Null Indicator (CB21930E)

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

Bargraph Battery Tester (CB26313E)
Found in an issue of Elektor magazine in the 90s, this battery tester is based on the LM3914. The...
Intercom (CB4572E)
I found this circuit in a July 1982 English magazine. The circuit is still viable by simply using...
Up to 60 seconds timer (CB21430E)
This circuit is from a 1966 Motorola Field Effect Transistors Manual. The circuit makes use of...