This circuit is from an old American documentation from the 70s. Transistor 2N3904 can be replaced by BC548. The relay must have 100 mA of maximum current.
This three-transistor circuit was found in Radio Electronics magazine from May 1969. The circuit is...
This beat frequency oscillator was found in a 1980s documentation. The original FET has a grounded...
With this circuit it is possible to make the selection of transistors and their test according to the...