This amplifier was found in a tube equipment manual from 1947. The high-fidelity circuit has pentode tubes at the output and a source with transformer.
This circuit is from Popular Electronics of the 90's. It makes use of NO and NC sensors. The relay...
Based on TTL logic this circuit can vary both the frequency and the pulse width of a rectangular signal....
This circuit was found in an old English publication. The circuit makes use of general-purpose transistors....