Crystal oscillator with a 6A6 (T437E)

We found this circuit with the 6A6 double triode in a 1938 Radio Handbook. The power source is not provided.

Astable (CB19898E)
This astable multivibrator is one of the many configurations that we have in this section and on...
Fox Hunting Transmitter (CB20411E)
This little transmitter was found in a documentation about the transmitter being intended for the...
Regulated power supply (CB23737E)
This power supply circuit, slightly different from the conventional one, was found in the Radio...