This circuit was found in a 1968 General Electric manual. The circuit is for 3 A motors but can be changed according to the SCR used. The SCR is type 106 and R1 is 10k.
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...