Equivalent operational amplifiers can be used on this crystal-controlled oscillator. The circuit is from old documentation and can be changed to operate on other frequencies.
We found this circuit in the 1960 Mullard transistor reference manual. The phototransistor can be a...
We found this circuit in a manual from the 80's. The circuit is valid for any operation and the...
Advertised as the world's simplest circuit for a Z80, this one is from Radio Electronics magazine,...