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.

Digital Band Pass 10 to 20 kHz Filter (CB13536E)
This circuit was obtained in the 1977 RCA CMOS manual. The circuit has the frequencies determined by the...
Multiplex Series Lamp (CB6874E)
We found this circuit in a 2004 documentation. The circuit consists of a standard lamp for testing...
Difference Amplifier (CB6429E)
Found in a Popular Electronics of the 90s this configuration can be seen elsewhere on our site....