This is an amplifier circuit intended for modulating transmitters. The 5-tube circuit is from an American manual from 1947. The power supply uses a transformer.
This circuit with variable capacitance diode (varicap) is from a publication from the 90s. The...
With this circuit it is possible to divide the frequency of a rectangular signal by values between 2...
The presented circuit uses an optocoupler to trigger a triac. We found it in a Popular Electronics from...