Intercom (CB21660E)

This good gain circuit was found in a Popular Electronics from April 1967. The transistors are germanium of the time.

Turns Counter (CB18037E)
This is a project that can easily be adapted for other purposes such as counting people, objects,...
Modulated Siren (CB12728E)
A modulated (intermittent) siren, using the four gates of the 4001 integrated circuit is shown in the...
Universal Battery Charger (CB24984S)
This circuit was found in July 1986 Radio Electronics magazine. The maximum current is 1.5 A. The...