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.

S meter (CB1439E )
This S-meter circuit was found in a 1976 publication. The circuit is used to measure the signal...
Magnetic Phonocaptor Preamplifier (CB16663E)
Several versions of this circuit can be found on this website. This makes use of FETs that can...
Frequency Modulated Siren 555 CMOS (CB15868E)
With the circuit shown in the figure we have a frequency modulation which is produced by a...