The circuit shown was found in a 1967 RCA manual. Modern equivalent components can be used. The SCR must be according to the controlled load.
This low frequency oscillator with an operational amplifier of type 741 has adjustment of the mark...
This circuit was found in a Popular Electronics from the 90s. Transistors are general purpose...
The AT21CS11 memory device offers an extended voltage range to accommodate lithium-ion battery...