05-03-2013, 07:30 PM
Thank you for the comments Gentlemen. Unfortunately I fear that the circuit that I have is a lot different.
So, another sunny day and another couple of hours in the Garage. It can't last, and indeed the Forecast says so
Step one was to snip out the broken Hunts and test it. It really is 0.01uF 400v so at least that matches the Diagram. It appears to be completely O/C and measures about 45pF on my Cap. Meter. So what's new?
Next I tacked in a replacement, and ........ no change. Ah, well.
So a bit of measurement and reverse-Engineering is called for. The PCB is mounted on 6 pillars. Fortunately I have a Nut Spinner just the right size so it wasn't too bad. I removed the EHT Lead and the Bright-up line and managed to turn it over. The Bright-up line arrives on a pillar below the PCB and has -150v on it, so there's plenty of scope (sorry) for getting the back of my hand on it. All is nice and clean and nothing looked singed. While I was at it I put the replacement C502 in properly. I decided a bit of voltage measurement would be a good start - see attached.
V501 would appear to be either cut off or duff. The latter seems more likely as there's only -4.6v on the Grid assuming my measurements are OK so it should be conducting.
I'll have a look for dry joints, measure the Resistors and get a couple of Valves on order. While I'm waiting I'll see if I can sort out the circuit.
Alan
So, another sunny day and another couple of hours in the Garage. It can't last, and indeed the Forecast says so
Step one was to snip out the broken Hunts and test it. It really is 0.01uF 400v so at least that matches the Diagram. It appears to be completely O/C and measures about 45pF on my Cap. Meter. So what's new?
Next I tacked in a replacement, and ........ no change. Ah, well.
So a bit of measurement and reverse-Engineering is called for. The PCB is mounted on 6 pillars. Fortunately I have a Nut Spinner just the right size so it wasn't too bad. I removed the EHT Lead and the Bright-up line and managed to turn it over. The Bright-up line arrives on a pillar below the PCB and has -150v on it, so there's plenty of scope (sorry) for getting the back of my hand on it. All is nice and clean and nothing looked singed. While I was at it I put the replacement C502 in properly. I decided a bit of voltage measurement would be a good start - see attached.
V501 would appear to be either cut off or duff. The latter seems more likely as there's only -4.6v on the Grid assuming my measurements are OK so it should be conducting.
I'll have a look for dry joints, measure the Resistors and get a couple of Valves on order. While I'm waiting I'll see if I can sort out the circuit.
Alan
