This traditional configuration found in a Radio Shack document can use 2N2646. More keys can be added, and the power can be supplied with voltages from 9 to 15 V.
The transistor can be a modern equivalent and the transformer is the type of output found on an...
The output voltage of this unit is approximately 1.4 V less than that of the chosen zener. The...
We found this circuit in an English publication from the 80's. The circuit uses current components like...