Amplified megaphone (CB23703E)

This is an improvement on the previous circuit with a preamplification stage. The circuit is from an October 1960 Radio Electronics magazine.

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...