1940s commercial receiver (T1618E)

This receiver was found in a Radio Electronics from 1949. It is a superheterodyne of the time using 6 tubes.

Spy Amplifier (CB21644E)
This stethoscope or hearing aid amplifier has excellent gain. It was found in Popular Electronics from...
Bistable with the LM3900 (CB14202E)
We found this circuit in the National Semiconductor's Linear Applications Handbook of 1994. The...
Linear Resistance Meter (CB12477E)
Found in a 1979 documentation, this circuit measures resistances on 5 linear scales. The precision is...