FSK keyboard (CB21758E)

This circuit was found in documentation from 1977. Its purpose is to diode-switch the frequency of a VFO. The frequency depends on the oscillator.

Level change circuit with negative output (CB21597E)
Found in documentation from ON Semiconductor, this circuit provides a rectangular output signal with...
20 kHz counter with SCS (CB6614E)
We found this circuit in 1964 General Electric documentation. The circuit works with mechanical...
1 Hz Active Filter (CB6721E)
This very low frequency circuit was found in a 1964 Electronic Design. Transistors may be modern...