Quote:
Originally Posted by stevehertz
Re the LOPT, some say pass a small DC current through it, others say remove the pitch etc. Which is best? pros and cons?
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From my experience, removing the pitch with white spirit and dipping in varnish (while still wet from the white spirit) will result in deep impregnation of the varnish in all windings, and not just the overwind. And TV22/TV24 LOPTs are known to fail due to o/c in the primary section. I believe that Ed Dining (who rewinds LOPTs) has posted here that the thin and aged paper insulation can become carbonised, hence causing the problem. Also, if you remove the pitch and recoat, this should prevent water from getting into the windings. I guess that if a set is used regularly it should be fine to just pass a current prior to first use, but a stored "cold" set will eventually gather moisture unless its original and usually cracked (hence non-effective) pitch coating is replaced by either another pitch coating or varnish.
As for the EHT cable, the one in my first set has been replaced for safety during the rewinding of the LOPT, which had developed the dreaded o/c primary after a few hours of steady operation. Prior to that, the original cable and insulation seemed to work fine.