Two-tone solar buzzer (CB20493E)

This circuit was found in a 1991 publication. The transistor can be a general-purpose type.

Unijunction with bipolar transistors (CB23698E)
In the figure we have a circuit that simulates a unijunction transistor in an oscillator obtained from...
Wireless Audio Link Receiver (CB25157S)
This is the receiver for the earlier system published in the August 1988 Radio Electronics...
Peak Detector with Operational (CB15808E)
Two National Semiconductor operatives are used on this circuit indicated for instrumentation...