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.
Found in a 90s Popular Electronics, this circuit is based on a uA739, an unusual component today....
This circuit is from a 1982 publication. It is a sequential effect of accelerated LEDs. The...
In the figure we have more circuit that makes use of transistors and that has excellent...