Found in American documentation from the 1980s, this circuit has a throughput of 700 Hz and a flat response of 400 to 500 Hz, with crystals of 3 MHz. Crystals of 2 to 15 MHz can be used.
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...