Null Indicator (CB21930E)

This bridge was found in a Raytheon transistor manual from the 1960s. The transistors are germanium from the time.

Switch Amplifier (CB21820E)
A circuit for controlling the temperature of a heating element was found in a Mullard transistor manual...
Proximity switch (CB22444E)
We found this circuit in a 1992 Popular Electronics. The circuit has an optical sensor with LED...
Touch Oscillator (CB11575E)
I found this circuit in an old English magazine from 1979, but it can be easily assembled with...