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.

Automatic Battery Charger (CB10565E)
This circuit is from a 1987 magazine, but it can still be easily assembled, as the components are...
Bargraph Humidity Indicator (CB11519E)
This circuit was found in a Popular Electronics from 1991. The transistor could be the BC548. The...
Capacitive Differential Meter (CB9493E)
This circuit, which can be used to indicate the movement of an object, was found in NASA...