Phone Call Amplifier (CB21271E)

This circuit was found in an old Electronics Now. The transistors are general- purpose and the circuit is powered by an external source.

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HeNe LASER power supply (CB9444E)
This circuit is from Radio Electronics from the 90s. It supplies a voltage between 800 V and 2 000...
Cable Locator (CB21303E)
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Light out switch (CB8331E)
This highly sensitive circuit was found in a 1967 General Electric SCR manual. Equivalent...