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.

Voltage Drop Alarm (CB1530E)
This circuit goes into operation producing a sound on a small speaker when the supply voltage...
Speaker Protector (CB25397E)
We found this circuit that protects speakers against current surges that occur when the amplifier is...
Bipolar Transistor Colpitts Oscillator (CB4582E)
The oscillator shown in the figure can generate signals between 3 and 15 MHz approximately, depending...