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 was obtained from an English magazine from 1976. The circuit operates two LEDs and...
Found in a publication from the 60's, this power supply has no regulation, but only current...
This circuit can use the LM148 and its more modern equivalents, generating a sinusoidal signal whose...