A modified and improved Hornby Skewes silicon Zonk 2 that goes for big bucks.
Schematic and a breadboard session(!) is avaiable HERE.
It seems that silicon transistors in the 150-200 hFe range works best in this circuit.
*Update 240203* Reeves Electro got in touch with Gray Bench since two of the pot values was incorrect in the trace. Layout and schematic is updated.
Schematic
