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Murphy V849U ( Includes the RBM LOPT Overwind Cure)

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Katie Bush
(@katie-bush)
Illustrious V-Ratter Moderator

Good point Chris. I'd never heard of Kapton tape before. I'll follow the link and invest in some.

Many thanks!
Steve

Same here! :aak :aad

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Posted : 30/11/2015 8:36 pm
crustytv
(@crustytv)
Vrat Founder Admin

I've made Andrews thread a sticky as it contains the cure for the dreaded Bush LOPT fault. I've also amended the thread title to reflect the LOPT cure info contain within this Murphy repair thread.

What's even better is we now have a further evidence that his method is a working solution. David has followed Andrews advice and it appears to have also now cured his failing TV115 LOPT .

Well done Andrew on a superb solution.

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Posted : 12/04/2016 11:33 pm
colourstar
(@colourstar)
Honorable V-Ratter Registered

That's great news about David's set. As far as my own ailing Murphy LOPT goes, I can muster 30v from a Farnell bench PSU but although this does make the overwind good and warm, it's some way off being hot enough to ease it apart. Andrew did his with 35v across it, so I'm just that little bit short of volts!

Steve

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Posted : 13/04/2016 12:12 am
PYE625
(@pye625)
Famed V-Ratter Registered

That's great news about David's set. As far as my own ailing Murphy LOPT goes, I can muster 30v from a Farnell bench PSU but although this does make the overwind good and warm, it's some way off being hot enough to ease it apart. Andrew did his with 35v across it, so I'm just that little bit short of volts!

Steve

30 volts should do it Steve, may take a little longer, but you'll know when you can feel slight movement of the overwind. :qq1
PS, my Murphy LOPT is still holding out after all this time so I can confidently say it does cure the problem.

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Topic starter Posted : 13/04/2016 9:53 am
colourstar
(@colourstar)
Honorable V-Ratter Registered

Thanks Andrew, that certainly gives me hope! I'll leave it on a long simmer and see if there's any movement.

Steve

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Posted : 13/04/2016 10:05 pm
davidh1041
(@davidh1041)
Busy V-Ratter Registered

Steve, i used my 30 volt bench supply to cook the overwind, i had removed it from the former. I left it for a couple of hours and it softened up enough to carefully extract the tuning coil. I then carefully removed any lumps of tar in and around the core. Then wrap as many turns of tape around the coil so that it fits nice and snugly back into the core of the overwind. Its well worth the trouble, my TV115 seemed ok to start with using the tripler, but the primary ran hot. Since replacing the overwind, both primary and overwind run luke warm, (i think some of the heat is radiation from the PL36) and the set now has a lot more available width.
Good luck. David

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Posted : 14/04/2016 10:39 pm
colourstar
(@colourstar)
Honorable V-Ratter Registered

Success! :bba

It was a bit of a battle but after 3+ hours at 30v and a fair bit of squeezing/manipulating the warm overwind to break it's grip, the inner coil came out. A plastic solder dispenser tube was exactly the same diameter as the coil former and I used that to push it out through the overwind. It is wrapped in fabric tape just as the other examples have been.

Just need to order some Kapton tape now, then we'll see how things progress.

I'll keep you posted.

Steve

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Posted : 15/04/2016 12:06 am
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