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 Post subject: Vertical Height Vertical Linearity
PostPosted: Jun Sun 30, 2019 3:05 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 3280
Location: Waukegan, IL
I seem to remember reading that when it comes to adjusting height and linearity, one control only affects one half of the screen, and the other one affects the other half. if thats true, i forgot which is which.

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 Post subject: Re: Vertical Height Vertical Linearity
PostPosted: Jun Sun 30, 2019 5:21 am 
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Location: Oxford, MI
I have been working on the picture adjustments for my RCA 21-S-510 and what you describe is correct as far as this model is concerned, but may not be the same on all televisions.

Adjusting the height control affects the bottom half of the screen more and the vertical linearity control affects the top half more so. a significant adjustment of either also requires adjusting the vertical hold.

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 Post subject: Re: Vertical Height Vertical Linearity
PostPosted: Jun Sun 30, 2019 8:55 pm 
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Location: St. Louis, MO
I just finished working on an Admiral 12x12 that had issues with the vertical linearity.

After a lot of experimentation, I found that it worked better to watch the waveform on the vertical output tube while adjusting the vertical linearity. Vertical linearity, vertical sync, and height interacted a fair bit. It worked much better to set the linearity by oscilloscope and then adjust the other two controls. More experienced restorers may have a different approach, but this was the only way I was able to achieve a good adjustment on my set

Roger


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 Post subject: Re: Vertical Height Vertical Linearity
PostPosted: Jul Mon 01, 2019 1:31 am 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: Waukegan, IL
I had the scope out once and set the vertical watching the vertical output waveforms. set it better i thought than just using a pattern to set it to. guess ill have to do it that way.

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 Post subject: Re: Vertical Height Vertical Linearity
PostPosted: Jul Mon 01, 2019 3:56 am 
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Posts: 27713
Location: Detroit, MI USA
Nearly all the professional techs I worked with did it by eye, very rarely was a pattern generator used. On many older black and white sets with a wirewound control in the vertical output cathode circuit, that was the linearity adjustment and the control in the plate circuit of the oscillator was the height. There is considerable interaction and often the centering had to be changed to get the most linear picture within the viewing area on the screen.

But the circuit positions of vertical controls varies greatly by design and the control might be called one thing in one brand and something else in another brand.

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 Post subject: Re: Vertical Height Vertical Linearity
PostPosted: Jul Mon 01, 2019 8:29 am 
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Joined: May Sun 07, 2017 11:35 am
Posts: 570
Location: Belrose, NSW, Australia
For what it's worth, guys, the reason for the interaction is the fact that the output stage needs to accept a voltage source and convert it into a current source. Classic US design used the slope of the tube to do this, by varying the tube's bias. Of course, the drive waveform also affects the bias and the bias affects the gain, and the "height" control affects the rate of charge of the sawtooth cap and so the free-running frequency of the oscillator. This is the nature of simple circuits.

What HMV in Australia used to do with all their tube designs was to add a small transformer wired as a current to voltage converter, in series with the yoke. This fed back a voltage in series with the sawtooth cap and completely avoided the need for a vertical linearity control - linearity was automatically perfect at any height setting because of the current sensing negative feedback. When I was training TV techs, though, they had a lot of trouble understanding this unusual, but not significantly more complex and very effective, circuit.

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