This circuit was found in a 80’s American documentation. The adjustment trimpot is from 47k to 100k. The diodes are general-purpose types use and the supply voltage depends on the relay.
The purpose of this 1985 circuit is to make the sound test of type 106 SCRs (MCR106, TIC106,...
Using the CMOS 4001 we found this circuit in the October 1974 Radio Electronics magazine. The...
We found this circuit in a 1957 Raytheon transistor publication. The circuit can be assembled with...