Found in a 1949 Radio Electronics, this 4-tube circuit was fed directly from the mains with a half-wave rectifier.
This circuit was obtained in the magazine Eletronica Prática 9 of 1977. The Italian magazine no...
This circuit was found in the 1960 Mullard transistor reference manual. The circuit can be...
The circuit presented may use any general purpose transistor. The indicator is an LED and...