29-05-2021, 10:05 AM
Can't find the fault, it appears to be very low frequency instability causing the HT, bias etc to go haywire. Here's a link to a video - https://youtu.be/Tsd859OvDDI of a scope trace monitoring the HT. It's a bit hard to see but there is periodic rising and falling of DC, followed by what looks like static, odd.
One other indicative symptom is the screen grids or at least one of them is drawing a hell of a lot of current, causing a stopper resistor yesterday issuing smoke. There is also a periodic clicking from the OP valve/s followed by "fizzing",this is maybe what we are seeing on the scope trace? Could it be there is a anode/g2 or similar inter electrode short?
I've swopped OP valves, moved grounds and tried another screen grid supply,no improvement.Any ideas?
Andy.
One other indicative symptom is the screen grids or at least one of them is drawing a hell of a lot of current, causing a stopper resistor yesterday issuing smoke. There is also a periodic clicking from the OP valve/s followed by "fizzing",this is maybe what we are seeing on the scope trace? Could it be there is a anode/g2 or similar inter electrode short?
I've swopped OP valves, moved grounds and tried another screen grid supply,no improvement.Any ideas?
Andy.
