This bank of switches can be programmed in a variety of ways for logic experiments. The circuit is from August 1986 Radio Electronics magazine.
Published in Popular Electronics with the curious name of Obnoxious Noisemaker, this 1968 circuit...
This simple converter does not use a transformer and the transistor can be the BD135 for currents up...
This circuit is from a 90's publication but uses components that are still common in our market....