Crystal variable oscillator (CB9506E)

Found in Radio Electronics from the 90s, this circuit can vary the frequency in small values around the crystal frequency.

Analog Frequency Meter 555 (CB22164E)
This low frequency analog frequency was found in documentation from 1989. The circuit has 5...
High stability thermocouple amplifier (CB20684E)
This circuit was found in an American documentation from the 90s. It can be implemented with...
VLF Oscillator (CB21139E)
This very low frequency oscillator was found in a Popular Electronics from the 90s. The circuit...