This variable filter circuit was found in July 1975 Radio Electronics magazine. The circuit uses 3 general purpose op-amps like the 741 and must use a symmetrical source.
This circuit was found in a 1977 radio amateur manual. Integrated circuits are operational...
In the figure we show a configuration for a crystal-controlled overtone oscillator using a...
The transistor used is a high current Darlington, but an equivalent discrete configuration can be...