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Old 15th Mar 2019, 11:56 am   #41
GreasedMonkey
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Default Re: GEC Junior Fineline project.

Nothing on the spikes as far as I can see.
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Old 15th Mar 2019, 12:09 pm   #42
ms660
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Default Re: GEC Junior Fineline project.

There's a photo in this link showing correction magnets fitted:

https://en.wikipedia.org/wiki/Deflection_yoke

Lawrence.
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Old 15th Mar 2019, 6:08 pm   #43
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Default Re: GEC Junior Fineline project.

Hi GM,
That really looks pretty good in the picture. The picture is very well centred, the only real errors I can see are a slight narrowing of the picture at the top and a slightly wiggly horizontal line at the bottom. You won't correct these errors with the ring magnets.

Most manufacturers would not have been concerned with that minor amount of distortion and most viewers would never have noticed.

These are not broadcast standard monitors and domestic TV's had many shortcomings.

You can download a DVD of proper testcards from this link:

https://www.vintage-radio.net/forum/...ad.php?t=71637

Read through the whole thread as the latest files to download are nearer the end. Of course, you need DVD writing capabilities. At least then you could see the set with a correct aspect ratio testcard.

Hope that helps

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Old 15th Mar 2019, 6:24 pm   #44
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Default Re: GEC Junior Fineline project.

Thanks for the link, i will have a look at that.

I think what bothered me the most about the picture was the fact it was taller on the left than on the right. I watch a lot of subtitles programs and slanty subtitles would have drove me round the bend.

Anyhow, I made some very weak magnets today and did a little experimentation. The addition of a single magnet has improved things a lot. I have a test card I am happy with now. Still not perfect but itís to a point where the imperfections will not be noticeable for tv viewing.

SWMBO says there was nothing wrong wit it before and that I am just being fussy. But I think she just wants it off the kitchen table.
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Old 15th Mar 2019, 6:32 pm   #45
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Default Re: GEC Junior Fineline project.

Very slight rotation of the scan coils would even out those slight discrepancies. TV adjustment is all about minimising the deficiencies in the picture!

Anyway, you will find the wandering black level (when watching a moving picture) far more annoying than slight geometric errors!!

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Nick
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Old 15th Mar 2019, 6:45 pm   #46
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Default Re: GEC Junior Fineline project.

I should have said, I did rotate the coils a tiny bit after taking the photograph.

One step ahead of you on the black level, I have added a diode clamp circuit in the video buffer stage. This may not be an official or approved mod, but it’s my set and I intend to use it so I wanted the picture as good as I could get it. It’s actually a very watchable set now.
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Old 15th Mar 2019, 6:56 pm   #47
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Default Re: GEC Junior Fineline project.

Quote:
One step ahead of you on the black level, I have added a diode clamp circuit in the video buffer stage. This may not be an official or approved mod, but it’s my set and I intend to use it so I wanted the picture as good as I could get it. It’s actually a very watchable set now.
Well done! I'm very much in favour of such mods that make sets more watchable or more reliable. After all we are not constrained by the cost of incorporating 'improvements' like the original manufacturer. Black level clamp mods are now very high on my list!

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Nick
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Old 15th Mar 2019, 7:49 pm   #48
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Default Re: GEC Junior Fineline project.

I see no reason why not to add a simple clamp circuit, component cost is next to nothing and it’s such an easy thing to make.

But, I don’t know if you have read my previous posts, the ultimate aim of this project is to have a single box solution to tv viewing. Now I have a fully functional set with a good picture, I plan to add a freeview receiver PCB. The diode clamp on the video buffer is required for this as the signal out of the freeview card is not even close the the signal the set produces at this stage.

Now I understand this may be a mod too far for many in the vintage TV world. But this is my plan. This evening I will be building a 2 transistor video amplifier to produce the 3V pk-pk Video signal needed. This will also produce the required offset. Replicating the sets own video signal is I think the best way to ensure that all of the pulses and blanking levels are correct. The audio levels from the freeview card are spot on as they are, which is handy.

There will be a small switch somewhere to switch from analogue to digital as I also intend to use this set for watching my old VHS tapes, so the set will still have to function as the factory intended.

I have really enjoyed this project so far and there is a distinct danger that I will be on the hunt for another old TV when this one is finished. The help both from members of this forum and VRat have made the whole thing achievable. So my thanks to everybody who has contributed this far.
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Old 16th Mar 2019, 5:04 pm   #49
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Default Re: GEC Junior Fineline project.

I don't see any problem with your plan - after all this TV will now be used and will be providing a picture better than it was when new! If it were a particularly rare set then the modifications could be made reversible, but that's not really the case here.
I think that if the geometry was way out small magnets of around 1cm square could be put on one or two of the spikes, then rotated to improve matters. However your set would have passed with no correction deemed necessary, I suspect.
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Old Yesterday, 2:30 pm   #50
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Default Re: GEC Junior Fineline project.

Project complete.

I now have a nice little freeview enabled Junior Fineline. Some may say this is sacrilege, but I like it.

Thanks again for all of the help along the way. Its been an enjoyable little project.

Next project I guess is to repair my scope which died half way through.
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Old Yesterday, 6:54 pm   #51
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Default Re: GEC Junior Fineline project.

Looks great! Oddly enough I just picked up an old copy of Television magazine from 1976 ans there was a servicing article on the Fineline in it.
Now fixing your 'scope - that's a challenge!
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