Current shield RS232 (CB8075E)

Found in a Popular Electronics from the 9s, this circuit has output for RS-232 interfaces and current input. The power supply must be symmetrical.

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Old Phase Shift Oscillator (CB13956E)
The circuit presented was found in a documentation from the 1950s, generating a sinusoidal signal...
100 gain amplifier with LM381 (CB25272E)
We found this high gain circuit with the LM381 preamplifier in a Radio Electronics from February 1990....
Negative Feedback Stage (CB6131E)
This circuit is from a 1967 US publication. The configuration can serve as a basis for designs...