Intercom (CB21660E)

This good gain circuit was found in a Popular Electronics from April 1967. The transistors are germanium of the time.

Voltage Controlled Oscillator (CB14355E)
This circuit was found in the Linear Applications Handbook of the National Semiconductor of 1994....
Operational with Failure Test (CB3951E)
This circuit has been found in operational documentation of the 1970s. The circuit has a fail-safe...
Signal injector (CB23619E)
This simple signal injector was found in a Radio Electronics from July 1959. The transistors are...