This circuit was found in a 1967 General Electric documentation. Tunnel diodes can oscillate at very high frequencies. These are not currently easy to obtain components.
This circuit is from a 1995 technical documentation. The transistor can be a BC558 and the sensor...
Found in a Popular Electronics from the 90s, this circuit checks the presence of voltage on a...
The critical component of this amplifier is the output transformer. We found the circuit in an old...