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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Constant Light (CB15552E)
The basic idea of the circuit shown in the figure is to increase the brightness of an ordinary...
LED beacon (CB20490E)
This sole beacon which has a battery charged by photocells was found in documentation from 1991....
Impedance Matcher (CB15540E)
Many oscilloscopes have high impedance inputs that make it difficult to observe high frequency signals...