This circuit for very low frequencies was found in an American documentation from the 90's. Transistors are for general use and the frequency depends on C1 and C2.
This circuit for VCR recording heads was found in the February 1990 issue of Radio Electronics magazine....
This very simple continuity tester uses a small 1.5 V lamp (type used in flashlights). Can be...
This commercial radio with 3 earphone listening transistors was manufactured in Japan in the...