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Vintage Television and Video Vintage television and video equipment, programmes, VCRs etc. |
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23rd Sep 2019, 12:18 pm | #21 |
Dekatron
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Re: Bush TV22 with TC184 B3 converter.
Time for another set of 3 diodes + 3 caps?
Peter Last edited by peter_scott; 23rd Sep 2019 at 12:32 pm. |
23rd Sep 2019, 12:23 pm | #22 |
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Re: Bush TV22 with TC184 B3 converter.
"Time for another set of 3 diodes + 3 caps"
Hi Peter, I was thinking the same thing. DFWB. |
23rd Sep 2019, 1:25 pm | #23 |
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Re: Bush TV22 with TC184 B3 converter.
Hi David,
Sorry, it was 3 diodes + 2 caps. The configuration Jac sent me that I copied was as below. With my shorted overwind still in place I got about 3.5 kV but with winding gone that is now 7kV. Peter Last edited by peter_scott; 23rd Sep 2019 at 1:33 pm. |
23rd Sep 2019, 1:42 pm | #24 | |
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Re: Bush TV22 with TC184 B3 converter.
Quote:
The old pitch dries, shrinks in volume and cracks. The crevices allow atmospheric water vapor to enter the windings. This is only transiently helped by heating it, by running current through the winding or other methods. The vapor re-enters later of course via the same defects that allowed it to enter in the first place. The only way the transformer can be restored to reliable failure free operation, without a rewind is by the method I have previously posted. The transformer must be placed in a mineral turpentine bath for at least one week. This completely dissolves the pitch and the turpentine infiltrates the windings. Once the pitch is dissolved away the transformer is left to superficially dry, though some turpentine remains deep in the windings. But this is also the solvent for the varnish ( I simply use marine grade spar varnish but transformer varnish is fine) as well, so when the transformer is dipped preferably about 10 to 15 times after some intermediate drying, to build up a thick outer coat, the residual turpentine assists the infiltration of diluted varnish into the windings. Once dry, the transformer windings are both water and water vapor proof and the varnish has a very high dielectric strength. (see attached photo). This way failure is avoided. If mineral turpentine is not available in your locality choose the closest match hydrocarbon solvent and check it also doubles as a solvent for the varnish. (Of course this idea did not come out of thin air, it is borrowed from the processing of tissue specimens for histological slides. Since tissues contain predominantly water, it must be displaced with a non polar hydrocarbon solvent , so later a higher molecular weight wax like substances can replace it in steps after that, before the tissue block is stablized to a solid to be sliced by a microtome (knife). It just turned out that this basic idea was perfect to solve the water ingress problems of old pitch coated line output and other transformers that are pitch coated). It seems too few have taken my advice and the TV22 transformers are still dropping off like flies. |
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23rd Sep 2019, 3:40 pm | #25 | |
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Re: Bush TV22 with TC184 B3 converter.
Quote:
Peter |
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23rd Sep 2019, 3:54 pm | #26 |
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Re: Bush TV22 with TC184 B3 converter.
Before the line output transformer is condemned there are other components in the line output stage that might have caused the low EHT condition.
The set didn't go faulty while in use. DFWB. |
23rd Sep 2019, 4:49 pm | #27 |
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Re: Bush TV22 with TC184 B3 converter.
It's a problem with these old tellies that have been in storage for so many years.
I think it is the old interleaving tissue that decomposes with moisture resulting in breakdown between the windings. Some times you can be lucky. It may have broken down whilst warming up on first switched on after a pause. I have a TV22 that has seen very little service. Something tells me it was disconnected after each rare viewing session and then put away in a cupboard till allowed out for special treats. It looked brand new when I first acquired it. The lopt is the only one I have seen that appeared as new with a clean shiny pitch overwind, usually they are a baked mess but oddly they usually work! After a cap blitz it performed superbly for around 6 hours then the primary section went S/C between the isolated windings. Mike Barker rewound it and it has performed faultlessly since. Thank you for the invitation David but I'm not joining the Bush TV22 society. It would no doubt finally prove to my neighbours that I am completely potty especially when I visit the local village shop wearing a HIRED Dalek outfit. Hope you get it solved. John. |
23rd Sep 2019, 5:25 pm | #28 |
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Re: Bush TV22 with TC184 B3 converter.
"Thank you for the invitation David but I'm not joining the Bush TV22 society. It would no doubt finally prove to my neighbours that I am completely potty especially when I visit the local village shop wearing a HIRED Dalek outfit. Hope you get it solved." John.
Hi John, Then how about a TV12 or better still a TV32? DFWB. |
23rd Sep 2019, 7:43 pm | #29 |
Nonode
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Re: Bush TV22 with TC184 B3 converter.
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23rd Sep 2019, 7:56 pm | #30 |
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Re: Bush TV22 with TC184 B3 converter.
Just had a quick look at my 32 that hasn't had any use in the last few years. Looks like it might need a yellow cap in the frame TB and there's some instability in the width but the alignment is miles better than the 22 had.
Peter |
23rd Sep 2019, 10:22 pm | #31 | |
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Re: Bush TV22 with TC184 B3 converter.
Quote:
However when I first saw the lopty in my Bush, I could see immediately that it should not be powered at all with the degraded pitch coating, that condemns the transformer to failure. So I did not power mine and risk damage before the problem was solved. It is common sense, but it requires patience. One problem when vintage TV's are acquired the owner is enthusiastic to power them to see if they work ,or one argument, to test the CRT. It should never be done unless a minimum amount of restoration work is completed first. This includes assessing the condition of the lopty and its insulation, because that is one of the most difficult parts to repair/rewind. Likely, most of the time these loptys are initially undamaged. But especially in the case of a pitch coating, just in an unsuitable condition to support the very high voltages due to the old cracked pitch and moisture ingress. They are just set up for damage & failure, sometime after the enthusiastic owner powers them. The same is true of the electroltyic capacitors of course and the waxies and these should be dealt with too prior to powering the set, however the approach many use is to power and wait to see what fails, but of course that can take out other components that might be more difficult to replace. So the same principles apply. There may be a number of TV 22's that appear to be running still with pitch coated loptys. If they are used frequently enough, and the transformer is dry enough on the average and the pitch not grossly degraded, they may appear to be working ok, but they won't last and are heading for failure. The idea to build up the thick coating of varnish as a method to protect the overwind and other windings was taken from an early 1960's vintage Marconi studio monitor, this was the method they used in a monitor which supported about 14kV EHT. It was the better solution I had seen to methods prior to that. Other reliable methods that followed involved potting the entire overwind or lopty in polyester resin, but of course this is impractical for something like the Bush's lopty. Other methods have included various types of waxes, but these are not long lasting. Earlier designs were in a canister with oil or wax and like an auto ignition coil, this afforded considerable protection for the windings. Last edited by Argus25; 23rd Sep 2019 at 10:28 pm. |
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23rd Sep 2019, 10:42 pm | #32 | |
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Re: Bush TV22 with TC184 B3 converter.
Quote:
Luckily I purchased a very rough TV24 for very little, the LOPT was left cooking for a week on my bench PSU before fitting it, After many hours of use it continues to work perfectly! It must be remembered that the LOPT was not very reliable when these sets were in production. I would like to see if a modern LOPT from a portable set could be made to work in this chassis... Mark |
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23rd Sep 2019, 11:06 pm | #33 | |
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Re: Bush TV22 with TC184 B3 converter.
Quote:
On my transformer I could easily see cracks extending down to the winding surfaces. On a low voltage transformer, you can get away with this, but not a lopty. When I joined the forum I was horrified to see some people had attempted to remove the pitch by melting it off. With old pitch, heating it does not cause it to flow and melt away easily at all, it tends to bake it on. Also picking at the hard pitch simply damages the windings. To be perfectly fair though the reason I had known about the pitch issue is that I have been restoring valve equipment since the early 1970's and working with pitch coated components. It was a very common method to protect transformers in the Antipodes for humidity protection. I made the same mistakes back then myself , initially trying to melt it, trying to deal with it and found it was better dissolved. I fell into every possible restoration pothole made many mistakes and had to crawl out of it somehow. It has taken many decades to settle on techniques that work and are reliable and give very long term stable outcomes for restoration of TV's. But of course it is still anecdotal experience and any suggestions for a solution to a particular issue might be taken with a grain of salt by others. Also, it seems a human trait that we have to fall on our face ourselves at least once for each problem, before we really learn the lesson and avoid the problem the next time. Last edited by Argus25; 23rd Sep 2019 at 11:14 pm. Reason: typo |
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23rd Sep 2019, 11:20 pm | #34 |
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Re: Bush TV22 with TC184 B3 converter.
I certainly agree that heating & picking off the pitch does pose a danger of damage to the windings.
I like your idea of dissolving the pitch, I have a spare (duff) LOPT from a TV22 so will give it a try. Mark |
23rd Sep 2019, 11:59 pm | #35 |
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Re: Bush TV22 with TC184 B3 converter.
Be patient with it, over a few days to a week, change the bath a few times so you can see what is happening. Try to avoid trying to touch the pitch surface, though a very soft small artists brush can speed things a little, but there is really no need to touch the surfaces. You will know when its basically done, as once nearly all the pitch is gone, the bath will stay nearly perfectly clear over a day, rather than dark brown. Once it gets going the process appears to speed up, because the outer layers of the pitch are more resistant to dissolving than the deeper parts of it.
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24th Sep 2019, 10:10 am | #36 | |
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Re: Bush TV22 with TC184 B3 converter.
Quote:
This would be an ideal guinea pig to try your method, I could then try passing a current through it for a few days and testing it before sealing it in varnish. Mark |
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24th Sep 2019, 10:12 am | #37 |
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Re: Bush TV22 with TC184 B3 converter.
More likely just damp but it will need a long slow dry out.
Peter |
24th Sep 2019, 12:34 pm | #38 |
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Re: Bush TV22 with TC184 B3 converter.
Another News Flash! The line output transformer is OK and the low EHT fault was caused by the 4mfd boost capacitor having gone low capacity. It and the 2mfd scan coil coupling capacitor were replaced this morning. The latter replaced by a non polarised capacitor.
DFWB. |
24th Sep 2019, 12:45 pm | #39 |
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Re: Bush TV22 with TC184 B3 converter.
I used RS Anti-Corona laquer (https://uk.rs-online.com/web/p/elect...quers/1368542/) on my TV22 LOPT after having removed the pitch using white spirit (see https://www.vintage-radio.net/forum/...d.php?t=143229 ). Still OK so far...
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24th Sep 2019, 12:45 pm | #40 |
Nonode
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Re: Bush TV22 with TC184 B3 converter.
That was lucky! Nice bright picture on it too, what CRT is in yours? Is it a 22-16 or a 22-18? Regards Lloyd |