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.

5 Voltage Level Indicator (CB4892E)
This circuit is based on an uncommon Texas component today, as found in an American 1980s...
Audible warning (CB9204E)
This circuit that generates a special sound was found in a Popular Electronics from the 90s. The...
LM3900 Current Source (CB25178E)
This circuit uses a LM3900 Norton amplifier and a 2.7 V zener diode to supply a current of 1 mA to...