Found in a 90s Elektor, this circuit makes use of general-purpose transistors, except T4 that can be replaced by an equivalent.
This LM139, 239, or 339 comparator configuration appears elsewhere in this site and this section....
This circuit can operate with signals from 1.5 to 150 MHz. C1 is 36 pF and C2 is 4n7. The diode...
This circuit consists of a relaxation oscillator that generates high voltage pulses in a flyback...