Suggested by Philips documentation from 1968, this circuit uses components from the era that can be replaced by modern equivalent types. The double transistor can be replaced by a matched pair.
This circuit with unijunction transistors was found in a documentation from the 80's. The trigger...
In this circuit of an old American documentation, the input impedance is the same as the output...
In the figure we have the way to obtain a voltage of 18 V from a 6.3 V transformer with central...