RCA transmitting valve

1950s in United States

RCA transmitting valve FC13; Type no. 1625

From the National Valve Museum:

The 1625 is electrically identical to the 807, except for the heater requirements and base cap. At 12.6 Volts the 1625 would have been designed for mobile equipment. When used in a class AB1 push pull pair with 600 Volts on the anode an output power of 65 Watts was normal. These valves were much used in medium power amateur radio transmitters for high level modulation. In this use the output transformer, called a modulation transformer, would be impedance matched to the anode circuit of the RF power valve. The audio power would increase or decrease the amplitude of the RF envelope.

The 807 itself was a workhorse of the HF bands. As a transmitter power amplifier operating in class C producing 40 Watts of RF, it would need a pair of in push pull to generate the 20 Watts of audio required to fully modulate the valve. Other modulation systems operating on the screen grid would require much less audio drive but with less RF output.


Radio Communication
Object Number:
glass, metal (unknown) and plastic (unidentified)
  • object genre
  • component parts
  • mechanical component
Gift of Dr. G. R. Airth

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