This circuit is from the Motorola Linear Databook of 1990. The coils must be according to the frequency of the signal.
This circuit for common analog telephones was found in March 1982 Radio Electronics magazine. It...
We found this circuit in an English publication from the 1980s. The transistor can be BC548 or...
Found in a 1967 RCA documentation, this circuit can be made with equivalent SCRs according to the...