… while waiting for some replies to my post I tried increasing the final load resistance by adding a small 5 megohm potentionometer in series with R12 and the tube.
By adjusting the pot, I can make the circuit work at a setting of 3 megohms additional resistance. I.e. the LED blinks randomly at approx 150 cpm.
But it was very unstable, the plateau is very narrow and it only works for a few minutes. Then the circuit went into a ‘dead state’ where nothing worked at all. Finally recovered after a day of rest, so I removed the extra megohms.
I think the solution is to find the optimum resistance for the final two series resistors R11 and R12 to match the SI-180G load resistance, which is documented as 5-10 megohms.
Has anyone had any success in matching this Twig circuit to other tubes besides the J408Y?
Tnx,
John/af4ex