This drum amplifier was found in an American documentation from 1947. It makes use of a mechanical vibrator to generate high voltage for the tubes.
This circuit is from Popular Electronics from the 90's. The circuit discharges the battery with a...
We found this circuit in the October 1993 Electronics Now magazine. The 4-channel circuit is...
With the appropriate choice of C1 and C2 it is possible to divide the frequency of a rectangular 3 V...