RCA BC-224-A - the First BC-348

The mid to late 1930s reflected a curious mixture of old and new thinking in aircraft radios, led by brilliant engineers in such companies as Aircraft Radio Corporation and RCA. The example below should endear itself to every radio amateur growing up in the 1940s or 1950s, because it was the first of the BC-348 series of aircraft receivers. A clos
RCA BC-224-A - the First BC-348 - schematic

e look at its front panel will reveal the same controls that are on all the later BC-224/348s, with the addition of a "heater" switch that provided power to the thermostatically regulated local ("heterodyne") oscillator compartment to provide stability at high altitudes, and some relocation from the more familiar positions of the others. (The BC-348-J, N, and Q also deleted the antenna alignment knob, of course. ) This innovative receiver has a circuit diagram that looks very similar to its later counterparts, as well. There was a curious inclusion of a short transmission line between the left and right side of the receiver along the bottom edge of the front panel, presumably to make antenna connections easier on some aircraft installations. A short wire from the "A" terminal on the left to an inexplicaby different shaped terminal 45 ° downward from it was required to connect the transmission line. The familiar PL-Q103 and PL-P103 eight pin Jones style power plugs were identical to the later models, and though the FT-154 shock mount did not have the same depth as the later FT-154-*, it appears identical to the casual glance. Installed in a typical setting, a BC-224-A (above) in NASM`s unrestored O-47A observation aircraft shows its age, but also the ambience of an operational aircraft communications receiver. The tuning knob has suffered from deterioration of its paint in the storage environment for so many years, but also...

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