Low battery indicator 555 (CB9551E)

This circuit can operate with different voltages, depending on the zener used. We found it in a 90s American documentation.

Standing wave alarm (CB8986E)
This circuit triggers a warning LED when the standing waves reach a high value. The circuit was...
Symmetrical Regulator LM380 (CB5879E)
This 80's circuit uses an audio amplifier to obtain a symmetrical source from a single source. The...
Audio Oscillator (CB22017E)
The frequency of this oscillator depends on T1 and C2. The transformer may be of the old audio...