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.

Rain Alarm (CB15108E)
This alarm, from a 1996 magazine, can be fitted with two BC548s in the original configuration...
Simple touch switch (CB9563E)
Using only one general purpose transistor this circuit is powered by batteries. The lamp of the...
Programmable attenuator (CB9031E)
Can be used as a shield, this old American documentation circuit offers digitally selected...