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 Calibrator II (CB19746E)
We found this circuit in an old documentation. It has a thermally compensated voltage reference. The...
Benchtop Amplifier (CB6978E)
Suggested by a Popular Electronics, this small amplifier that has a detector to follow RF...
LM393 Delay Generator (CB4486E)
The presented circuit generates a pulse whose delay in relation to the input depends on RC. These...