the RF module (eliminating the separate Crystal Calibrator module of the R-390) and the Crystal Oscillator module was mounted to the RF module so removal of the entire RF deck kept everything synchronized together except the PTO. Most of the maintenance "quirks" of the R-390 were corrected in the R-390A. The major performance change involved the installation of four mechanical filters in the IF section of the receiver. The steep slopes of the mechanical filters gave the R-390A excellent selectivity on 16KC, 8KC (really about 11KC,) 4KC and 2KC bandwidths. The 1KC and .1KC bandwidths are crystal filter derived from the 2KC wide setting. The R-390A uses 26 tubes (including the 3TF7 ballast tube) with one RF stage, four IF stages, mechanical filters on four of the six selectivity positions, plus an 800Hz audio filter. When properly set-up, one can dig right through the QRM while maintaining fantastic sensitivity making the R-390A one of the finest tube-type receivers ever built. However, some ham AM operators find the audio on an R-390A to be a bit harsh due to "ringing" in the mechanical filters. The R-390A was produced in yearly contracts from 1954 up through 1967 (and a very small contract in 1984) with many different contractors building the receivers during those years. Though the R-390A's six modules and redesigned maintenance approach made field repairs easier, it was still a complex receiver. Though the military wanted a less expensive receiver, it certainly wasn't that either.
The R-390 and R-390A receivers have provided reliable communications under adverse conditions for years and even though the designs are over 50 years old, they are still one of the best tube-type receivers around. Many R-390 and R-390A receivers are still being used today, some in professional applications, but also for serious SWLing and, of course, in vintage ham stations around the world. Many AM operators prefer the R-390 version for its better over-all sound quality when listening to SWBC or AM stations in general, however one must consider the maintenance challenges when selecting the R-390 for a station receiver. Nowadays, many R-390 and R-390A receivers are being used in "as purchased" condition - that is, the receiver has not been rebuilt, restored or even thoroughly serviced and properly aligned (or is it "alined?") The performance of a fully functional, rebuilt (restored) and recently aligned R-390/390A is incredible. 

Contemplating rebuilding an R-390A? Go to our web-article "Rebuilding the R-390A Receivers" for easy to follow information and lots of photographs. Link below in the Navigation Index.

 

photo right: Motorola 1956 contract R-390A. The early  Collins and Motorola panels had silk-screened nomenclature rather than engraved nomenclature. By 1957, all front panels were engraved.


1961 contract manufactured by Capehart with OD front panel

R-390A  - End-User Front Panel Repaints

From time to time, R-390A receivers will show up with the front panel sporting a non-standard paint color. The original specification only calls for the panel to be painted gray. Consequently, many shades of gray are found from the many different contractors that built R-390As over the years. Sometimes though, completely non-standard colors will found and these are always "end-user" applied paint jobs. The most commonly known "end-user" paint job is the USAF's flat-black panels (see photo below.)

Several years ago, a 1961 Capehart contract R-390A with an olive drab painted front was found in the Northern Nevada area. It had been supposedly repainted by the USMC. Here is another 1961 Capehart with the OD painted front panel, also found here in Northern Nevada, in 2009. Also, North Korea has made the U.S.S. Pueblo into a museum. The ship had many R-390 and R-390A receivers onboard. There is a color photo on the Internet that shows some of the receivers from the U.S.S Pueblo and two of the R-390A receivers appear to have OD panels. All R-390A receivers left the contractor's facility with gray panels - it was the specification - but the "end-users" were liable to repaint during a rebuild so anything might be possible - just not original.

This is probably the best known photograph of R-390A receivers sporting end-user front panel paint jobs. The installation shows banks of R-390A with dark panels, presumably "flat black" paint. Note that many (not all) of the receivers have severe wear on the Kilocycle Change and Megacycle Change knobs indicating continuous operation of the sets. Most of the racks have Teletype machines associated with them. This photo was of USAF Morse Hall at Clark Air Force Base in the Philippines.    

 

 

photo from: sites.google.com/site/cobradensite/usafss-history-by-ron

 

R-390A - "Blue Stripers"

When some of the military R-390A receivers were decommissioned, they were sent to a facility located in Portsmouth, Virginia called St. Julian's Creek Annex. At this repository, thousands of derelict R-390 and R-390A receivers were piled one on top of another and stacked side by side on pallets. The receivers typically had their meters removed (due to the radium used on the needles and the scales) and usually the data plates were also removed. Many times the top and bottom covers were already missing. Sometimes receivers were found that still had their meters installed. The story goes that the meters were checked for radiation levels and removed if the reading exceeded a predetermined level. If the radiation level was below the spec then the meter was usually "tagged" with a stick-on paper dot. The final indication that the receiver was "ready to scrap" was to brand it with a "blue stripe" that was generally applied from a spray paint can. Many times, yellow paint was used but the use of blue paint has accounted for the moniker - "Blue Striper."

These receivers were left out in the weather with no protection whatsoever. The receivers that were in the middle of the vertical stacks generally faired best while the receivers at the top of the pile got all of the rain, snow, sun and dirt. The duration of the storage depended on when certain pallets were sold off. At one time, the receivers sold for as little as $37.50 per receiver, taking into account the entire pallet had to be purchased. Apparently, over the years, R-390As came and went at St. Julian's Creek Annex. Some receivers may have been sold in small lots but the majority were sold by the pallet. It appears that well into the 21st century, R-390A receivers were still being sold from St. Julian's Creek.

Some of the R-390A receivers sold by Fair Radio Sales in Lima, Ohio were "Blue Stripers" from St. Julian's Creek Annex. The Fair Radio Sales' "Blue Stripers" were the ones that were sold as "needing some work" - maybe a bit of an understatement. Selling price was an incredible $330 in the 1990s. It's generally thought that Fair Radio Sales would put together the "needing some work" R-390As from various condition "parts sets" and "used spares." Consequently, most (if not all) Fair Radio "Blue Stripers" are not true St. Julian's Creek R-390As and probably only have some parts that came from the annex.


St. Julian's Creek Annex - piles of R-390As

 The R-390A shown above was sold by Fair Radio Sales many years ago and, after its purchase, it sat for many more years in a garage in the San Francisco Bay Area. It was donated to the museum in 2011 by NU6AM. Note that the panel was repainted a non-original very light grayish-white and the nomenclature has been filled in black. Additionally, this receiver has a Raytheon PTO dated 1977. I would think that this is probably a Raytheon rebuild of a Cosmos PTO. Overall, the condition of this "Blue Striper" is surprising good. Of course, none of the modules match (contractors) which seems to confirm that Fair Radio did "put together" this receiver from parts. What is odd is that they would go through the trouble to assure that relatively good condition modules were provided and then use a "Blue Striper" front panel. At the moment (2011,) the receiver is non-functional but updates on its condition will be forthcoming.

Update 2013: Unfortunately, like a lot of receivers in the condition that this "Blue Striper" is in, this one has become a source of parts to restore other R-390A receivers that have faired better. The RF deck has gone into a 1962 Teledyne R-390A, the IF module has a bad 4kc mechanical filter but may donate the MF tuners to another IF module. The PTO is going into the 1961 Capehart. The ON/OFF microswitch went to repair an Amelco R-390A. It is unfortunate but parts are what keep other R-390A receivers in "top condition" so they can be operated and appreciated for the incredible performance they provide the user/owner.

 


GRC-19 mounted on the MT-851/GRC-19 vehicular shock mount with LS-166 loudspeaker and H-33 Handset

Collins Radio Co. - AN/GRC-19

GENERAL INFORMATION - Around 1951, the U.S. Army Signal Corps needed a portable transmitter-receiver combination that was modern, operated at a moderate power level and could be used outdoors or even deployed via parachute to remote locations. The result was the GRC-19, a set-up that consisted of the T-195 transmitter - an autotune unit capable of around 100+ watts of carrier power - and the R-392 receiver that was based on Collins' the highly successful R-390 receiver. Since the transmitter-receiver had to be portable, it was designed to operate exclusively on +24vdc to +28vdc. Since the GRC-19 was going to be exposed to the weather in many types of open vehicles, the entire system had to be somewhat "weather proof." To allow the receiver to be completely sealed with no ventilation and thus, to have the receiver run as cool as possible, no voltages higher than +28vdc are used in the R-392. The T-195 transmitter used forced-air cooling for the three external-anode tubes used in the PA and Modulator so an air filter was provided for the intake but this did not "water proof" the transmitter while it was in operation. It was possible to seal the intake and exhaust ports when the transmitter was not in use to aid in the weather-proofing. Additionally, many times the military was going to have to "drop" communications gear from the air, so the R-392 and T-195 had to be "ruggedized" to be able to survive this type of deployment for portable field use (the usual drop was a fully-equipped Jeep that included the radio gear.) The GRC-19 was commonly used on Jeep-type vehicles up to larger "command car" types. A whip antenna was used if operation was going to be mobile but, if the vehicle was going to be in one location for longer than an hour and a half, a dipole antenna was usually erected since power output was much better with this type of antenna. Although generally thought of as an "army radio," the "AN" designation implies "ARMY-NAVY."  Additionally, the Air Force had its own technical manual designation (TO 31R2-2GRC19-11) so the GRC-19 was used by all branches of the military for various purposes from the early 1950s up into the late 1970s.

 T-195 (GRC-19)

The transmitter for the GRC-19 set-up was the T-195, designed by Collins Radio Co. around 1951. The T-195 is a 100+ watt carrier output transmitter capable of AM, CW or FSK transmission on frequencies from 1.5mc up to 20.0mc. Seven preset frequency channels are available along with a Manual Tuning position that can also serve as an eighth preset channel. The transmitter is built onto a main frame with modules that plug into various Amphenol-type sockets and inter-module contacts to provide power and signal routing. The circuit uses a PTO to generate an oscillating signal that is fed into an Exciter-Multiplier module that mixes the signal to the correct output frequency. As expected from Collins, the PTO and the Exciter-Multiplier are permeability tuned with the Exciter-Multiplier using a slug rack and RF transformers that are very similar in appearance to the R-390A RF transformers. The Exciter-Multiplier has a 5763 output tube that drives the PA module that has a single 4X150D external anode type RF amplifier output tube along with a built-in discriminator circuit to control the automatic Plate tuning of the PA tube. The Modulator module contains the speech amplifier and the push-pull 4X150D modulator tubes and the modulation transformer. The output loading and matching is all accomplished automatically by using a Discriminator module, a Servo Amplifier module, an Antenna Capacitor module, an Antenna Inductor module and the Output Capacitor section that is part of the Main Frame. A total of 21 tubes are used in the T-195 which features complete autotune capabilities and uses a Veeder-Root type of mechanical-digital readout for the transmitter frequency. Modes available were AM VOICE, FSK or CW. Additionally, the T-195 can be set-up as a RELAY station by using the R-392 receiver audio to drive the T-195 audio input and thus "relay" an incoming signal.

1952 T-195 Transmitter built by Stewart-Warner for Collins Radio Company. This particular T-195 has been upgraded to have the +HV Solid State power supply rather than the original dynamotor. After this modification the transmitter was usually designated as T-195A.

T-195 Circuit Details - Inside the T-195 are several small DC motors. Two motors operate blowers to provide forced air-cooling for the three 4X150D external anode tubes used in the PA and Modulator (4X150D - the "D" version must be used since it has a 26.5vdc filament.) Another DC motor is the autotune motor which operates the channel preset frequency selection. The Output Capacitor selection uses a DC motor. There are three AC servo motors (operating on 115vac 400~) to control the loading and tuning operation which is also part of "autotune" in that the T-195 does "automatically tune" itself to whatever antenna load is connected. This "tuning" is accomplished by using a discriminator module that creates error voltages based on phase and load sampling (of the PA) which are then amplified to drive the servo motors. When the error voltages are zero then the transmitter is "tuned" to the antenna load. On early T-195s, two dynamotors are internal to the transmitter with a HV dynamotor providing +1000vdc and a LV dynamotor that supplies three voltages, +250vdc B+ along with -45vdc for bias requirements and 400 cycle 115vac. Additionally, there are several thermo-switches to prevent overheating along with relays and interlocks galore (there are over 15 relays used in the transmitter.) The T-195 is very complex because of its autotune capabilities and because it was designed to essentially be used by operators with no particular skill or training, thus the transmitter had to basically "take care of itself." Several of the thermo-switches will shut down the transmitter if things get too hot. A few minutes "cool down" is normally required to let the thermo-switch reset (you should also correct the problem that caused the over-heating in the first place.) The T-195 is robustly built so reliability was usually pretty good. The photos below show the densely-packed modular design and the complexity of the T-195.

T-195A and B Versions - Late in the military's use of the T-195 (just before the Vietnam War era) there was a retrofit to convert many of the T-195 transmitters to use a solid-state power supply to replace the +HV dynamotor. The replacement power supply is shaped somewhat like the original dynamotor but has no vent holes or any moving parts. This reduced the total transmitter current required down to about 35amps but the big reduction was in the +HV dynamotor "starting current" that no longer was required. Later, a solid-state power supply for the +LV dynamotor was also available. Still later, these SS power supplies were installed from the factory and these models will be designated as the T-195A or T-195B. Although it's likely that the A version has just the +HV PS and the B version has both, I can't find any documentation that states this is the case.


A look at the T-195 upper deck. On the left side is the PTO and Exciter-Mulitiplier. Clustered in the center are the Discriminators, Antenna Capacitor and inter-connecting sockets. On the right side is the Antenna Inductance module and to the front of it is the Output Capacitor selector. Just visible on the lower deck is the back of the LV dynamotor (with the vents) and below the Antenna Inductance module is the +HV SS PS.


Looking at the underside of the T-195. At the upper left is the Modulator module. Note the yellow captive screws that indicate that this small chassis is removable to allow installation of new modulator tubes. The black cylinder is the +HV SS PS. The module in the center is the Servo Amplifier. The RF PA module takes up most of the right side of the bottom deck. The air variable is the plate tuning capacitor that is servo motor driven during the autotune cycle. Upper right just below the Amphenol socket is the RF PA blower housing.

R-392/URR (GRC-19)

Circuit - A stout, small and fairly lightweight receiver, the R-392 still has a lot of the features found on it's big brother, the R-390. Frequency coverage is .5mc to 32mc in 32 tuning ranges each with 1mc of coverage. Permeability tuning using slug racks driven by a complex gear train with a PTO, variable tuned IF and fixed Crystal Oscillator providing double and triple conversion is very similar to the R-390 receiver's front end as is the frequency read out provided by a Veeder-Root digital counter. 25 tubes are used in the double and triple conversion circuit that also provides 2 RF amplifiers and 6 IF amplifiers. Also, the IF stages are similar to the R-390 in that mechanical filters are not used for the selectable 8kc, 4kc and 2kc bandwidths. Data modes, e.g., portable RTTY, could be received via the IF output connector (the T-195 was capable of FSK transmission.) The Audio Output is 600 Z ohms and accessed from either of two twist-lock type connectors marked AUDIO or it can also be accessed from the POWER INPUT-TRANS CONT (PI-TC) connector. There is no phone jack on the R-392 because in the GRC-19 configuration the audio was routed to the T-195 (via the PI-TC connector) where typically a telephone handset, the H-33, was used for both transmit (microphone) and receive (earpiece.) The typical field speaker, if used, was the weather-proof LS-166. A Noise Limiter circuit is activated with the Function switch and a Squelch function is also available. When operated as the GRC-19 there is a short interconnecting cable between the T-195 transmitter and the R-392 receiver using the PI-TC connector that allows the two units to function together with the T-195 providing Break-in or Stand-by functions along with receiver to transmitter Signal Relay capabilities.

Variations in the R-392 Receivers - The initial contract in 1951 was from Collins Radio Co. but soon, just like the R-390 and R390A, many other contractors built the R-392 receivers. There are some variations from early production to the later receivers. Early receivers will use 26A6 tubes for the RF amplifiers while later production used an improved version of that tube, the 26FZ6. The change to the 26ZF6 was to help with cross-modulation problems when using the receiver near operating transmitters. Most of the later manuals specify that either the 26A6 or the 26ZF6 can be used as RF amplifiers. Early panels have silk-screened nomenclature while later panels are engraved. The 2kc-4kc-8kc BANDWIDTH nomenclature layout is closer together on early panels but spaced at 90 on later panels. Cabinets on early models have large flutes that run front to back while later cabinets have five "ribs" that entirely encircle the cabinet running parallel with the front panel. These "ribs" strengthened the cabinet significantly. Like many contractor-built items, the color tint of the olive drab paint used varies from contract to contract with some receivers appearing very light brownish-OD while others appear dark greenish-OD. R-392 production ended in the mid-1960s.


1963 Western Electric R-392/URR

More Information on the GRC-19? For the ultimate in details on repairing, rebuilding and operating the AN/GRC-19 go to our web-article "Rebuilding and Operating the AN/GRC-19" - navigation link below in the Index

 

 

Barker & Williamson
for U.S. Army Signal Corps

T-368/UTC

By the early 1950s, the popular Signal Corps version of Hallicrafters' HT-4, the BC-610, was rapidly becoming outdated and a modern replacement was needed. The T-368 transmitter was designed to fill similar needs for a medium power, continuous duty transmitter that could be placed in communications huts, set up for mobile operation from a truck or set up for stationary operation. The design allowed for 400 watts to 450 watts of RF power to be delivered to a full size antenna or to a mobile whip antenna. The RF output tube is a 4-400A that is modulated by two 4-125A tubes. Similar to the T-195 design, a PTO is used to drive a Multiplier/Exciter module which in turn drives the RF output tube. Also, like the T-195, a Veeder-Root type of digital counter is used for the frequency readout. Vacuum variable capacitors are used in the Pi-network since the +HV is around +2500vdc. Unlike the T-195, the T-368 is not an "auto tuning" transmitter and must be manually tuned for proper matching to the antenna load impedance.

The T-368 will transmit in AM voice, CW or FSK modes. It can also be used as an RF amplifier using the External Input. For FSK RTTY operation, a proper FSK driver is necessary and is connected to the FSK input on the front panel. Voice generally used a M-29 carbon microphone with the CARBON MIC input but this isn't strictly the only way to voice modulate the transmitter. You can also run audio into the 600 OHM input via the rear Remote connector. Though intended for use with telephone inputs, the 600 OHM input is exactly the same electronically as the CARBON MIC input with the exception that the bias blocking capacitor used in the CARBON MIC circuit is not present. The disadvantage to using the 600 OHM input is that the mike cable must be routed to the back of the transmitter. By using the 600 OHM input, a crystal or dynamic mike can be used resulting in improved quality audio.

The T-368 is heavy - around 600 lbs. It's large - around 30"W x 40"T x 24"D. Generally, the T-368 is found mounted on the military moving dolly that has large casters along with lifting holes for a military moving hoist. To remove any of the three decks is arduous work, with the PS section weighing nearly 200 lbs. The T-368 usually requires two men to disassemble or reassemble due to the massive size and weight of the component parts. However, this "heavy-duty" approach makes the T-368 nearly "bullet-proof." It was designed for continuous operation and is generally only "coasting" in amateur service.

 

Zenith Radio Corp.
for U.S. Army Signal Corps

R-520/URR  &  R-520A/URR

 

photo left: R-520/URR (H-500 Series TO)

photo right: R-520A/URR (600 Series TO)

 

 

Moral radios, that is radios specifically made for entertainment reception by military personnel, have been around since before WWII. It's not surprising that the Signal Corps wanted something for the soldiers to listen to during the Korean War. The Zenith Transoceanic was a very popular portable AM-BC and SW radio with Zenith cranking out well over one hundred thousand units by 1952. It seemed like a natural choice for a moral radio. >>>

>>>  A few changes had to be incorporated into the basic H-500 style, five tube TO. A neon pilot lamp (a power on indicator) was added. The band selector switch information was color coded. Increased shielding was added. The black stag covering was replaced with a brown vinyl oil-cloth covering. Additionally, "USA" was stamped in Signal Corps orange paint on all sides of the cabinet and a metal data plate attached to the front below the latch. This was the R-520/URR "Transoceanic" that was produced for the Signal Corps. About 5000 units were built but by the time Zenith finished the contract and had shipped the R-520s out, the Korean War was over. The Army decided to give a majority of the R-520s to the PXs at various bases around the country. The idea was to rent the TOs out to soldiers for use at their base housing or in barracks. Many were rented and never returned. Some made it the surplus market. Some had the orange "USA" removed along with the military data plate to make the TO look more civilian - especially if it was one that was rented and never returned.

Around 1961, the Army was planning the Bay of Pigs invasion. A contract for special "air drop" cases for the R-520 was issued with a quantity of between 250 to 500 units. These were designated for the R-520 but it's probable by that time the R-520 had been replaced by the R-520A version. The same sort of changes were incorporated into the new R-520A military version with a neon bulb pilot lamp, tube shields, removal of the fold-down log book, no front headphone jack, no dial lamp switch and "USA" was stamped into the back of the chassis. A schematic and instructions were glued to the inside back cover alond with two fuse boxes and a Signal Corps TM manual. The black stag of the civilian model was replaced with an olive drab colored oil-cloth type covering and the orange "USA" stamped on the left side of the cabinet. Some will have an orange Signal Corps acceptance stamp on top of the cabinet. This model was designated as the R-520A/URR. It was still the basic five tube TO but, as with all 600 models, this one also had a ballast tube to compensate for low battery voltages. Zenith produced around 3000 units, making the R520A the lowest production TO. The need for more moral radios in the early 1960s was dubious so its likely that the Army went through the same procedure to make use of the R-520As with the same end results. Many are found today with the orange "USA" removed along with the military data plate, for obvious reasons. There is some speculation that some of the R-520A TOs were used in Vietnam but this is only speculation. Certainly, both of the military versions of the Zenith Transoceanic were very low production with likely only one contract for each model.

 

Nems-Clarke, Inc.  -  1302 Special Purpose Receiver

Allen Clarke started in the electronics design business in the 1940s and by 1951 had a small electronics design business. NEMS was an acronym for National Electric Machine Shops, a name chosen by NESCO, National Electric Supply Company, when they incorporated in 1937. NESCO goes back to 1899 and the company was involved in radio manufacturing very early with many contracts assigned to them in WWI and after. NEMS and Clarke merged in 1955 as Nems-Clarke - specializing in high-end commercial-military radio equipment. All (?) Nems-Clarke receivers operate in the VHF and UHF part of the spectrum that was then being used in part for telemetry from some kinds of missiles and for other military and quasi-military purposes. Later Nems-Clarke receivers monitored Russian missile launch telemetry. The 1302 Special Purpose Receiver is a VHF AM/CW/FM receiver that utilizes a Western Electric 416A Planar Triode tube in the front end. The 416A operates at a very high temperature and is cooled by a small forced-air blower. The receiver tunes from 53mc up to 262mc in one continuous coverage tuning range with a 0 to 35 scale for logging. The tuning dial is not illuminated. Behind the grille on the left side of the panel is the built-in four inch speaker. The 1302 was designed to operate with a matching Spectrum Display Unit, (SDU) or Panadaptor.  The upper zero-center meter is for tuning FM and the lower meter shows relative signal strength and can be used for tuning AM signals or measuring relative FM signal strength. The 1302 was primarily used for surveillance by several different government users. Later versions of the 1302 use a different front-end tube (7007) and are styled more like the Nems-Clarke receiver shown below.

 

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

Nems-Clarke was purchased by Vitro Electronics in 1957. Nems-Clarke/Vitro continued to produce Special Purpose Receivers for surveillance and telemetry that were used throughout the late fifties and sixties. The 1306-B Special Purpose Receiver is a 29 tube AM-FM-CW receiver that was usually operated with a SDU-200-6 Spectrum Display Unit (panadaptor.) The receiver tunes 30mc to 60mc and 55mc to 260mc with separate dials for each band that are only illuminated when in use. Selectable IF bandwidths, selectable IF AGC/Manual Gain controls, Squelch and a BFO with variable Pitch Control are provided. The zero-center meter provides accurate tuning for FM signals while the right hand meter measures signal strength. The built-in speaker is a very small "communications quality" unit that is located behind the screened cover. A 600 ohm audio line is provided on the rear panel can provide excellent audio quality to a matched loud speaker. The "SPEAKER" switch is a factory modification that replaced a PHONE jack with a switch to silence the panel speaker. Many of the Nems-Clarke surveillance receivers were used to monitor Russian missile launches and analyze data transmissions along with any voice traffic. The 1306-B is a great performer with an impressive appearance.

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Rebuilding and Operating the AN/GRC-19
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     Rebuilding the Collins 51J Series Receivers
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