This circuit is from a Radio Electronics magazine from August 1974. It used one of the first photomultiplier tubes that was to be powered by high voltage. The power came from the mains.
This circuit using an operational amplifier was found in old American documentation. It can be...
If the circuit oscillates, emitting sound, it is because the transistor is good. This simple...
Like the previous circuit, this is used in the analog part of the telephone lines. The same...