This 5.1 MHz circuit was found in a 1980s documentation. The frequency is given by the crystal and general purpose transistors can be used.
This simple strobe light is from an article in 1982. Its complete circuit, very simple, appears in the...
This power step for relay activation was found in the 1964 RCA transistors manual. The circuit is of the...
This circuit, bridge type, was found in American documentation from the 60's. The transistor is...