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

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Old 21st Jun 2021, 7:34 am   #101
peter_scott
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Default Re: Baird Garrick

A really neat job.

Peter
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Old 21st Jun 2021, 7:15 pm   #102
Andy - G8MNM
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Default Re: Baird Garrick

i have new CRM92 with mask. Amazing how it has survived. Andy
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Old 23rd Jun 2021, 12:40 am   #103
beery
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Default Re: Baird Garrick

Hi all,
I have attached some pictures to show the changes made to the line timbase.

The first picture shows the modified circuit that the set had when I received it. Note that it has flyback EHT. The transformer was a bad match with too much output and severe distortion to the right hand side of the picture. An inductor had been placed in series with the line coils to reduce the width (relative to the EHT).

The second picture shows the corrected circuit as originally designed.

The third picture shows some of the detritus that was removed. At this point I had already replaced the 1K width control for one with the correct 2K resistance.

The fourth picture shows a 50uF capacitor of the correct type for the line scan coil coupling in this set. It has been re-stuffed.

The fifth picture shows a round cover that I made up to cover the rather unsightly hole (it was roughly cut) that was left after the extra line linearity control was removed.

Cheers
Andy
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Old 23rd Jun 2021, 9:19 am   #104
FERNSEH
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Default Re: Baird Garrick

Hi Andy, regarding the second attachment, the line timebase certainly resembles the Baird T5 circuit. Component values are almost the same.
No sync injection winding on the Garrick transformer.

DFWB.
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Old 2nd Jul 2021, 1:38 am   #105
beery
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Default Re: Baird Garrick

Hi all,
I thought I should post some pictures of the pictures as it were...

It was difficult for me to get the camera square with the screen, but I can tell you that the line linearity is pretty good, much better than it was with the transformer that was in the set when I obtained it.

The first photo shows the picture from the transformer that was in the set.

The second photo shows the picture from the line output transformer that I made up to replace the original one that the set was made with.

You may notice that the frame linearity is poor. I'm not sure why. There is no adjustment for frame linearity (the control that I thought was frame linearity is in fact frame shift). It might be because the scanning assembly is not square on the tube, but is leaning forward somewhat towards the top. It is not easy to adjust, but I will have a play with it at the weekend.

The pictures are contrast heavy. Remeber that in this set, both the cathode and the grid of the CRT have video drive applied to them in a kind of push-pull arrangement. So, lots of contrast, no problem with flyback lines, but when the contrast is reduced to what I would say is a normal level, the sync gets weak. I wonder if it is worth reducing the drive to the CRT grid, whilst keeping the cathode drive as is (which also feeds the sync separator)?

The other two photos show some people engaging in outdoor pursuits. Of course we know that they would be having much more fun indoors fixing old tellies, if only they had the chance to try it

Cheers
Andy
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Old 2nd Jul 2021, 9:01 am   #106
peter_scott
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Default Re: Baird Garrick

Looking at that net, that's totally unacceptable!

EMI say: "A slight amount of frame crushing at the lower end of the picture is standard."

Peter
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