This two-transistor circuit is from a December 1964 Radio Electronics. Modern transistors can be tested. The headphone must be high impedance or crystal with a 2k2 resistor in parallel.
A touch of the sensor makes the load bistable (load) connected in Q1. For a BC548, a 6 V or 12 V...
With the use of an additional diode and a resistor, the configuration of the figure can be...
This circuit was found in documentation from the 1980s. The circuit uses several components of the...