Constant current source (CB20484E)

This circuit uses a current regulator from the 90's. This component is uncommon nowadays. The transistor admits equivalent.

Tuned audio oscillator (CB22254E)
This circuit is from a publication from the 50's. Inductive components are critical, and...
Stereo Pre Amplifier (CB18559E)
This simple two-transistor circuit used transistors from the 60s, having been found in a...
Capacítancemeter (CB3878E)
This circuit uses an oscillator that generates a signal of approximately 1450 kHz to test...