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Radio Receiver BC-348

Developed by the U.S. Signal Corps Laboratories in Fort Monmouth, produced by various U.S. manufacturers under so-called contracts.

The BC-348 receiver was built under licence by various manufacturers for the U.S. Signal Corps during the Second World War and was one of the most popular receivers used in American bombers during the Second World War. In Switzerland, it was used in the H-Station resp. SE-018/m of the Swiss Air Force.

The original technical design of the receiver, which was initially fitted with grid cap tubes („GCT „), was simplified during the war years and tubes without the typical top connections („SET „, single-ended tubes) were used. Visually, the variants are very similar, but technically the receivers are completely different in design, and different tubes with different functions are used.

The receivers, which were built in big numbers, were often modified by radio amateurs in the post-war period and are becoming increasingly rare in their original condition, at least in the USA.

Radio Receiver BC-348

Technical data

Power supply

  • Converter operation: 28 V direct current (aircraft - on-board voltage) with rotary converter DM-28
  • Mains operation: via mains power supply NG-V with 110 / 125 / 145 / 220 / 250 V alternating current

Dimensions

  • 460 x 230 x 220 mm, 20 kg

Accessories

  • Mounting frame FT-154-(P)

Radio Receiver BC-348

Operation

The BC-348 receiver has seen use in the Swiss Army as part of the ground radio station H-Station (SE-018) or SCR-287 of the Swiss Air Force.

The BC-348 receiver has a sturdy, surprisingly light black-painted aluminium cabinet, the weight and the 28 V direct current power supply which was fed from the aircraft's on-board power, indicate that the set was developed as an on-board aircraft radio. The plate voltage is generated by a „dynamotor“ (a rotary converter),

The frequency dial is located in the centre of the front panel. A mechanical shutter only reveals the part of the rotating frequency dial that corresponds to the selected frequency band range.

The characteristic designed band switch is located directly below the dial window, the tuning knob „TUNING“ slightly further right below the frequency dial.

The terminals for connecting aerial „A“ and earth „G“ are located in the bottom right-hand corner of the front panel, with the aerial tuning control above them. Above the nameplate and a panel for accessing the inside of the receiver with the tube sockets is the control for the intensity of the dial illumination.
The operating switch „AVC“ / OFF / „MVC“ is located next to the headphone sockets in the bottom left corner of the front panel, next to it the volume control „INCREASE VOL“ and the BFO pitch control, the switch for the BFO „C.W. OSC“ for receiving CW and single sideband transmissions and the switch for the crystal filter are located directly above.

To operate the receiver, it must be connected to the correct operating voltage; the antenna and the earth wire are connected to the corresponding terminals. The operating switch should be set to „A.V.C“, whereupon the humming of the converter should be audible.

Use the band switch to select the desired range, then use the main tuning knob to tune the signal; the dial runs in opposite directions, i.e. the lower frequencies are on the right and the higher frequencies on the left. The volume is adjusted with the volume control, the BFO switch „C.W. OSC“ should be in the OFF position, the BFO is only activated to receive CW or SSB transmissions, such as those often heard in the amateur radio bands.

The BC-348 is a stable and reliable receiver, but problems can occur with the rotating converter, which works like an electric motor with a coupled alternator - these mechanically moving components are the most susceptible to interference, which is why the sets were occasionally later converted to mains operation by radio amateurs. Main problem in receiver restoration is that many receivers are not in original condition anymore, the valve wiring has been changed to 6.3 V and mains power supplies fitted with partly taking out the typical connectors.

Variants

TypeManufacturerVoltageRemarksFrequencies
BC-348-B „GCT „RCA, 194228V DCDynamotor DM-28-B, without LW/VLF1500 - 3000, 3000 - 5000, 5000 - 7500, 7500 - 10500, 10500 - 14000, 14000 - 18000 kHz
BC-348-C „GCT „RCA28V DCDynamotor DM-28-B, without LW/VLF1500 - 3000, 3000 - 5000, 5000 - 7500, 7500 - 10500, 10500 - 14000, 14000 - 18000 kHz; see B version; later often retrofitted with VLF
BC-348-E „GCT „Stromberg - Carlson, Rochester N.Y.28V DCDynamotor DM-28200 - 500, 1500 - 3500, 3500 - 6000, 6000 - 9500, 9500 - 13500, 13500 - 18000 kHz
BC-348-H „GCT „Belmont, Chicago IL28V DCDynamotor DM-28-H, end tube 6K6200 - 500, 1500 - 3500, 3500 - 6000, 6000 - 9500, 9500 - 13500, 13500 - 18000 kHz
BC-348-J „SET „Wells Gardner28V DCDynamotor DM-28, combined mixer/VFO200 - 500, 1500 - 3500, 3500 - 6000, 6000 - 9500, 9500 - 13500, 13500 - 18000 kHzRadio Receiver BC-348-J
BC-348-K „GCT „Belmont, Chicago IL28V DCDynamotor DM-28see H variant
BC-348-L „GCT „Belmont, Chicago IL28V DCDynamotor DM-28, end tube 6K6see H variantRadio Receiver BC-348-L
BC-348-M „GCT „Stromberg - Carlson, Rochester N.Y.28V DCDynamotor DM-28see E variantBC-348-M (franz.)
BC-348-N „SET „Wells Gardner28V DCDynamotor DM-28see J variant
BC-348-O „GCT „RCA28V DCDynamotor DM-28see E variant
BC-348-P „GCT „Stromberg - Carlson, Rochester N.Y.28V DCDynamotor DM-28see E variantRadio Receiver BC-348-P
BC-348-Q „SET „Wells Gardner28V DCDynamotor DM-28see J variantRadio Receiver BC-348-Q
BC-348-R „GCT „Belmont, Chicago IL28V DCDynamotor DM-28see J variantRadio Receiver BC-348-R
BC-348-S „GCT „Belmont, Chicago IL28V DCDynamotor DM-28, BC-348-C modified / retrofitted with VLF range by Belmont200 - 500, 1500 - 3500, 3500 - 6000, 6000 - 9500, 9500 - 13500, 13500 - 18000 kHz

Technical principle

Radio Receiver BC-348 The BC-348 is designed as a single conversion superhet:

„GCT „ version: The antenna signal is first amplified in two RF stages (V1,V2, each 6K7 (VT-86)), in the mixer stage (V3, 6J7(VT-91)) it is combined with the signal from the receive oscillator (V4, 6C5 (VT-65)) to the intermediate frequency of 910 kHz. After three IF amplifier stages (V5 6K7 (VT-86), V6 6F7 (VT-70), V7 6B8 (VT-93)), demodulation takes place in the diode system of the V7. A 41 (VT-48) or 6V6GT (VT-152) serves as an AF output stage, the second system of the V6 6F7 as a beat frequency oscillator for CW and SSB reception.

Version „SET „: The antenna signal is first amplified in two RF stages (V1 and V2, each 6SK7 (VT-117)), in the combined mixer stage (V3, 6SA7(VT-150)) it is converted with the oscillator signal (V3, second system) to the intermediate frequency of 910 kHz. After three IF amplifier stages (V4 6SK7 (VT-117), V5 6SK7 (VT-117), V6 6SJ7 (VT-116)), demodulation takes place in the diode system of the V7 (6SR7, VT-233). A 6K6GT (VT-152) serves as an AF output stage, the second system of the V7 6SR7 as a beat frequency oscillator for CW and SSB reception.

Tube configuration

Early version BC-348 („GCT „): V1, V2 (each 6K7, RF preamplifiers); V3 (6J7, mixer stage); V4 (6C5, RF oscillator); V5 (6K7, 1st IF stage); V6 (6K7, 2nd IF stage); V3 (6J7, mixer stage). IF stage); V6 (6F7, 2nd IF stage and BFO); V7 (6B8, 3rd IF stage and detector); V8 (41, AF output stage).

Later version BC-348 ( „SET „): V1, V2 (each 6SK7, HF preamplifiers); V3 (6SA7, mixer stage and HF oscillator); V4 (6SK7, 1st IF stage); V5 (6SK7, 1st IF stage); V6 (6SK7, 2nd IF stage); V4 (6SK7, 1st IF stage); V4 (6SK7, 1st IF stage); V4 (6SK7, 1st IF stage). IF stage); V6 (6SJ7, 3rd IF stage); V7 (6SR7, detector and BFO); V8 (6K6, LF output stage); no neon stabiliser.

Development

The BC-348 receiver series was developed at the U.S. Signal Corps Laboratories in Fort Monmouth and the sets were manufactured by various American manufacturers as contractors; the sets from the various manufacturers differed at most in details.
The receivers were the standard receivers of the SCR-287 radio station.

Technically, the receiver was based on the BC-224 developed by RCA around 1935, although that det was still operated with an aircraft on-board voltage of 12 V. At the end of the 1930s, the on-board voltage in more modern aircraft was increased to 28 V, for which the set was redesigned and given the appearance known as the BC-348.

The original BC-348 was developed by RCA and manufactured until 1942. It had the original tube configuration; of the eight tubes, two strings of four tubes with a 6 V heating voltage were connected in series. The earlier sets have a 911 neon stabiliser and a controller for antenna tuning and are easily recognisable by their „grid cap tubes“, tubes with a connection on the tube cap, after opening the cabinet.
As commonly found with U.S. sets, the BC-348s were not only manufactured by the developer company RCA but also manufactured in contracts according to original plans and designs by other manufacturers, suffix letters BC-348-X indicate the contract. The receivers with the suffix B, C, E, H, K, L, O, P & R belong to the older model.

In the middle of the Second World War, a version with a somewhat simplified design was developed; technically, the sets are not identical, but are interchangeable 1:1 due to their dimensions and technical specifications. These receivers have two HF preamplifier stages, a mixer stage, three IF amplifier stages, a duodiode/triode as demodulator, AVC and BFO and a 6K6 as AF output stage; these receivers were easier to maintain and repair, but have the same technical performance.
The receivers with the newer model were also produced in contracts by various manufacturers, they bear the suffix numbers J, N & Q and can be recognised by the „single-ended tubes“, normal tubes without cap connection, and the BFO switch placed further up.

Power is supplied via a „Jones Plug“ (SO-143), a multiple plug in a cut-out on the rear panel, via which the operating voltage is fed in and the line-out audio signal and the transmit/receive switching for muting when operating a connected transmitter are fed out. The receiver was usually mounted on a „Shock Mount FT-154“, inserted into the radio bay in the aircraft and could thus be easily replaced for repair purposes.

Of the more than 100,000 BC-348 receivers produced, many were sold as surplus in the post-war period. The sets, which were designed for operation on aircraft on-board voltage of 28 V DC, were often modified by radio amateurs and in some cases also by dealers, usually by removing the power supply with the dynamotor (rotary converter) to generate the anode voltage and more or less skilfully installing a mains power supply; in some cases, the tube heating was also converted to parallel heating with 6.3 V.

Beautifully preserved BC-348s with shock mount and dynamotor power supply are quite rare today.

The sets from the Surplus were also popular with European armed forces after the war and were occasionally modified for this purpose. In Switzerland, the BC-348 can occasionally be found as a receiver for the H-Station, and Zellweger Uster produced a suitable power supply unit.

In Germany, the set was given a German front panel and renamed as E 348 A and B. With the U-28 converter, the set was converted to 12 V operation with 12 V heating voltage and a mains power supply unit was also developed for it.

In France, the BC-348 was produced under licence or „refurbished“; in any case, the BC-348 is occasionally found in Switzerland with a front panel labelled in French.

Abroad - Variants

TypeManufacturerVoltageRemarksFrequencies
H-receiver CH around 194528V DCConverter DM-28 200 - 500, 1500 - 3000, 3000 - 5000, 5000 - 7500, 7500 - 10500, 10500 - 14000, 14000 - 18000 kHzRadio Receiver BC-348-R
E-348-A D around 194712V DCConverter U 28 200 - 500, 1500 - 3000, 3000 - 5000, 5000 - 7500, 7500 - 10500, 10500 - 14000, 14000 - 18000 kHz
BC-348-J F around 194728V DCConverter DM-28 200 - 500, 1500 - 3000, 3000 - 5000, 5000 - 7500, 7500 - 10500, 10500 - 14000, 14000 - 18000 kHz; L.G.T. St.Cloud
BC-348-M F around 194728V DCConverter DM-28 200 - 500, 1500 - 3000, 3000 - 5000, 5000 - 7500, 7500 - 10500, 10500 - 14000, 14000 - 18000 kHz; L.G.T. St.Cloud

Technical documentation

Further information

en/bc-348.txt · Zuletzt geändert: 2024/08/04 09:36 von mb