MOSFET Amplifier Stage (CB26315E)

Found in a 1990s Popular Electronics, this circuit uses a small transformer matched to the impedance of the speaker being driven.

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Narrowband Audio Filter (CB20085E)
We found this circuit in an old American publication from the 1980s. Transistors can be...
Tester with FET (CB13783E)
This very sensitive circuit works almost like an electroscope. The FET can be the BF245 and it...
transistorized differential amplifier (CB25639E)
This circuit uses matched transistors. The circuit is from Electronics Now magazine and has a...