1-Ttube reflex receiver (T1555E)

This one-tube circuit is equivalent to the previous one. We find it in a 1924 book by Gernsback, Power is made by batteries.

Humidity Relay (CB18619E)
This moisture-activated relay was obtained from an American documentation from the 1980s,...
TV antenna compass (CB22311E)
Found in an old American publication, this circuit indicates the direction the antenna is pointing in...
Power Usage Monitor (CB24827E)
We found this circuit in Radio Electronics magazine from August 1984. The circuit aims to control the...