Leak Detector (CB22456E)

We found this circuit in a Popular Electronics from 1992. The transistor is general purpose, assuming equivalent.

Pure sinusoidal oscillator (CB9190E)
This circuit generates a sinusoidal signal with only -80 dB THD. The circuit was found in a 90's...
Sencore transistor test (CB22546E)
This test, the commercial transistor tester, had its diagram published in an article in Radio...
Adjustable Regulator LM323 (CB15319E)
This circuit can supply voltages in the range of 8 to 20 V with a maximum current of 3 A. The...