The VT-136 (commercially 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. The base looks like UX7 but is slightly different and is designated as U7B (medium).
The parameters given are for single ended use. 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 (shown in the lower table) 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.
The elliptical lower screen places this as part of the 807 family.
The envelope has the commercial Type designation on it. The base cap carries the USA government code VT-136.
The 1625 within an octagonal border.
The RCA logo on the base cap.
The classic envelope is 51 mm in diameter and, excluding the UX7 base pins, is 126 mm tall.
