This sound or voice relay was found in a Popular Electronics. It includes an amplification stage and can be used as a shield.
This circuit appears in similar versions on this site. This is from a Popular Electronics from the 80's. The...
Indicated for discriminators adjustment in FM and VHF receivers, this circuit was found in a 90s...
The sensor for this circuit, found in an English publication in 1983, is a germanium transistor....