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

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Old 6th May 2009, 12:48 pm   #21
dominicbeesley
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Location: Hebden Bridge, West Yorkshire, UK.
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Default Re: Homebrew field / line coils

Thanks for all this info Victor, I have to admit that much of it is above my head at the moment but I will keep plugging away!

If using coils as you suggest above would the drive wave forms just be (roughly) a square wave then the capacitor and saturated inductor add some kind of tilt to make the scan linear?

I'll dig out some old "Radio and Television Servicing" and try and work out what is going on with these! For now I'm off on my holidays so probably won't be able to reply to any messages for two weeks - though I'll no doubt be tracing out circuits in the sand with my toe!

I wonder if they have lots of 1950's NTSC sets still kicking about in Cuba like the big old 1950's cars....try sneaking one of them back in the luggage!

Dom
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Old 7th May 2009, 6:41 am   #22
ENGLISH VICTOR
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Default Re: Homebrew field / line coils

Hi Dom, the saturated reactor works as follows: the reactor, essentialy a ferrite rod cored coil has in near proximity to it a magnet so adjusted that it saturates the ferrite when the last part of the scan current begins to become non linear, this is due to the rsistive component of the yoke, transformer and transfer characteristic of the output valve. The right hand edge of the screen becomes cramped. As the ferrite becomes saturated the inductance of the coil becomes lower thus stretching out the picture width. The reactor is connected in series with the line coils and consits of between 30 and 100 turns typicaly depending on the yoke impedance. The s correction capacitor corrects for the crt screen shape, it being partialy rounded, also some correction is required because the centre of deflection varies with the distance from the tube centre.
I would just save the posts you have and refer to them when you are ready, good luck.
The waveform idealy should be a square wave but with a scan to flyback ratio of about 5:1. (simplified)
Victor.
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Old 7th May 2009, 12:37 pm   #23
KeithsTV
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Default Re: Homebrew field / line coils

Hi Dom

I've found a series of articles in Television which describe the operation of a transistor Line output stage and what the function of the main components is. I believe the principle also applies to a valve Line output stage. This may help you in your understanding of the line output stage and also in the re-design for your specific application. I can scan them and post them here if you are interested.

Keith
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