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Vintage Television and Video Vintage television and video equipment, programmes, VCRs etc.

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Old 17th Sep 2007, 8:52 pm   #1
Hunts smoothing bomb
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Default TV24 Help required please

Hi everone,

I have been fiddling for ages with this set and despite what others here have told me, I cannot find the device on the tube neck for centring the picture.

I have included pictures so you can see how bad it is: also one of the back so some kind soul can point me in the right direction

Also whilst I'm here, I cannot get any definition on the finest frequency gratings; in fact you can't see much definition in the second from last: any pointers as to what to adjust and how?

Lastly, I think I have shorted turns in the deflection coils as the raster bottom is not level but the raster top is

So, if anyone has a known good deflection yoke they want to sell me, then I would be very pleased.

Many thanks
Lee
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Old 17th Sep 2007, 9:23 pm   #2
Steve_P
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Default Re: TV24 Help required please

The lever that goes out to the back of the set is focus. The small one further back is for Picture Centring.

http://www.oldtellys.co.uk/otindex.html and select Monochrome Tubes. There's a diagram half way down. You should be able to see the control here. Watch the screen and tweak. There are permanent magnets controlled here and they sometimes slip, so whip the tube neck parts off (carefully!!) and have a look.

The gratings - do a full IF/RF Alignment and see if this improves it. Then check any caps you haven't changed.

Cheers,

Steve P
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Old 17th Sep 2007, 9:44 pm   #3
Ian - G4JQT
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Default Re: TV24 Help required please

Lee,

If your magnets are not the same as those in the diagram in the link from Steve P's posting above, try this: On the circular brass plate of your photograph, there are three 4BA nuts with spring lockwashers. These nuts are at 1 o'clock, 5 o'clock and 9 o'clock. Loosen them a little.

There are two screws on the same plate in oval cut-outs located at 3 o'clock and 6 o'clock. These adjust the left-right/up-down positioning.

Adjust these with a screwdriver - they just go round and round in their mountings in an oval movement.

When you have centred the picture, slightly retighten the locking nuts. Refocus the picture if necessary; adjust the ion trap (the metal ring just in front of the tube base - the screw to loosen is underneath in your example) for brightest and/or best focus in turn with the focussing lever.

When you are happy with the picture, gently retighten the three nuts and the ion trap. They all interact so have a bit of a play before you finally tighten (not too firmly!) everything back up.

The second from last frequency grating is not very clear on this set anyway I don't think. Don't forget the limitations of the converter/modulator as this also plays a part in the final definition. If you can only just about make out the penultimate frequency gratings, that's probably the best you can do. The highest will not be visible on most sets.

Not sure about the effect of a shorted turn, others may be better able to advise. My hunch is that if it were shorted turn(s) it would be worse than that. Does the distortion change slightly when you move those new leads around that go to the frame coils?

Ian

Last edited by Ian - G4JQT; 17th Sep 2007 at 10:13 pm.
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Old 18th Sep 2007, 10:28 pm   #4
Hunts smoothing bomb
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Default Re: TV24 Help required please

Thank you for your replies!
Indeed, Ian, my set has the centring system that you have mentioned. I have not tried the adjustments yet but can see clearly the nuts/bolts and spring washers. Many thanks!
I will report my efforts.

Thanks again
Lee
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Old 19th Sep 2007, 8:53 am   #5
Ian - G4JQT
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Default Re: TV24 Help required please

Lee,

Glad that it's the same as mine - there are differnces between the MK I, II and A.

Settings of focus, ion trap and brightness to some extent all shift the picture around slightly, so the final centering setting might have to be a bit of a compromise.

I've also set my picture size to very slightly overscan (test card-edge arrow heads just off the screen) so that the edges don't ever show.

Let us know if you cure the curve at the bottom.

Ian
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Old 24th Sep 2007, 8:49 pm   #6
Malcolm Burrell
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Default Re: TV24 Help required please

Actually, the image on the TV24 isn't bad! The previous comments regarding the centring adjustments on the bronze backing plate are correct. The screws can be tight and must be adjusted with care - if you hear the focus magnet grating on the tube neck, stop!

In my youth I ruined dozens of sets while striving for perfection! The slight displacement of the lower portion of the test card isn't the result of shorting turns in the scanning coils. It is almost certainly the result of their assembly. That was the result of mass production. Another set of coils might be an improvement but there might be distortion elsewhere. These sets were made to a budget and on the assumption that the viewer was going to watch Muffin the Mule instead of the test card!

As to definition, most of these sets should just about display the 2.5MHz bars (4th set on left) on Test Card 'C'. An exceptional receiver might faintly show the 3MHz bars (5th set on left) on a broadcast transmission. However, unless using the 'NTSC' version of the Aurora standards converter, the highest video frequencies are attenuated to remove any residue of the colour sub-carrier. A good picture resolving 2MHz is preferable to one badly resolving higher definition with 'ringing' etc.
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