The transistor on this mixer can be any general-purpose transistor. The number of entries can be changed. We found it in an old documentation. Input and output cables must be shielded.
Found in a 90s Popular Electronics, this circuit triggers a load from the audio signal applied to...
This old receiver (1967) uses germanium transistors from the time and coupling transformers,...
I found this circuit in a Popular Electronics from 1992. The circuit can be easily implemented with BC549...