This 6-transistor circuit had excellent sensitivity using germanium transistors. The push-pull stage used two transformers, one drive and one output as we usually find at the time.
This circuit is from Motorola documentation on 1976 power devices. SCRs are powered according to...
Assembled with SMD components this spy can be made very small. We found it in an Australian...
We found this circuit in an old documentation. The operational amplifier of the time can be...