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Old 11th Sep 2011, 5:53 pm   #83
Retired
Heptode
 
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Join Date: Mar 2009
Location: Fenay Bridge, Huddersfield. UK.
Posts: 673
Default Re: Restorers dream part 2 the chassis.

Hi,

Thanks Dom; I've taken your advice and converted an old screwdriver with a well insulated handle into a LOPT earthing tool but had to use a 4.6M 2W resistor as can be seen in the picture I also insulated the blade with rubber tubing for good measure. I found an old mirror and have now set this up so that I can watch the screen. It's amazing how much time these simple tasks take to accomplish.

I did the test as suggested but the U25 is dead. I also spent a lot of time trying to find the 500mA fuse shown in the circuit diagram to no avail; I went over the whole chassis top and underneath; I checked everywhere; I even removed the LOPT cover but the only two fuses I could find were on the outer back rated at 2A and both tested OK. This is now bugging me especially after being so easily caught out with the mains cap. Whilst searching for the fuse I noticed the two pin mains connector at the back of the set but at the moment power is fed directly to the on/off switch; would something so simple cause a problem; all the valves with the exception of U25 are lit up. I'm not taking anything for granted now. I should have checked for voltage on these pins and will do so when I go back into the workshop as one is most likely live and exposed.

Thanks Bill, I've just been back into the workshop to check voltages on 30P4 and think there is a clue here as I can't find a negative voltage on any of the pins. I haven't had time to check pin outs but reading directly from the valve the readings obtained are; Pin 1 93V; Pin 2 0V; Pin 3 No tag; Pin 4 108V; Pin 5 4V; pin 6 111V; Pin 7 0V and Pin 8 6V.

Out of curiosity I also replaced U25 as Jeffrey very kindly supplied a new one with the set; like a fool I managed to break the single wire right at the envelope; I was surprised as it broke so easily; I used a needle file and trimmed the glass back and soldered a new lead on but the valve like the previous U25 remains dead.

I also noticed a weeping 0.1 cap across the end connector of the tube so I replaced this with a new 0.1uF 630V item.

Thanks also Dave; I'll find my mains neon screwdriver tester; I've not used it for years but I'll try everything suggested.

Kind regards, Col.
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