No signal alarm (CB22300E)

This circuit trips a relay when it stops receiving a signal. The transistor is germanium. We found it in a publication from the 60s.

Continuity tester (CB9326E)
This circuit was obtained in an Electronics Now from the 90s. The circuit uses operational...
Physiotherapy Ultrasound (CB16841E)
This circuit operates at a frequency around 1 MHz, having been found in a technical documentation from...
Integrated Transmitter without Coil (CB14821E)
The TAA131 used in this circuit is not very easy to find today, but an equivalent low power audio...