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Old 21st Feb 2021, 7:02 pm   #161
beery
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Default Re: My first telly TV22

Hi Travellingwave,
that's a great picture.

I've had a little look and I don't think I have a TV22 focus magnet here. It will have to wait until restrictions relax. I will look in a couple of other places though just in case. and I will send you a PM if one does turn up.

Anyway, time to enjoy watching it!

Cheers
Andy
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Old 22nd Feb 2021, 6:55 pm   #162
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Hi Andy

Thanks for the offer - any way would you believe it , I got to putting the case back on and guess what dropped out of the case - the focus magnet follower pin. So Im all sorted.

Just getting my raspberry pi sorted as a media player

Then I have to negotiate with SHMBO about where it can live!!
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Old 22nd Feb 2021, 7:41 pm   #163
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Hi Travellingwave,
That was a lucky find!

I hope the negotiations go well. I find that kind of thing much harder than the actual restorations!

Cheers
Andy
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Old 23rd Feb 2021, 9:01 am   #164
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Default Re: My first telly TV22

I have secretly placed it in the dining room - see how long it takes SWMBO to notice!
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Old 23rd Feb 2021, 8:42 pm   #165
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Oh dear
Been giving it a bit of a soak test ( running for and hour or so) and have lost picture , still have audio so presumably heaters are still up. Will have to investigate tomorrow
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Old 24th Feb 2021, 10:02 am   #166
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Default Re: My first telly TV22

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I have secretly placed it in the dining room - see how long it takes SWMBO to notice!
That's a great picture! It has inspired me to start a new thread featuring members' sets in domestic surroundings. Coming soon!

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Old 24th Feb 2021, 10:48 am   #167
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Default Re: My first telly TV22

So got it back on the bench

Looks like the line output stage has died - No line whistle no EY51 heater.

I have checked the voltage at the grid of the PL81 and get -10v wrt chassis - so I take it this means I have line drive - interestingly when I apply my DMM to the grid I seem to get a line whistle coming back (I think) nothing on the screen though - and I can probe and check the EY51 for life at the same time.

I have checked the windings of the LOPT for resistance and they seem somewhere near right though I know this proves nothing much as there coud be a shorted turn.

Any ideas what I can check to prove health of LOPT?

I have a NOS PL81 arrived just this morning.
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Old 24th Feb 2021, 10:50 am   #168
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SWMBO notice it and did not protest too much so I think I got away with it!!
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Old 24th Feb 2021, 10:50 am   #169
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She was more upset by the smell of T cut as I polished up the cabinet
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Old 24th Feb 2021, 10:53 am   #170
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Default Re: My first telly TV22

Were the flowers a peace offering?
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Old 24th Feb 2021, 12:19 pm   #171
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Default Re: My first telly TV22

Flowers were already there!

So there is definately some line whistle coming from the LOPT , but no lif at the EY51 , anode 1 volts on CRT measures 40v using the peak hold function on my DMM (I got 300 volts before)

the line whistle sounds a bit erratic almost as though there may be some sparking going on within the primary of the LOPT. So I'm fearing the worst - but this is always a danger when fault finding.

Any other things I can check??

Thanks
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Old 24th Feb 2021, 1:28 pm   #172
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Default Re: My first telly TV22

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Flowers were already there!

So there is definately some line whistle coming from the LOPT , but no lif at the EY51 , anode 1 volts on CRT measures 40v using the peak hold function on my DMM (I got 300 volts before)

the line whistle sounds a bit erratic almost as though there may be some sparking going on within the primary of the LOPT. So I'm fearing the worst - but this is always a danger when fault finding.

Any other things I can check??

Thanks
Did you varnish the primary in the end?...
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Old 24th Feb 2021, 1:45 pm   #173
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Hi Helder

No I didn't I was a bit worried that if I covered the whole thing in varnish inside the primary that it would not neccesarily get to where it needed to go and would make a hell of a job to dismantle if a fault subsequently occured. SO I just coated the overwind.

I have just checked and I have have about 50 ohms between the primary and secondary of the transformer with it still in circuit - I have read that they often fail with secondary to primary shorts - if I measure in circuit I presume there should be no resistance here?

Looks like lopt is going to have to come out
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Old 24th Feb 2021, 2:30 pm   #174
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Hi Helder

No I didn't I was a bit worried that if I covered the whole thing in varnish inside the primary that it would not neccesarily get to where it needed to go and would make a hell of a job to dismantle if a fault subsequently occured. SO I just coated the overwind.

I have just checked and I have have about 50 ohms between the primary and secondary of the transformer with it still in circuit - I have read that they often fail with secondary to primary shorts - if I measure in circuit I presume there should be no resistance here?

Looks like lopt is going to have to come out
Yes, to my knowledge the primary-secondary shorts are the main cause of failure. The turps + varnish process was described on the forum by Argus25, whose lopt has behaved flawlessly since he varnished it (overwind + primary/sec) many years ago. So it's a one-off restoration, but it should really last. Leaving the primary/secondary without any protection is risky, and there are many more stories of people with shorted primaries (me included) than with problems in varnished lopts (none that I know of). The pattern is the same as in the lopt of my first tv22. it worked well for a few hours before kicking the bucket. So you'll have to get it rewound. You'll probably have to change the 470pF cap after that to get the same / similar behavior (EHT, width, etc.)
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Old 24th Feb 2021, 2:34 pm   #175
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Default Re: My first telly TV22

Well got it out and definately short between primary and secondary - well 30 ohms so near as damn it.
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Old 24th Feb 2021, 2:43 pm   #176
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Default Re: My first telly TV22

How rusty are the laminations?
This can effect the line output transformer enough to cause problems with a self oscillating stage.

A good ECL80 is more important than a good PL81.

Note that once the transformer has failed such as to prevent oscillation, then the PL81 will be biased fully on and this will quickly kill the valve and further damage the transformer.

If you are very lucky then the fault is something simple like failure of one of the two 2uF capacitors, such as the one on the scan coils.

If you find the top deck valves glowing brightly, but some of the rf valves cold, then one of the heater decoupling capacitors on the RF deck has gone short, you can just snip one end as a temporary fix. For some reason this fault sometimes also stops the line time base working.

Have to stop there for the school run!

Cheers
Andy
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Old 24th Feb 2021, 4:23 pm   #177
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Well got it out and definately short between primary and secondary - well 30 ohms so near as damn it.
The issue is down to the same problem with wax paper caps: paper. Old paper becomes yellowed and brittle (unless it's acid-free, which as far as I know was mostly used for artwork, but not for electronics). So unless the insulation is reinforced somehow (and turps + varnishing while still wet definitely does the job) the lopt will likely fail sooner or later, hence my insistence in previous posts.
Anyway, I hope you can get it rewound fast and get the set back up and running. It sure looks great in your room.
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Old 24th Feb 2021, 5:21 pm   #178
Travellingwave
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Default Re: My first telly TV22

Thanks Helder , should have followed your advise more closely.

Any way since it was a very clear primary/secondary short at least I’m not wondering if it’s the LOPt or some other fault.

I have started to carefully dismantle the transformer. I’m inclined to have a go at rewinding it myself , unless people really feel this is a daft idea. I see others have managed it. I am taking very careful notes and pictures as I go so the process can be reversed as closely as possible.

Might even start a little side project in the form of an automatic coil winder

I guess life would be boring if stuff just worked!!
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Old 24th Feb 2021, 5:25 pm   #179
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Inner coil and laminations removed
The laminations have suffered some corrosion and swelling at one end. Good smell of white spirit so Helder right it does get in. As I unwind it will get a better idea how well the spirit has impregnated the paper.
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Old 24th Feb 2021, 6:42 pm   #180
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Default Re: My first telly TV22

Have ordered some double insulated 0.25 mm enabled wire, and some polyester transformer tape, 60 microns thick.

Have also ordered a 4 axis CNC shield for arduino , for next to nout, so a coil winder is def on the cards.
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