In fact, this circuit from the 60's applies to photographic printers of the time, timing the lighting of a 20 W lamp. The components are from the period.
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...