BC - 312 US Army communications receiver

MY VINTAGE EQUIPMENT

Owner   Rudolf  Bosnjak  - E71RB, Sarajevo, Bosnia and Herzegovina.

INTRODUCTION

The BC-312 is a 9 valve communications receiver, a superheterodyne design using single conversion. It was made in the USA, and designed at Fort Monmouth, in the mid 1930s. It was intended for ground use, either individually or with a transmitter. It can receive AM (amplitude modulation) or CW (continuous wave) or MCW (modulated continuous wave) signals, and uses the LS3 loudspeaker. It looks similar to the BC-348 airborne receiver, having a wedge-shaped dial, but the radio is much larger, heavier, and very different inside. The BC-312 weighs 48 pounds.

The receiver covers 1.5 to 18 mHz, in 6 ranges. They aree
Band A: 1.5 C 3.0 MHz
Band B: 3.0 C 5.0 MHz,
Band C: 5.0 C 8.0 MHz,
Band D: 8.0 C 11.0 MHz
Band E: 11.0 C 14.0 MHz
Band F: 14.0 C 18.0MHz.

It has two RF amplifiers (Radio Frequency) using VT-86 (6K7) valves, a frequency changer using VT-87 (6L7) with a separate oscillator using a VT-65 (6C5), two IF amplifiers (Intermediate Frequency) using VT-86 (6K7), a detector and audio pre-amplifier using a VT-88 (6R7), an audio power amplifier using a VT-66 (6L6) or 12A6. There is also a crystal filter and a BFO (Beat Frequency Oscillator) using a VT-65 (6C5). The internal power supply can be a 12 or 24 volt dynamotor or a 115 volt AC supply. The IF is at 470 kHz. The receiver is very nicely made, with several castings and a steel case, so it is very heavy. It is also very stable and nice to use with the vernier dial. The front panel is distinctive as it has a large connector pointing downwards, not outwards as is usual. This is for power input, audio output, or connection to a transmitter. The receiver can then be a transmitter remote control, as it has a key, a microphone jack, and a Send Receive switch.

MODELS
There are many models in the BC-312 family, 30 variations in all, denoted by a number with a letter suffix. They all look the same, but a close inspection reveals the differences. They can easily be divided into two groups, the HF versions consisting of 22 models, and the MF versions consisting of 8 models. The HF frequency coverage is 1.5 C 18 MHz, and the MF frequency coverage is 150 C 1500 kHz. The HF versions can be further divided into two categories, the DC powered models, all called the BC-312, and the AC powered models, all called the BC-342. Similarly, the MF versions can be divided into the DC powered models, all called the BC-314, and the AC powered versions, all called the BC-344. Strictly speaking then, there are only 13 models of the BC-312, 9 models of the BC-342, 6 models of the BC-314, and 2 models of the BC-344.

The power supply is modular and can be easily replaced, the DC dynamotor supplies are either 12V or 28V DC. The early supply is a DM-17 and the later model is a DM-21. The 115V AC supply is an RA-20. The two 28V models are denoted by an X, and use a 12A6 instead of a 6F6 as the audio power amplifier. One of the early uses was in vehicles, so a noise antenna was fitted and there was a separate connector for the noise antenna input. A control allowed the noise to be canceled out, which is useful for ignition noise. This model is obvious as it has an extra connector and two snap covers on the lower left hand side. Most models were fitted with a crystal filter, and the phasing control was at the top right hand side. The other models had a dial light dimming control in this position. Some later models had raised lettering as opposed to engraved lettering, and some had a watch holder near the nameplate. Other models were basically the same, and the model number indicated the number of audio jacks, minor electrical and mechanical differences, and the identification of the manufacturer.

SPECIFICATIONS

INDEX