Audio Generator (T1281E)

This 5-tube audio generator is from a Radio Craft from July 1948. The circuit has 3 frequency bands selected by a switch through capacitors.

Sequential LED (CB7046E)
This circuit was obtained in an old Popular Electronics. It makes use of quite common components....
Negative Voltage Generator 555 (CB25546E)
This polarity inverter circuit for voltages down to about -12 V was found in the December 1992...
Easy Tuning Square and Sine Oscillator (CB4927E)
We found this circuit in an American 1980s documentation. The circuit can be assembled with modern...