Western Historic Radio Museum
(U.S. Navy & U.S. Army Signal Corps) Military-Commercial Communications Equipment 1932 to 1959 photo: U.S. Navy Shipboard Radio Room showing WWII RAK/RAL & RAO/RBL receivers |
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WWII Communications Equipment
U.S. Navy
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Radiomarine Corporation of American (RCA) - RAZ-1 (AR-8503, AR-8503-P, RM-6) RAZ-1 was the Navy designation for a group of equipment consisting of a four tube longwave TRF receiver with regenerative detector, a matching one tube preselector and a one tube AC power supply - all built for shipboard use. The Navy number for the receiver is CRM-46092 but it was also known as the AR-8503 in commercial applications. The AR-8503 was in use as early as 1938, mainly in commercial shipboard radio rooms. The receiver circuit uses one RF amplifier, a regenerative detector and two stages of AF amplification. The one tube preselector is Navy number CRM-50092 or commercial number AR-8503-P and the AC power supply is Navy number CRM-20096 or commercial number RM-6. Tuning is from 15 KC to 600 KC in four bands. The Preselector was used to reduce regenerative signal radiation to the antenna in addition to increasing sensitivity and selectivity. The National Type "N" dials are 0-100 scaled with 180 deg. rotation and a calibration chart is included in the manual . The RAZ-1 could be operated from batteries if necessary. The receiver and preselector panels are beautiful machine-textured aluminum with a matte-chromium finish. The receiver case is copper-plated steel under the gray wrinkle finish and uses "shock-mount" feet that were screwed to the operating table, (the pre-selector and power supply were normally screwed directly to the operating table.) The Navy contract is dated December 2, 1941 - just five days before the attack on Pearl Harbor. The RAZ-1 equipment shown are all assigned identical serial numbers - SN:65. Performance of this operational RAZ-1 is incredible with an ability to extract weak signals out of the noise that is impressive. NBDs from all around North America, LW BC stations and Navy VLF RTTY stations from around the world are easily received. Output is to a set of Western Electric 509W earphones as recommended in the manual. (See our "Vintage Longwave Receivers" webpage for an in depth article about this receiver.) |
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Radio Corporation of America - DZ-2 RCA built this radio direction finding receiver for the Navy for use in search and navigation. The DZ-2 dates from 1939 though there were additional contracts during WWII. Using 8 tubes in a superhet circuit and tuning from 15 to 70 kc and from 100 to 1750 kc, the DZ-2 used a rotatable dual loop antenna and a fixed vertical antenna (usually a "T" wire from the cockpit to the tail) to determine "true" direction (called Uni-lateral Reception/Sense.) Non-directional and Bi-directional options were also provided. The dual loop antenna was mounted in an aerodynamic housing on the exterior of the fuselage and the remote drive control provided a readout of the loop's relative position for the radio operator. The DZ-2 also featured a BFO and Audio Filters. The receiver uses a cushioned shock mount. Power provided by battery and external dynamotor.
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Andrea Radio Corporation (for RCA) - RAK-7 (CND-46155) and RAL-7 (CND-46156) Designed for the Navy by RCA in 1935, the RAK and RAL receivers were used in various shipboard applications (also submarine) up through WWII. The two receivers were ruggedly built and reliable in their design simplicity. The RAK is a six tube TRF receiver with regenerative detector that covers 15 kc up to 600 kc in six tuning ranges. The RAL is also a six tube TRF receiver with regenerative detector but covers 300 kc up to 23 mc in nine tuning ranges. Tube line up is the same for both sets with four 6D6 tubes and two type 41 tubes. Both receivers use a dual dial readout (0/00 to 10/00) that must be correlated to a graph in the manual for tuned frequency. Each receiver has its own separate power supply, the CRV[CND]-20131, which provides power through a ten foot long cable that connects to a terminal strip inside the receiver. The power supply uses a 5Z3 rectifier, an 874 regulator tube and an optional 876 ballast tube that was supposed to be used when the AC line voltage was subject to fluctuations (supposedly that would cause instability in the RAL receiver at higher frequencies.) Meters on each receiver monitor the tube heater voltage (right) and the audio output (left.) The RAK receivers were intended for CW or MCW reception only as a low pass filter is permanently connected in the circuit to limit the upper audio response to about 1200 hz. The RAL has the option of allowing the low pass filter to be switched out of the circuit (switch in "BROAD" position) and can therefore can be used to receive voice transmissions along with CW and MCW signals. An elaborate audio AVC system is employed in both receivers to limit overloading and also to allow operation in heavy static conditions. An audio bandpass filter system is also employed in each receiver that allows the operator to select various audio frequency ranges via a front panel switch. The audio output Z is 600 ohms and is intended to drive earphones (but it will drive a 600 ohm Z speaker quite well.) The RAL and the RAK receivers were designed to work together through a separate control box (CRV[CND]-23073) that allowed the operator to monitor two frequencies simultaneously (each receiver tuned to different frequencies with the audio from each combined) and also to control power to each receiver. The RAK and RAL receivers are surprisingly good performers and interesting to operate. The RAK is a first class longwave receiver and can easily pick up NDBs from all over North America, WWVB or JJY (Japan's LF WWVB equivalent at 40KC) , along with LW BC stations and any of the VLF Navy RTTY stations worldwide. The RAL is also an excellent TRF receiver that will function quite well on the HF ham bands, even copying SSB stations with minimal drift (since there is no LO or BFO to worry about.) SW BC and AM BC can also be received with audio quality that is somewhat restricted but acceptable. The RAK-7 and RAL-7 pair shown in the photo are from 1945 and, like most RAK/RAL receivers, they were manufactured by Andrea Radio Corporation. Use of [ND] in Navy designation indicates Andrea manufacture and [RV] indicates RCA-Victor. (See our "Vintage Longwave Receivers" webpage for an in depth article about these receivers.) |
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Federal Telephone & Radio Corporation (for RCA) - RBA Series In the late thirties, it was becoming apparent that a replacement receiver was necessary for the aging RAK series of longwave receivers. The new design was going to blend the advantages of the TRF designs of the RAK but eliminate the regenerative detector in an effort to keep the radiation on the antenna to a low level that prevented enemy DF of the receiver location. Additionally, the low-level of radiation allowed the receiver to operate in the presence of other receiving and transmitting equipment and radar without interference. In order to allow demodulation of CW signals a "tracking" beat frequency oscillator (BFO) was incorporated into the design. Since the new receiver was not a superheterodyne, the BFO had to track the tuned frequency, providing a 1kc heterodyne which allowed CW to be readily copied. There were a couple of reasons for not designing the new LF receiver as a superheterodyne. First was to allow complete coverage of the tuning range of 15kc to 600kc and second was that fact that the conversion process in a superheterodyne creates a lot of internal noise in the receiver - not a real problem on HF or SW, but a serious determent to good LF performance. At $3000 each, the new RBA receiver was certainly expensive and a look inside the receiver reveals an incredible level of electro-mechanical design and construction. The tuning ranges from 15kc up to 600kc in four bands. The illuminated dial readout is direct in kilocycles along with a two-dial logging scale. The mechanics of the design allow for super-smooth operation of the tuning system. The Gain adjustment controls the sensitivity of the receiver and a gear-driven auxiliary gain control operates from the tuning dial and provides constant gain levels across the tuning range. Two meters are provided, one to monitor Output Level in db and one to monitor the B+ voltage. An Output Limiter is provided for noisy conditions or unexpected strong local signals with the Output Level adjustment setting the output limiter's maximum level. Two levels of selectivity are provided, Broad selectivity is limited to about a 1300kc audio roll-off via an internal LP filter and the Sharp position is provided by a 1kc bandpass filter for CW in noisy conditions or in cases of interference. Audio output is 600 ohms Z and is intended for earphones although the RBA will drive a matched loud speaker if necessary. The separate power supply, CRV-20130, provides the filament voltage and B+ requirements via an armored cable with heavy-duty connectors. The power supply will easily operate two receivers for emergency conditions and two separate connectors are provided. This is the same power supply used for the RBB and RBC receivers. The power supply has a cold-cathode regulator tube (OC3) and a HV rectifier (5U4.) The RBA uses eight tubes, three 6SK7 RF amplifiers, one 6J5 Triode Detector, one 6SK7 BFO, two 6SJ7 AF amplifiers and one 6K6 AF Output. Federal Telephone & Radio Corporation was owned by ITT and had grown out of the old Federal Telegraph Company that was originally located in Palo Alto, California. FTC's chief engineer was Frederick Kolster, sometimes credited inventor of the directional loop antenna. Lee DeForest was associated with the company at one time. During the mid-twenties, FTC built consumer radios under the "Kolster" brand name. Mackay Radio & Telegraph Company had close ties to FTC and all early Mackay maritime radio equipment was built by FTC. When Mackay was purchased by ITT in 1928, it was not very long before FTC also was added to the growing list of companies owned or controlled by ITT. The purchase took place around 1931 and at this time FTC moved to New Jersey. In New Jersey, FTC continued to build maritime radio equipment, usually for Mackay Radio. Around 1940, Federal Telegraph Company's name was changed to Federal Telephone & Radio Corporation. The early versions of the RBA receiver are identified as C(FT)-46154 (FT identifies Federal Tele.&Radio Corp. as the contractor) but later versions use CFT-46300 as the receiver identification. Shown in the photo is the CFT-46300 RBA-6 from 1945. This version is identical to the RBA-5 internally but the RBA-6 was rack mount only and was painted Navy gray rather than black wrinkle. The RBA-6 is an impressive performer with ample sensitivity, direct dial read-out with illumination and a tracking BFO rather than regenerative-autodyne detector. The tracking BFO actually works quite well for finding the carrier on NBDs. The dial accuracy is excellent and allows tuning NDBs by frequency rather than constantly referring to charts or graphs. The LP filter does limit the audio frequency response on BC stations but not to the point where the voice is incomprehensible. The OL works quite well at limiting the maximum output and not distorting the signal. The RBA is a first-class longwave receiver capable of receiving any of the LW signals found below 500kc. (See our "Vintage Longwave Receivers" webpage for an in depth article about this receiver.) |
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Radio Corporation of America - RBB (CRV-46147) and RBC (CRV-46148) In 1939, the Department of the Navy contracted with RCA to build the ultimate military communications receiver. The design was to replace the aging RAK/RAL regenerative receivers with new receivers of the same rugged construction but with modern performance capabilities. RCA utilized input from engineers from 17 other companies during the design phase of the new receivers. By 1940, the RBA, RBB and RBC were ready for production. The RBA was a TRF LW receiver that matched the RBB and RBC in size and power requirements (see previous receiver description above.) The RBB and RBC were true double preselection superheterodynes using 15 tubes plus a 991 neon bulb voltage limiter in the antenna input, a 6-8B Ballast tube for the Local Oscillator heater and the separate CRV-20130 power supply also used two tubes, a 5U4 rectifier and a VT-105 regulator - 19 tubes in all. The RBB receiver covers 500kc up to 4.0mc in four bands and the RBC covers 4.0mc to 27.0mc, also in four bands. The Local Oscillator's filament is operated from a 17vac tap on the power transformer through the 6-8B ballast tube also the LO's plate is operated from the regulated 105vdc supply. This design effort allowed the RBB/RBC receivers to exhibit very little drift. Three IF amplifier stages were used along with a three step selectivity control, a noise limiter control and a switchable audio bandpass filter. Since the AVC could not be on when receiving CW signals, an Output Limiter circuit could be switched in (CW-OL) to keep static bursts or unexpected strong signals from overloading the receiver or the operator's ears. An adjustable squelch control called a "Silencer" was also included. The construction of the receivers were as much as possible alike allowing many of the same parts to be used for each model. There are some tube and component differences in the preselector section of the RBB/RBC but the IF/AF section is identical for each receiver. Three panel meters provided monitoring of Signal Level in db, Audio Output in db and B+ in volts dc. The audio output was designed for 600 ohm Z earphones and up to 20 pairs could be connected in parallel, (who knows why but that's what the manual indicates.) Some of the later RBB/RBC receivers will have an additional 6AB7 tube installed along with a SO239 connector on the back of the receiver. This was an amplified IF output source generally used for a panadaptor. An internally mounted switch allowed the operator to select this IF amplifier output function if desired. The entire cabinet was mounted to the operating table by four shock mounts. Unlike the RAK/RAL receivers, the RBB/RBC had accurate direct frequency readout dials that were illuminated and there was also a "power on" pilot lamp. The CRV-20130 power supply was connected via a heavy-duty cable with huge nine-pin MIL connectors. Although the CRV-20130 power supply does provide two connectors to allow operation of two receivers with only one power supply, this was considered as "emergency only" operation. When operating two receivers from one power supply, both receivers will be "ON" regardless of which receiver's power switch is activated. The load of both receivers on one power supply drops the B+ voltage and the filament voltage by about 10 percent but any decrease in performance is only slightly noticeable. Super-smooth tuning with large, easy to read dials that are masked for band-in-use readout make the RBB/RBC series a pleasure to operate. The 600 ohm Z audio output will easily drive a matched loud speaker but the design intent was for earphone operation so don't expect thunderous volume. Sensitivity and selectivity are typical of the best designs of the day. The 1940 selling price (to the government) for these incredible receivers was $2400 each - a staggering amount of money. An internal examination shows why the price was so high. These rugged, over-built receivers had to withstand the constant mechanical vibration while at sea in addition to the mechanical shock of firing multiple 16" guns (along with firing all of the other artillery present on battleships) and also to hopefully be able to withstand the shock of a possible torpedo or bomb hit and still keep communications operating. Additionally, everything had to have maximum shielding to prevent stray emissions from the LO getting to the antenna and also to allow the RBB/RBC to operate in the presence of other receivers, transmitters and radar without interference. In many instances, the RBB/RBC receivers were so well-respected and their performance so good, they not replaced with more modern receivers until the mid-1960s - a testament to the RBB/RBC's magnificent design and construction. Shown in the photo above is the RBB-2 on the left and the RBC-3 on the right - both built by RCA. |
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National Company, Inc. & Wells-Gardner Co. - RAO Series National began supplying the U.S. Navy with their NC-100A direct dial readout, coil catacomb band switching receiver as early as 1938. Designated as RAO, the first version is similar to the standard NC-100AX receivers. When WWII began, the Navy wanted minimal radiation from the receiver's Local Oscillator on the antenna. This was primarily to allow the receiver to be used in the presence of other shipboard radio equipment without interference. Beginning with the numbered suffixes, e.g. RAO-1, RAO-2, etc., National added an extra RF Amplifer with an additional coil catacomb and tuning condenser housed in a bolt-on rear chassis and cover. The extra RF Amp provided the isolation necessary to keep the LO radiation on the antenna below the designated level of <400pW. The RAO circuit uses 11 tubes and tunes AM BC up to 30MC and also features a crystal filter, a tone control and a noise limiter. A 500 Z ohm audio output transformer was incorporated into the circuit as well, though this was standard procedure for Navy receivers and it is likely that the first versions of the RAO also had 500 Z ohm outputs. This was to assure that the B+ did not appear on the speaker terminals as was standard for the civilian National NC-100 series. RAO-2 and some RAO-6 receivers will have an ID from National of NC-120. Most WWII equipment was built under contract and not all RAOs were built by National. Wells-Gardner Company was the second contractor for the RAO series, building the RAO-3, 4 & 5. The Wells-Gardner versions were generally intended for shore stations and are not particularly "heavy-duty military-type" construction. National continued on with the Navy contracts building the RAO-6, 7 & 9 (the designation RAO-8 was not used.) These receivers were of robust construction and had increased shielding to further allow their use with other shipboard equipment without interference. The audio output Z was changed to 600 ohms with the later versions. The RAO-7 & 9 eliminated the S-meter in favor of panadaptor connections. The first RAO-6 receivers had S-meters but later production receivers did not. The later RAOs simplified the maintenance of the receiver by designing the chassis so that it was easily removable from the cabinet (handles were added to the receiver front panel to assist removal.) The cabinet itself was redesigned for better shielding and easier mechanical construction by making it a one piece unit and, though some later cabinets did have lids, most did not. The early RAOs used a separate shock mount system but the new cabinets mounted the shocks directly to the bottom of the cabinet further easing construction and maintenance. The RAO-7 & 9 receivers are physically larger than the earlier versions with full 19" rack width panels although the receivers are not designed for rack mounting. The earlier RAO versions are 17.5" wide, with an integral panel-cabinet-chassis construction that requires major disassembly to service or repair. The RAO receivers have impressive sensitivity and stability although the tuning rate is quite fast which was probably intentional for quick band scanning for signals. The fact that the later RAOs have provisions for panadaptor operation seems to confirm that they were used for surveillance rather than communications.
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National Company, Inc. - RBH Series The RBH was the Navy designation for the NC-156 receiver, a 10 tube superhet that covered 300kc to 1200kc and 1700kc to 17mc in five bands utilizing National's famous moving coil-catacomb bandswitching system. The receiver is a version of the NC-100AX that allowed continuous coverage of the 300kc to 500kc range by having the IF operate at 1500kc (which is why there is a gap in the tuning from 1200kc to 1700kc.) The receiver also features single preselection, two IF amplifiers, crystal filter, S-meter, BFO and tone control. The dial uses the articulated pointer that indicates band in use by its alignment with the proper tuning scale on the illuminated dial. The initial RBH receivers will have "NC-156" on the National Co. nameplate (part of the crystal filter panel.) The first RBH receivers date from around 1940, however the receiver required some modifications for use at sea during WWII and a series of RBH receivers followed. All of the RBH series with number suffixes, e.g. RBH-1, RBH-2, etc., have an additional stage of preselection added with a bolt-in chassis and cabinet to house the additional catacomb section for the coils and an addtional tuning condenser for tuning the stage. This addition was very similar to the RAO receiver change and was for the same purpose of reducing the LO radiation from the antenna (>400pW on the antenna.) The dial system changed on the later RBH receivers, eliminating the articulated pointer and painting the background white rather than silver. The last of the RBH receivers incorporated the same improved cabinet of the later RAO receivers. When operating an RBH today, strong AM-BC stations around 1500kc will resonate with the RBH's 1500kc IF amplifiers and can cause strong heterodynes when tuning in stations or, if the 1500kc AM-BC station is particularly strong, it may dominate the IF system of the RBH. A 1500kc wavetrap on the antenna lead-in will usually cure any serious problem. The early RBH receiver shown in the photo above unfortunately has had all of its Navy tags removed. Sometimes tag removal was a requirement for sales of surplus equipment. |
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National Company, Inc. - RBL Series National produced the RBL series of longwave TRF regenerative receivers for the Navy during WWII. The RBL uses a seven tube circuit covering 15 KC up to 600 KC in six bands. The tube line up consists of three cascaded 6SK7 RF amplifiers, a 6SG7 regenerative autodyne detector, a 6H6 audio limiter with a 6K6G audio output tube and the 5Y3G rectifier (5U4G in earlier RBLs.) Unlike the RAO that it resembles, the RBL receiver's bandswitch does not operate a moveable coil catacomb, instead an intricate set of gears simultaneously actuates two large ceramic bandswitches. Also unlike many of the WWII longwave receivers, the RBL series has direct frequency readout on the tuning dial. The receiver also included a selectable "broad" or "sharp" audio filter and an adjustable output limiter for operation during intense static conditions. The limiter control was very well designed and works wonders at reducing static bursts. Audio output is via the earphone jack on the front panel and is for 500-600 Z ohm 'phones. Heavy duty construction through-out and the entire receiver is fully shielded with a cabinet that is copper plated under the black wrinkle finish. The RBL-5 shown in the photo is from 1944 and its excellent original condition is matched by its first-rate performance. The RBL-5 is a great performer, capable of receiving NBDs from all over North America, world-wide LW BC, WWVB, JJY, Navy RTTY and almost all other types of signals in the LF spectrum. (See our "Vintage Longwave Receivers" webpage for an in depth article about this receiver.) |
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E. H. Scott Radio Laboratories, Inc. - SLR Series During WWII, Scott Radio Laboratories was contracted to design and build a type of military marine entertainment receiver that had very low Local Oscillator radiation or leakage to the antenna system. Scott advertising of the time indicated that the Navy was concerned with the possibility that enemy submarines could tune in a superheterodyne receiver LO signal and determine a ship's position with direction finding equipment. The Scott ads further stated that enemy DF equipment was sensitive enough to detect LO signals up to 100 miles away. While this all may have been theoretically true, the primary reason for the installation of low radiating receivers onboard ships is that any receiver has to operate in the presence of the several other receivers, transmitters and sometimes radar equipment that would also be in use on the ship. None of the receivers can cause interference with ship equipment and they must be able to perform their function without interference from other ship equipment. The "Scott Low Radiation" Receiver, or SLR, was built to operate in such a shipboard environment with no interference. It tuned the standard AM Broadcast band and two bandspreaded Shortwave bands. The SLR receivers were designed as a stand-alone receiver capable of high quality reception and wide range audio reproduction via its push-pull 6V6 output stage. The multi-tap output transformer allowed matching to virtually any impedance that might be encountered with 600 ohms being the most common. The receiver's output could be distributed throughout the ship via the 600 ohm line. Single preselection, two IF amplifers and a Noise Limiter were included. A BFO was also included in case the receiver had to double as a communications receiver. When in the C.W. position, the AVC is disabled and the Volume control actually controls the RF-IF gain so the signal to BFO injection ratio is correct. A cathode-ray "tuning eye" tube was also included in the SLR version. Scott also built the RBO receiver, a similar looking set but without the push-pull audio and BFO. Parallel rectifiers are used in the RBO and sometimes the receiver is seen with a drop-down dial cover - a hinged metal piece that can be raised up to entirely cover the illuminated dial. The RBO generally was used with the ship's 600 ohm line. Both receivers were installed in a very large metal cabinet that was shock-mounted to a substantial base mount. Many different versions of these "entertainment" or so called "Morale Radio" receivers were built. The receivers were installed not only on U.S. Navy ships but also merchant ships, tankers, transports and other types of American vessels. |
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The Crosley Corporation - REO Crosley seemed to have most of the WWII contracts for the smaller "Morale Radios" destined for shore use. Though the Scott SLRs could and were used aboard ships, the smaller radios were generally designed to be less expensive and this usually resulted in excessive LO radiation which prohibited their use aboard ship. Though some of the more elaborate "Morale Radios" for shore use were sometimes found in metal cabinets, the REO is housed in a wooden cabinet that is painted Navy gray. This simple radio covers AM BC only. The controls are left to right, Volume, On/Off and Tuning. The Navy wanted to be sure that every user was aware that the REO was strictly "land use only" and provided a large red warning tag stating so ("Unsafe Radiation Limits" refers to the radio's Local Oscillator signal radiation from the antenna and elsewhere in the circuit since the cabinet provides no shielding.) |
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WWII U. S. Navy Contractor Designators During WWII most U.S. Navy equipment built for the war effort was assembled or constructed by contactors. Many times the items built would be a specific model of a particular company and would have exactly the same company parts and same assembly techniques but the item was assembled by a contactor company. The contactor-built equipment had to meet the same specifications and therefore most of the time the equipment performs exactly the same as another example built by another contactor. Each contactor had a specific letter identification that was incorporated into the specific model number. So, if a piece of Navy radio equipment is ID'd as CFT-43600, then that piece of equipment was built by Federal Telephone & Radio Corporation. To the right is a list of designators used for some of the various contactor companies during WWII. |
CAY - Westinghouse
CND - Andrea Radio Corp. CCT - Stromberg-Carlson CPN - Panoramic Corp. CFT - Federal Telephone & Radio Corp. CKR - KEN-RAD CRV - RCA-Victor CME - Radio Manufacturing Engineers, Inc. CWQ - Wells-Gardner Co. CNA - National Co. Inc. CZC - Scott Radio Laboratories, Inc. |
U.S. Army Signal Corps
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National Company, Inc. - NC-100ASD National introduced a well designed, direct-reading dial for their NC-100 series receivers in 1938. The "A" version dial had a mechanically articulated dial pointer that indicated the band in use when switching ranges and also added an S-meter as standard equipment. All of the other NC-100 features were retained, including the moving coil catacomb bandswitching, P-P audio, tone control, noise limiter and an optional crystal filter which was indicated by an "X" in the model designation. Around 1938, the Signal Corps wanted the NC-100A with special frequency coverage that included a longwave band. This was provided (200kc to 400kc) but the AM BC band coverage was dropped. The upper bands cover 1.2Mc to 30Mc. Also, the P/P audio was changed to a single-ended 6V6. The Signal Corps also didn't want to use an electrodynamic speaker so a 500 Z ohm output transformer was installed designed to drive a matching 500 Z ohm PM speaker. The designation for this model was NC-100ASD (shown in photo.) The Navy also wanted their own version of the NC-100A - it was designated as RAO - more details above in Navy equipment. |
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Hammarlund Mfg. Co., Inc. - WWII Military Super-Pro 200 Series The military had several different Super-Pro versions built during WWII. Most versions were nearly identical to their civilian counterparts in the SP-200 line. As with most military contracts at that time, other companies besides Hammarlund built the military Super-Pros (Howard Radio being the most commonly seen.) The most popular military versions were BC-779(civilian LX) covering 100 to 400kc and 2.5 to 20mc, BC-1004(civilian X) covering .54 to 20mc and BC-794(civilian SX) covering 1.2 to 40mc. There were other assigned model numbers also, probably depending on the end user of the particular contract. Also, a suffix was sometimes added to the BC designation indicating the type of power supply that went with each receiver. Hammarlund's advertising implied that many Super-Pro receivers were also used by our WWII Allies. Internally, there are only minor changes made to the civilian Super-Pro for military use. Many of the capacitors are combined into "bath-tub" type units that mount on the side wall of the chassis. Also, the wiring harness uses stranded wire and sometimes the solder joints are MFP'd. All of the WWII military Super-Pros use a steel front panel that is copper plated under whatever type of paint was used. Generally, the steel panels were painted with a smooth finish and the stamped nomenclature was white filled. Panel colors range from black or gray to shades of green-gray or blue-gray. There were several variations in the construction of the power supply also with most military versions using heavy-duty, over-size transformers and chokes along with oil-filled filter condensers. Some power supplies had dual primary or multiple tapped primary power transformers to allow operation on 230/115vac or a variety of ac voltages around 230/115vac. Designations are usually RA-74, RA-84 or RA-94. The military Super-Pro receivers are great performers with fantastic audio, although most are rack-mount versions which is a configuration not usually favored by collectors. Additionally, many of the military models are in deplorable condition today due their lack of appeal to hams during the last several decades. The receivers not only require the normal electronic restoration but a serious cosmetic restoration, too. Only recently has the WWII Super Pro found an appreciative group of hams and collectors that find the build quality and superior performance to be unmatched by most of its contemporaries. Shown is a military ASP-1004 (same as BC-1004) - probably destined for Allied use (ASP=Allied Super Pro?,) with an original light greenish-gray panel, from the later part of WWII. Note the eight holes around the outer edge of the panel - these are on all military Super-Pro receivers and normally were there for mounting the chassis dust cover. However, sometimes these receivers were installed in a military desk-top cabinet designated CH-104-A with the dust cover removed and screws and nuts installed in these holes. Russia and Australia both built Super-Pro "knock-offs" during WWII, the KV-M from Russia and the AMR-200 built by Eclipse Radio in Australia. See "The Incredible Pre-War Super-Pro" web article for more details on military Super-Pro receivers, navigation link below. |
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Radio Corporation of America - BC-348 Series - Various Manufacturers The BC-348 Aircraft Receiver was designed by RCA in the late thirties. It operates on 24-28vdc with the high voltage (~+220vdc) provided by an internal dynamotor. Many thousands were built during WWII by many different contractors building many different versions within that time period. The circuit used eight tubes with the heaters originally wired in dual-series for 24vdc operation (each of four 6 volt tube heaters in series would operate on 24vdc.) The early circuit provided two RF amplifiers, a Mixer, a Local Oscillator, an IF amplifier stage, a combination 2nd IF amp and BFO, a combination 3rd IF amp and Detector/AVC followed by a type 41 audio output stage (this was changed to a 6K6 in some versions.) Some versions will have a 991 neon lamp acting as a regulator on the local oscillator and some versions provide an antenna trim control. The later circuit used two RF amplifiers, a converter stage, three IF amplifiers, a duplex diode/triode provided Detector, AVC and BFO functions and a 6K6 provided the audio output. The audio output impedance was internally selectable at "low Z" which was around 300 Z ohms or "high Z" which was around 4000 Z ohms (on later versions.) Some BC-348s will have a decal on the front panel indicating if the "low Z" was optioned. A selectable crystal filter was also included in the circuit. The dual dial lamps were adjustable for brightness and were wired in series through a potentiometer and fixed resistor. Frequency coverage was from 200-500kc (not on the B version) and 1.5-18mc. When the receiver was installed on its FT-154 shock mount and installed in the aircraft, an eight pin Jones plug mated with a receptacle and cable that exited from the rear of the mount containing the 28vdc input, the remote stand-by relay function and an audio output line. The BC-348 was generally interconnected with the transmitter (usually a BC-375) to control boxes allowing the transmitter's control relay to provide antenna switching, receiver stand-by and providing side tone monitoring which allowed for full "break-in" keying. Since there are so many variations, military collectors have generally divided the BC-348 into two groups, early types (B, H, K, L, O, P & R) with grid cap type tubes and the later versions (J, N & Q) with single-ended tubes. Several of the earlier versions were rebuilt into later configurations, especially to add the 200-500kc band. The conversion of the "B" into an "R" is typical of the process. Many different contractors built BC-348s but Wells-Gardner Co. probably built the greatest quantity of receivers and is the most commonly seen manufacturer. The BC-348 became available as surplus in the 1950s allowing hams the ability to purchase a great performing receiver at a reasonable price - NOS and still in the crate for about $75. The down side is that today it is almost impossible to find a BC-348 that hasn't been modified. Typically, the dynamotor will have been removed and an AC power supply added. This mod was fairly simple and usually didn't compromise the receiver's performance (other than adding some hum to the audio output if the power supply wasn't well-filtered.) Many other dubious mods were published in various surplus conversion books of the day that did compromise the BC-348's performance. Additionally, many hams would drill the case with lots of .25" holes thinking the receiver needed extra cooling. Originally, the BC-348 operated at altitudes up to 25,000 feet where the temperature inside the aircraft was below zero - cooling the receiver was not a problem. But even on the ground in other applications, the BC-348 didn't run hot and adding ventilation holes will only ruin the cabinet. A great performing receiver when conservatively modified (AC PS only) and accurately aligned. Shown above is a 1943 Wells-Gardner version BC-348-Q. Other variations include, the BC-224, which was a 12vdc version used for earlier aircraft electrical systems. Its external appearance is identical to the BC-348. See next listing for the actual use of the BC-348-Q receiver in a working environment... |
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SCR-287 - B-17 Bomber Radio Station BC-375-E - General Electric Corp. & BC-348-Q - Wells-Gardner Co. The SCR-287 comprised a complete liaison radio station installed onboard various bombers and transports during WWII. The transmitter used was the BC-375 along with the BC-348 as a receiver. Though the BC-375 was designed in the early thirties and built from the mid-thirties on up to mid-WWII, it found a long-term usage with the Signal Corps due to its ease of operation and reliability. The BC-375 uses four VT-4-C triode tubes (type 211) and a single VT-25 (10Y) triode with one VT-4 used as the Master Oscillator, another VT-4 as the Power Amplifier and two VT-4 tubes for the P/P Modulator. The VT-25 serves as the speech amplifier in the Voice mode (AM,) as a 1000hz oscillator in the Tone mode (MCW) and as a sidetone oscillator in the CW mode. Power is provided by the aircraft battery/charger system (24 to 28vdc) and by a high voltage (+1000vdc) dynamotor (PE-73.) The transmitter frequency range is determined by which of the seven Tuning Units is installed in the transmitter. The coils and condensers and connections for the MO and PA are contained in each TU. The range of frequencies is from 200kc to 500kc and from 1500kc up to 12500kc using the various TUs. The controls aligned vertically on the right side of the transmitter make up the wide range antenna coupler for the transmitter. The BC-306-A located to the right of the BC-375 is the LF Antenna Tuner allowing further extension of antenna matching ability below 800kc using the typical trailing wire antenna. Power output is between 50 and 90 watts. The BC-375 provides full break-in keying by allowing the elaborate internal antenna relay to control the receiver antenna and the receiver standby circuit. Additionally, external inputs via the PL-64 cable allow remote microphone and key operation along with remote power control. The aircraft was usually set-up to allow the pilot to also access the transmitter/receiver for various reasons. The other components shown are the BC-348-Q receiver which does run on its original dynamotor from the battery supply, the Lionel J-47 telegraph key and the Shure Bros. carbon microphone, the T-17. The speaker is an LS-3, although these were never used in the SCR-287 or onboard the aircraft. Four BC-375 Tuning Units are mounted in their CS-48 containers on the wall. The console features a fold-down desk, a sound-proof (almost) compartment for the PE-73 dynamotor and a bottom shelf for the four storage batteries (four 12v batteries in series-parallel = 24vdc.) The panel to the left of the BC-348 has all of the remote connections for receiver audio output, receiver stand-by, xmtr CW sidetone select, xmtr microphone input and xmtr key input. After WWII, the BC-375 was available surplus for about $15. The various TUs were also available at "give-away" prices. This lead to many hams buying the BC-375 for an economical way to get "on the air." Unfortunately, most hams tried to rebuild the BC-375 into something that it was NEVER intended to be - a ham transmitter. The end result was a bad reputation that the BC-375 was unstable, sounded awful, created horrible TVI and was only useful as a resource for parts to build other ham projects. Most of the BC-375's bad rap came from hams expecting a military aircraft transmitter to work like a ham transmitter, so improperly designed, inadequate power supplies and modifications to the original design concept were considered the standard solution. Though TVI was a problem in the fifties, today's strong TV cable and satellite dish signals are not affected by the BC-375 operation. The transmitter's stability depends on the frequency of operation and most problems arise as the frequency of operation is pushed above 4.0 MC. For more details on successful operation of the BC-375-E "on the air" go to this short article - Using the BC-375-E Today |
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U.S. Army Signal Corps - BC-312, BC-314, BC-342, BC-344 Series - Various Manufacturers The BC-342 is part of a series of receivers that includes the BC-312, BC-314, BC-342 and the BC344 receivers. These are stoutly built receivers that make use of extensive shielding utilizing steel sheet metal rather than aluminum (although the earliest versions do use mostly aluminum construction.) The circuit is a nine-tube superheterodyne (ten tubes in the BC-342 and BC-344 which includes the 5W4 rectifier tube.) Two 6K7 RF amplifiers are used along with a separate 6C5 Local Oscillator and 6L7 Mixer tube. Two 6K7 IF amplifiers, a 6C5 BFO, a 6R7 duplex-diode triode for the Det/AVC/1st AF function and a 6F6 audio output tube complete the tube line up. Frequency coverage is from 1500kc to 18000kc in six tuning ranges for the BC-312 and BC-342. The BC-314 and BC-344 are medium wave receivers and cover 150kc to 1500kc in four tuning ranges. The BC-312 and BC-314 are operated on 12-14vdc (BC-312-NX version 24-28vdc op) and were intended for vehicular use, which could include trucks, cars, jeeps or tanks. The BC-342 and BC-344 included the RA-20 AC power pack allowing the receivers to operate on 110-120vac with the intention of use within a building installation or mobile use with AC generator. The huge connector protruding out of the front panel allows power input on DC versions or filament voltage access on AC models, telegraph key, PTT and microphone routing, stand-by in DC versions, audio outputs and antenna relay function for interfacing with transmitters and other equipment. There are several variations for each model in the series with some receivers having Crystal Filters installed, some have selectable audio output 250 ohms Z or 4K ohms Z, some also allow access to the 1st AF output for earphone operation along with many other subtle variations depending on when the receiver was built. The BC-342 series of receivers were used extensively in ground applications from just before WWII up into the 1950s. If you are planning to restore one of the BC-312/342 family of receivers, be aware that the mechanical design of the receiver does not consider ease of maintenance beyond changing tubes and routine alignment. The receiver is difficult to disassemble, requiring the unsoldering of several connections just to remove the front panel. Dismounting any of the assemblies is arduous. There are many different length screws and standoffs that have specific locations so care must be observed during disassembly to keep everything identified for proper reassembly. It is routine to have to dismount several parts or assemblies just to access other parts for removal. Any serious restoration work is sure to result in several large piles of sorted screws and other parts before reassembly can begin. The laborious restoration work will be rewarded however, as the BC-312/314/342/344 receivers are excellent performers with great sensitivity and plenty of audio when driving a matched speaker. Shown in the photo is a Farnsworth-built BC-342-N. This is an early version of the "N" with the wire dial fiducial, non-selectable audio output Z (fixed 4K ohms) and the typical Signal Corps hand-written upgrade nomenclature above the ID tag. |
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The Hallicrafters, Inc. - R-44/ARR-5 This VHF receiver provided airborne search capabilities and was designed to find enemy radar or other signals. The R-44 is a 14 tube superhet tuning from 27.8 to 143 Mc in three bands and receiving AM, CW or FM signals. Motor-drive tuning provided a "search" scanning mode. Outputs for visual indicators were also provided. A special "stub" antenna was used (AT-38) and a separate power pack (PP-32) provided the power for the receiver (and added three more tubes, although these were to provide B+ for three individual receivers.) Sometimes this receiver is called the "Airborne S-36" based on its similarity to Hallicrafters' VHF base receiver, the S-36. |
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The Hallicrafters, Inc. - R-45/ARR-7 Like the receiver above, the R-45 was an airborne search and surveillance MF and HF (.55 to 43mc) receiver that was primarily used for visual analysis of enemy radar and other types of signals. The Panadaptor and Video Outputs were designed to feed into specific airborne versions of typical panoramic adapters and to oscilloscopes. The oscilloscopes sometimes had built-in oscillators to create lissajous patterns for audio analysis of incoming signals (Video output is from the 6V6 audio stage of the receiver.) The panoramic adapters monitored the output of the Mixer stage of the receiver and provided a visual representation of the spectrum surrounding the receiver's IF passband. This allowed the operator to "see" signals that were outside the receiver's passband and couldn't be heard - but they could be seen on the panadapter, allowing the operator to tune to the signal for investigation. The R-45's circuit is very similar to the SX-28A, although "stripped down" to the essentials and considerably lightened for aircraft use. 12 tubes are used (not including the rectifier that is located in the PP-32 power pack.) Some of the similarities to the SX-28A are the use of the same Micro-set coils in the front end, six selectivity steps with three utilizing the crystal filter. The differences from the SX-28A are the Noise Limiter which is just a clipper circuit, use of a VR tube, no bandspread and the "militarily basic" audio output system which is just a capacitive coupling from the 6V6 plate to drive the headphones. Up to three combinations of the R-44 or the R-45 receivers could be powered by the PP-32 power pack that provided the heater voltage (6.3vac) and the B+ (+275vdc) but the scanning motor drive was powered by the aircraft battery system (+24vdc.) Additionally, the PP-32 operated off of 115vac 400 cycle provided by the aircraft's ac system. |
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The Hallicrafters, Inc. - Army-Navy AN/GRR-2 Most of the SX-28 and SX-28A receivers built for the war effort were standard Hallicrafters' production. In 1943, some SX-28s were built to a "heavy-duty" configuration that included a potted power transformer, dipped filter choke and audio output transformer and the return to the gear-driven bandspread tuning. These "heavy-duty" SX-28 receivers went to the Navy and the Signal Corps. Around April 1944, the SX-28A was introduced. It featured a series of improvements that had been incorporated into the very last of the SX-28 production. The major exception to these improvements was the High-Q Micro-set coils used in the receiver's new front-end and the installation of these coils warranted the designation change to "SX-28A." The U.S. Army Signal Corps and the U.S. Navy, wanted the SX-28A in the special "heavy-duty" build configuration and only these SX-28A receivers were given the designation of AN/GRR-2. The GRR-2 receivers are quite different from the standard SX-28A. The main differences are - the GRR-2 uses the same potted power transformer built by General Transformer Company, Korite dipped filter choke and audio output transformer and the gear-driven bandspread tuning system. This gear-driven bandspread been used in the earliest versions of the SX-28 receiver (the gear drive had been replaced with a dial string drive in mid-1941 SX-28 production.) The GRR-2 also has wax impregnated IF transformers and bandswitches, MFP fungicide coating on the solder joints and special heavy duty nylon insulated stranded hook-up wire in the harnesses. Additionally, the GRR-2 front panel was copper plated under the dark gray paint and the heavy-duty ball-end toggle switches have bakelite housings. The S-meter is a special unit that uses a bakelite case and is mounted using a special yoke system that mounts to the front panel with only two screws. All GRR-2 receivers were originally configured as rack mounted receivers and utilize a dust cover with hinged lid that provides ample protection whether the receiver is actually rack mounted or used as a table top receiver. The Signal Corps had its own manual for this receiver - TM-11-874 - with more detailed information than the standard SX-28A manual. The Signal Corps AN/GRR-2 shown is serial number HA-2703 and the fungicide dating is May 27, 1944. Only a few hundred AN/GRR-2 were produced. |
Military-Commercial Communications Receivers - 1932 to 1959
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Mackay Radio & Telegraph Co. - Type
105-A Mackay Radio & Telegraph Company was founded by Clarence Mackay, son of John W. Mackay, one of the "Big Four of the Comstock" fame here in Virginia City, Nevada. John Mackay initially made his fortune in Comstock silver but he later (1883) moved into telegraphic communications. Mackay, along with J. Gordon Bennett Jr., formed several telegraph communications companies to compete with Jay Gould's Western Union. Postal Telegraph Company (1886) was the best known, along with Commercial Cable Company (1884). Eventually, these companies, along with other Mackay-Bennett telegraph companies, had transoceanic cables across both major oceans. When John Mackay died in 1902, Clarence inherited the businesses. Clarence Mackay saw to the completion of the transpacific cable in 1904. Radio was added to the business end of things in 1925 to provide "radiogram" service to every area of the world. Mackay Radio was mainly interested in maritime communications which went along with the maritime radio-telegraph business. By 1928, ITT had merged with most of Mackay's business interests but the Mackay name continued on for several decades. Today, Mackay Communications is still doing business, located in North Carolina. Federal Telegraph Company started out in Palo Alto, California mainly dealing in arc transmitters. At one time, Lee DeForest worked for the company but Frederick Kolster was the head engineer for most of FTC's history. FTC bought Brandes and created a division called Kolster Radio Company for selling consumer radios in the mid-twenties. FTC became involved with Mackay Radio in 1926 when Mackay bought a radio station that had belonged to FTC. When Mackay sold his interests to ITT, then Federal Telegraph was contracted to do most of the Mackay Radio work. Federal Telegraph moved to New Jersey in 1931 when it was purchased by ITT. For awhile ITT tried the consumer radio market with Kolster International but it was a short-lived venture. The name of Federal Telegraph Co. was changed to Federal 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.)
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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 1941 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 at Bletchley Park, England for successful intercept work during WWII (along with National HRO receivers.) 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.
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. |
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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.) |
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Collins Radio Co. - 51J Series Introduced in 1949, the 51J series was developed as a general coverage receiver primarily for military, commercial or individual use providing accurate frequency readout and great stability. The receiver utilized a permeability tuned double conversion circuit with the 70E-7 PTO in a dual tuned IF system and a multiple frequency crystal oscillator to cover .5mc to 30.5mc in thirty (1mc wide) bands. Dial accuracy is maintained at 1.0kc throughout the tuning ranges by limiting the coverage of each band to 1.0mc. Band 1 actually is triple conversion but only to allow coverage of the AM BC band. Bands 2 and 3 are single conversion while all of the remaining bands are double conversion. 16 tubes are used in the 51J-1 and J-2. The ham bands are high-lighted in green on the megacycle drum dial but, at nearly $900, not many hams could afford a 51J as their station receiver. Early versions have a metal dial bezel, the Collins' "winged emblem" and an illuminated S-meter. Audio response is restricted at 200 to 2500Hz and is definitely not high fidelity, usually sounding somewhat "muffled" when receiving AM voice signals. In 1952, the 51J-3 was introduced, featuring an 18 tube circuit (adding a voltage regulator and vfo buffer,) a new version of the PTO (70E-15) and eliminating the 300 ohm Z antenna input (by removing the primary winding on the antenna coils) and redesigning the antenna input to a more flexible design with antenna trim control. This revision was at the request of the Signal Corps, who wanted to use the 51J receiver for their teletype installations but found the fixed 300 ohm Z antenna input requirements difficult to work with as most of their installations used Lo-Z vertical whip antennas. The military had their version of the 51J-3 designated as the R-388 and it was built from 1952 through about 1955. In 1955, the 51J-4, with 19 tubes and mechanical filters, became available and was offered up to about 1964. The 51J-4 and R-388 are the ultimate evolution of the design but the earlier 51J-1 and J-2s have their own appeal and top-notch reception for most modes of transmission. Shown is an early 51J-2 from 1950. If you are working on a 51J-2 receiver be aware that the 1950 version of the 51J-2 manual is fraught with errors, especially in the receiver alignment section and the component identification layouts. As to the 51J/R-388 performance overall, most of the 51J/R-388 receivers were used for data reception such as RTTY where the severe audio limitations made sense. For AM BC reception and SW BC reception the receivers are somewhat disappointing in their limited audio reproduction. There are also issues with the AVC circuit which never seems to function very well. Dial accuracy and stability - both necessary for RTTY work - were the 51J selling points to the Signal Corps and still are the 51J's primary attributes today. |
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Hammarlund Manufacturing Co., Inc. - SP-600 Series Introduced in 1950 and selling for nearly $1000 at that time, the SP-600 was intended for the military and commercial user market. It was a very popular receiver and many thousands were built, especially for military applications. Though most versions were built throughout the 1950s, the SP-600 continued to be produced in smaller numbers up into the early 1970s. The standard SP-600 tunes from .54 to 54MC in six bands. A "J" suffix indicates JAN parts were used in the construction and an "X" suffix indicates a switchable crystal LO. Hammarlund also offered a "JL" version with 100-400KC substituted for the .54-1.35MC band and a "VLF" version that covered 10-540KC. Hammarlund made over 40 variations that were assigned a numerical suffix which identified the particular circuit, mechanical changes or sometimes the end-user. The last in the "time-line" was the model variation SP-600 JX-21A from 1969-1972 which utilized a product detector circuit, two additional tubes and some other changes to make it "compatible" with SSB operations. Most versions use a 20 tube double conversion superheterodyne circuit with a rotating turret bandswitch. The receivers also feature enormous proportions, robust construction and oversize controls - along with a super-smooth tuning system that only adds to the enjoyment of operating these fine receivers. Double conversion is switched in above 7.4MC and uses a crystal controlled conversion oscillator. Though the SP-600 has two dials, it has no bandspread - the right side dial is a logging scale allowing precise retuning of desired stations. On the left is the main tuning dial and the mechanically articulated dial pointer that indicates which tuning scale is in use (along with the small window between the dials that shows which tuning range is selected.) The tuning arrangement was an up-dated version of the "Continuous Bandspread" system introduced in RCA's AR-88 series receivers in the 1940s. The frequency readout accuracy is vague which is why a precise logging scale system is incorporated into the SP-600 design. The S-meter is not illuminated and a switch is provided to indicate either carrier level or audio output. Most (but not all) SP-600 model numbers usually will have a suffix with "J" or "JX" followed by a numeral. As mentioned above, suffix "J" indicated that, as much as possible, military level components and construction were used. Suffix "X" indicated that a switchable six-position, fixed-frequency crystal-controlled oscillator was installed that allowed the user to install HC-6/U type crystals for specific desired LO frequencies. The user could switch to any of the crystal LO frequencies for increased stability for that particular frequency - however, the receiver still has to be "tuned" to the desired frequency for the RF and Mixer stages to be in tune. Many SP-600 receivers were set-up for diversity operation and the standard diversity model was the JX-17 version. This version was produced in large numbers and can be easily spotted by observing that it has two extra controls and uses three red colored knobs. The SP-600 Audio output is about 2 watts from a single 6V6 using a balanced split-winding audio output transformer for 600 ohms Z. The audio quality from a rebuilt SP-600 is impressive (although the lower end audio is rolled off at 125Hz 3db down resulting in an apparent lack of bass response.) 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.
It is interesting to note that Hammarlund did not refer to the SP-600 as a "Super-Pro" receiver in their manuals and only occasionally is its "Super-Pro" lineage mentioned in Hammarlund advertising. The 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. This particular JX-21 has been totally rebuilt and the front panel painted Hammarlund Green (a color used on WWII Super-Pro receivers.) The JX-21 is installed in an original SP-600 cabinet. 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 pleasant sounding audio. If you're looking for "to the kilocycle" accuracy though, maybe you'd be happier with something by Collins,...like the following receivers. |
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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.
The R-390 and R-390A receivers have provided reliable communications under adverse conditions for years and even though the designs are over 50 years old, they are still one of the best tube-type receivers around. Many R-390 and R-390A receivers are still being used today, some in professional applications, but also for serious SWLing and, of course, in vintage ham stations around the world. Many AM operators prefer the R-390 version for its better over-all sound quality when listening to SWBC or AM stations in general, however one must consider the maintenance challenges when selecting the R-390 for a station receiver. Nowadays, many R-390 and R-390A receivers are being used in "as purchased" condition - that is, the receiver has not been thoroughly serviced and properly aligned (or is it "alined?") The performance of a fully functional, freshly serviced and recently aligned R-390/390A is incredible. The header photo shows our 1951 Collins R-390 housed in an original 1955 CY-979/URR aluminum table cabinet. The inset photo shows our 1955 contract (built in 1956) Collins R-390A. Who knows what the "37.4" stencil means? (I don't.)
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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. |
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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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Technical Materiel Corporation - GPR-90, R-825/URR Technical Materiel Corporation, or TMC, was founded in 1934 by Ray DePasquale and, by the early 1950s, had become a major supplier of receivers, transmitters and accessories for the military and for commercial users. TMC introduced the GPR-90 communications receiver in 1955 with a selling price of $395. The circuit used 15 tubes and provided several unusual features, such as a three-position audio filter with adjustable audio bandwidth (on 1200~ position,) the multi-impedance output taps on the audio output transformer (4, 8, 16 and 500 ohms Z) and a great performing, wide range crystal filter. The circuit also featured two RF amplifiers on bands 3, 4, 5 and 6 (3.3mc - 31.5mc) along with double conversion on bands 4, 5 and 6 (5.4mc -31.5mc.) The first RF amplifier is a grounded-grid configuration with a wide-band input transformer to allow both 75 ohm Z and 300 ohm Z input impedances over the entire tuning range of the receiver. The cabinet was painted an unusual dark blue wrinkle finish and had an easily removable top lid for access to the top of the chassis. After the first year of manufacture, a 100kc crystal calibrator was installed and the selling price increased to $495. The military used the GPR-90 and identified it as the R-825/URR. The GPR-90's performance has been a source of controversy for many years and it is common to find diverse reviews, some "panning" the receiver as "lacking sensitivity" or "not up to TMC standards" while others praise its reliability, great audio quality, impressive styling and overall competitive performance. When a GPR-90 has been well-cared for and it is in good operating condition with a recent alignment, it is a superb performer with fabulous audio reproduction, highly adjustable selectivity and tremendous sensitivity. The Crystal Filter in the GPR-90 is the best performing crystal filter in any communications receiver. TMC addressed the issue of "not to the kilocycle accurate" dial readout in a 1956 Sales Service Information sheet (SUP-1 GPR 9-56) that stated, "People who require frequency meters should buy frequency meters - not make them double as communications receivers." Obviously a humorous "slam" against the competition (Collins.) The GPR-90 shown is an early version (without the crystal calibrator) from 1955. The GPR-90 was built from 1955 up to 1962. TMC is still in business today and, although the company is very small, it is run by Neil DePasquale, son of the original founder. For some reason, many of the GPR-90 critics want to compare this $400-$500 receiver to the $2200 (1967 price) R-390A receiver. The design concept of these two receivers couldn't be more diverse and a comparison simply isn't valid (other than to illustrate what can be designed and built when the end-cost is not an issue.) A more comparable receiver would be the Hammarlund HQ-180 - a receiver that was similar in design, construction and performance. In fact, the GPR-90 even bares a physical resemblance to some of the Hammarlund "HQ" receivers. |
References:
1. "Communications Receivers - The Vacuum Tube Era, 1932-1981" by Raymond S. Moore - Undoubtedly the best reference book on tube-type superheterodyne communications receivers. History of receivers and the companies along with circuit description and photos of each receiver. Four editions have been printed.
2. "Shortwave Receivers Past & Present - Communications Receivers 1942-1997" by Fred Osterman - Excellent reference book on later communications receivers. Includes many foreign makes. Circuit descriptions, photos, prices.
3. QST, Radio News and Shortwave Craft magazines from 1928 up to 1948 - These vintage magazines are excellent sources for contemporary reviews of equipment and pre-production articles by the designers. Advertisments are invaluable for dating and development of the model line.
4. Operator's Instructions, Factory Manuals, Rider's Troubleshooting Manuals - Original manuals are excellent sources for circuit descriptions, design intentions and performance expectations. Many times the same information is included in the appropriate Rider's Troubleshooting Manual.
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CFT-46300,
RBA-6 from 1945
1944
- National Co. - RAO-7, sn:10
RBL-5
SLR-F
Receiver
ASP-1004 Receiver
1943 -
Wells-Gardner - BC-348-Q
1943 -
Farnsworth BC-342-N
AR-88D
ca.1944
1950
Collins 51J-2
1953
Hammarlund SP-600-25C
1961 Capehart R-390A 
