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.
This filter was found in a 1975 American technical publication. The filter can be of any type and...
This motor logic control was found in the September 1985 issue of Radio Electronics magazine. The...
This configuration can be found elsewhere on this website and section. The circuit is from Popular...