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Old 2nd Aug 2011, 8:22 pm   #34
TriMan66
Pentode
 
Join Date: Jun 2009
Location: Royston
Posts: 116
Default Re: Help with a HMV TV

Hi,
So I took some more measurements whilst the set was in its "warm up phase". It takes 1 hour 5 minutes to get the boost volts up from 450V to 650V. This is consistent over serveral times watching the TV. I'm having great fun watching the original Pink Panther series again!
The grid drive to the EL36 (6CM5) shown in post #1 is rock steady at -150V instead of -170V. Sheild volts are 171V instead of 150V but don't change during the one hour.
Cathode volts should be 0.14V and are 0.15V and don't change.
HT1 should be 240V and is 244V.
HT2 should be 215V and is 221V.
Neither of these change during the hour.
So I assume the drive to the LOPT is OK.
The pin 3 volts to the picture tube should be 400V and does vary from 290V to 350V, but since this is derived from the boost volts this is not surprising.
It is interesting that whilst measuring this, the contrast on the picture significanlty improves.
Since the LOPT was tried and was working previously, although not out of suspission, is unlikely to be the culprit.
I may try a different selection of valves.
I'm also wondering if there is something loading the boost volts, causing this issue.
regards
Craig
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