Signal Tracer and Capacitor Tester (T1241E)

This mains powered two-in-one instrument was found in a Radio Craft from March 1948. The headphone must be high impedance.

Transistorized Intercom (CB11211E)
This circuit was obtained in an old magazine from the 1970s. The circuit can still be assembled with...
Modulated Oscillator (CB22067E)
This power oscillator uses an LM380 amplifier. We found it in old English documentation. The C3...
Zener Load Protection (CB4141E)
In the figure we show a simple way to use a zener diode to protect a load against overvoltage. The...