Bush TV22 LOPTX questions

[EF80TVVALVE]

Hi all

I recently picked up a TV22 and decided to take a look at it this weekend. It's obvious that it had a long service life and some of the components suggest it was in use until the late 60s or early 70s. The Lopt pitch has cracked and flaked and there is some rusting on the laminations looking at the top of the Lopt. I haven't tested for continuity yet but the small TX on the side is okay so unless a fault occurred in the set I presume the Lopt will be also.

I'd like to remove the pitch and re-coat the Lopt. I see there are a few threads but can anyone advise me on what they soaked their Lopt in to soften the pitch? or is the heat method better? Also what is best to use to re-seal it once all of the old pitch has been removed?

[peter_scott]

http://www.worldphaco.com/uploads/BUSH_TV22.pdf

[Ed_Dinning]

The heat method will do no harm and is worth trying first.
The EHT overwind is normally pretty reliable, but the innerwindings are not. Rusty lams are not normally a problem, but the blocking osc transformers often go o/c

Ed

[EF80TVVALVE]

Thanks both for the replies. Peter, that is a very informative write up and answers my questions regarding soaking the Lopt. There's also a lot of information there that will be useful further in the restoration so thank you for forwarding that to me.

Ed, I'll give it a continuity test and first make sure everything is okay, if I have any O/C windings then expect a PM from me! It does look relatively good but obviously it could look perfect and still have a fault. I may try the heat method first and see how it goes. Should the pitch be too dry and brittle and I lose confidence then I'll probably go with the white spirits as I wouldn't want to cause any damage.

[Lloyd 1985]

The problem I found with the LOPT from one of my TV22’s was that it failed with the primary and secondary shorting together after a long period of seemingly perfect operation. I had previously removed the pitch with a hot air gun, and cleaned up the laminations to get rid of a lot of rust, the primary/ secondary part had iffy looking insulation from the start, the enamel was quite flaky, I sprayed over it with lacquer, and the set ran really well for a long time, I even displayed it at a vintage show where it played non stop for 8 hours. I really must get round to rewinding it, or give it someone else to rewind!

Regards
Lloyd

[Petedox]

I used the white spirit method, took about 3 days soaking (in a convenient tumbler), with occasional agitation. See before and after below.

After drying for a few days I coated it with transformer varnish. Works fine!

[Petedox]

...also did the same with another TV22 LOPT with horizontal laminations.

[Helder Crespo]

Originally Posted by Petedox

I used the white spirit method, took about 3 days soaking (in a convenient tumbler), with occasional agitation. See before and after below.

After drying for a few days I coated it with transformer varnish. Works fine!

Hi Peter
Your photo shows the soaking of the pitch covered part of the LOPT. Isn't it important to soak the primary/secondary inside the tube, so as to remove its original varnish? Since this is where most failures occur (short between primary and secondary, and not on the EHT overwind). The varnish applied afterwards should also cover the whole LOPT, I believe (except tags, of course).
Best
Helder

[Petedox]

Yes Helder, lopt was inverted every now and then to get a full soaking. Varnish (not shown) was applied to whole structure afterwards.

[Petedox]

This is the varnish I normally use, never had a problem:

https://www.ebay.co.uk/itm/CLEAR-AIR...72.m2749.l2649

[Helder Crespo]

Originally Posted by Petedox

Yes Helder, lopt was inverted every now and then to get a full soaking. Varnish (not shown) was applied to whole structure afterwards.

Thanks for the info Peter.
BTW, do you have any suggestions on how to treat rusty laminations without having to disassemble the whole thing?
Thanks
Helder

[Helder Crespo]

Originally Posted by Petedox

This is the varnish I normally use, never had a problem:

https://www.ebay.co.uk/itm/CLEAR-AIR...72.m2749.l2649

Thanks for the great tip Peter!
This is the least expensive insulating varnish I've seen so far, and its specs appear to be excellent. And your results too! It should be allowed plenty of ventilation due to Xylene (also used in good anti-corona formulations).
Helder

[Petedox]

Hi Helder, I think this has been detailed on the forum in the past. But I don't know of any way of doing it properly without removing the laminations. Once the whole transformer is cleaned up it's not that difficult to remove them, individually clean each strip and reassemble.

[Helder Crespo]

Originally Posted by Petedox

Hi Helder, I think this has been detailed on the forum in the past. But I don't know of any way of doing it properly without removing the laminations. Once the whole transformer is cleaned up it's not that difficult to remove them, individually clean each strip and reassemble.

Yes, you're right. I've seen at least one thread on this, but it involved a complete disassembly. From your experience, can the lams be removed without having to remove the former with the primary and secondary, hence without disturbing the thin wire connections?
Thanks
Helder

[Petedox]

I only removed and cleaned the laminations on the lopt that had horizontal laminations. Can't quite remember the exact process now, but it wasnt that difficult as far as I recall. (You're half way there if you have a nice clean one to start with!)

I didn't need to do it with vertical lam lopt. Possibly it's more difficult.... maybe someone else can advise?

[Petedox]

EF80TVVALVE, A while back I drew this pinout with approx resistances. Should be self explanitory. Maybe of some help?

[EF80TVVALVE]

Thanks all for the advice, I'm going to try and free it over the weekend and inspect it l, then I'll post my findings along with some photos when I've done so. I'll order some of the varnish for when it's ready to have a new finish applied. I'll also have a look to make sure there is continuity on the right points.

Just a question regarding the windings internally (the Lopt on my set has the vertical laminations in the length of the tube), will I also need to get these out of the paxolin tube and varnish/refit too?

[Petedox]

No you shouldnt need to. After cleaning, if the continuity is ok just leave alone!

[Lloyd 1985]

If you do remove them, you'll find they won't all go back in! That's what I found with mine, the rust had made them bigger, I had to scrape the rust off and then varnish them to get them to go back in, I should probably have left them well alone!

Regards,
Lloyd

[Ed_Dinning]

In very serious cases of Lam rust it could split the paxolin tube and the pri windings would go down to ground

Ed