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 circuit in a receiver that allows the capture of distant stations with short waves. The...
This was a very popular instrument in the workshops of the 60s and 70s. It was a "top of the line"...
This source is more elaborate than the previous one because it uses two transistors. The source is...