This circuit is from a 60's documentation. The capacitance C1 can be between 20 pF and 0.01 uF depending on the generated frequency. Equivalent transistors may be employed.
The circuit illustrated in Figure allows external loads (8) to be driven from parallel port...
This circuit uses two transistors to simulate the action of an SCR on a regenerative switch....
The filter presented is from 1994 but can be implemented with a more modern equivalent. We found...