30-04-2013, 09:02 PM
On reflection I decided I'd better do some measurements before tidying things up.
So:-
I can't set the 300volts high enough and I could before. Possibly something is taking more current than before although it won't be the EHT Board as it only feeds the 5763 Screen and the 12AU7 Anodes via big Resistors.
The Oscillator is running at 50kHz - 20uS - and there's well over 400v p-p on the 5763 Anode. I tried the 'old' valves and they're not as good.
The EHT Pot doesn't do much, and the outputs aren't very stable.
All the outputs, apart from the PDA which I haven't measured, are about 20% low. That's compared to the voltages in the Manual.
The Timebase isn't running.
There's now a nice big unfocussed blob on the Screen. It can be varied with the controls, but not turned down.
I've modified the Brilliance area of the Diagram to make it more logical, see attached.
What next?
I think I'd better do some more measurements round the EHT Board to see how the Control Circuit reacts to the Pot.
After that I think I'd better measure the Tube Base voltages. The back panel looks as though it comes off fairly easily. There's an odd 'big drip' on the inside, much like a melted Transformer although there's nothing anywhere near.
A blast if Switch Cleaner round the Timebase switches and Valves will probably be beneficial.
As the voltages are all low should I change the other Rectifiers? Presumably they're all the same age.
We've got a visitation from relatives for the next few days so things will be a bit 'slow'
Alan
So:-
I can't set the 300volts high enough and I could before. Possibly something is taking more current than before although it won't be the EHT Board as it only feeds the 5763 Screen and the 12AU7 Anodes via big Resistors.
The Oscillator is running at 50kHz - 20uS - and there's well over 400v p-p on the 5763 Anode. I tried the 'old' valves and they're not as good.
The EHT Pot doesn't do much, and the outputs aren't very stable.
All the outputs, apart from the PDA which I haven't measured, are about 20% low. That's compared to the voltages in the Manual.
The Timebase isn't running.
There's now a nice big unfocussed blob on the Screen. It can be varied with the controls, but not turned down.
I've modified the Brilliance area of the Diagram to make it more logical, see attached.
What next?
I think I'd better do some more measurements round the EHT Board to see how the Control Circuit reacts to the Pot.
After that I think I'd better measure the Tube Base voltages. The back panel looks as though it comes off fairly easily. There's an odd 'big drip' on the inside, much like a melted Transformer although there's nothing anywhere near.
A blast if Switch Cleaner round the Timebase switches and Valves will probably be beneficial.
As the voltages are all low should I change the other Rectifiers? Presumably they're all the same age.
We've got a visitation from relatives for the next few days so things will be a bit 'slow'
Alan
