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.

VCO 4049 (CB15463E)
A simple version of VCO CMOS using 4049 inverters is shown in the figure. This circuit can be...
aaaa SCR oscillator for code practice (CB8795E)
This simple SCR relaxation oscillator was indicated by a 90s Popular Electronics. The frequency is...
Customer Service Counter (CB6141E)
This circuit can be used as an answering password system in a store, office, or other location....