Door buzzer or alarm (CB20492E)

This solar powered circuit was found in a 1991 documentation. The transistor is a general purpose NPN.

LED drive I (CB18890E)
This circuit drive an LED with constant current determined by the values of the resistors of 10...
50MHz Oscillator (CB22577E)
This transistorized oscillator was published in the July 1953 issue of Radio Electronics....
Digital Volume Control Treble and Bass Balance (CB4576E)
This circuit is from 1995 documentation. Integrated circuits are used which can still be found...