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  #91  
Old 06-20-2018, 09:34 AM
old_coot88 old_coot88 is offline
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Phil you da man.
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  #92  
Old 06-20-2018, 11:29 AM
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Wow, lookin good!

Do you intend to experiment with other values of R-86 to address the slight crushing that you observe?

jr
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  #93  
Old 06-20-2018, 11:52 AM
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Always great when black magic turns into problem solved!
Looking very watchable!
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  #94  
Old 06-20-2018, 12:52 PM
old_coot88 old_coot88 is offline
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...rare as rocking horse poo.
Gotta 'member that one.
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  #95  
Old 06-20-2018, 12:58 PM
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Originally Posted by jr_tech View Post
Do you intend to experiment with other values of R-86 to address the slight crushing that you observe?
Unfortunately, I don't have an assortment of 25-watt resistors on hand. I had to mail-order the replacement that I used.

The symmetrical edge crushing is slight, but noticeable with a test pattern. In a crosshatch pattern, the edge-most two or three columns of squares are narrower than the rest.

Any guess as to what range of values might be reasonable to experiment with? The stock resistor is 7.5K. One local store sells 25-watt resistors in values as high as 5.6K. For an experiment, I can wire resistors in series to make other values, of course.

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Last edited by Phil Nelson; 06-20-2018 at 01:02 PM.
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  #96  
Old 06-20-2018, 01:13 PM
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Does the .25 cap affect both overall size and the edge squeeze? If I follow what's happening, will you need a joint adjustment of the cap and the resistor for best overall result?
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  #97  
Old 06-20-2018, 01:25 PM
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I didn't keep a library of screen photos while testing, but I believe changing the .25 cap value did affect the squeeze somewhat, to a lesser extent than the width.

Experimenting with both the cap and resistor values is a possibility, if I get a little assortment of 25-watt resistors to play with.

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  #98  
Old 06-20-2018, 01:57 PM
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For a quick test you could bridge the 7.5k with a much lower wattage resistor, perhaps starting with something like 20 to 50k and observe the change (if any). Also a lower wattage resistor, something like 500 to 1000 ohms could be added in series for a quick test.

jr
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  #99  
Old 06-20-2018, 03:09 PM
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You can't do it with the high wattage components, but if it were lower power, simultaneous adjustment with both a capacitor decade box and a resistor decade box could make short work of a problem like this.

This has been deprecated in the past as "dec-box engineering" because there is no pre-calculation of the correct values. But it need not be looked down on if two things are true:
1) You already have a reasonable starting point
2) You are observant enough to understand which aspect of performance is changing as you make the adjustment.

In a hypothetical example, you might note that a small resistor change modifies overall width (and is it larger or smaller) without much change in edge compression, while the cap affects both width and compression, and adjust first the cap in a small step to get better edges, then the resistor in a compensating small step to get the right width, and so on.

NOTE: you also have to be aware whether the transient condition of an open circuit while switching the dec box could cause a destructive fault. In your case, you already know nothing is being destroyed even with the components open-circuited.
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Last edited by old_tv_nut; 06-20-2018 at 03:12 PM.
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  #100  
Old 06-20-2018, 10:37 PM
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Phil, it might be worth trying the old "seven seconds off & back on" test. Does the raster come back at full width, or is it slow filling out? If unusually slow, are there any peculiarities with the lin during fill-out?
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  #101  
Old 06-21-2018, 10:52 AM
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Phil, it might be worth trying the old "seven seconds off & back on" test. Does the raster come back at full width, or is it slow filling out? If unusually slow, are there any peculiarities with the lin during fill-out?
This is interesting to me. Does slow recovery point to weak tubes or other things as well?
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  #102  
Old 06-21-2018, 11:50 AM
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This is interesting to me. Does slow recovery point to weak tubes or other things as well?
Exactly. It's an old 'quick & dirty' field test for borderline-weak tubes like hor osc and 3.58 osc. (slow achieving sync), hor. out (slow fill-out), vert. out (slow fill-out), RF amp (slow clearing snow), etc.

Same principle as the Life Test on a tube tester which drops the heater voltage down.

This was followed by the 'tap test' of each tube to show up any arcing (like the damper), intermittent shorts etc.

Made service calls more effective with less chance of call-backs.
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  #103  
Old 06-21-2018, 02:20 PM
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OK, I'll try the seven-second test later today and observe the results.

I spent some time yesterday playing with different values for R86, using a handful of 25-watt resistors that I picked up locally. It is a cumbersome and very slow process, to clip a resistor (or series-ed resistors) into place, slide the chassis back into position, turn the set back on, observe the result, and try to compare the pattern to what you saw before. I tried taking photos with the camera on a tripod, and noting the resistor values for later comparison.

Subbing the capacitor values was so much easier with a decade box, where I could keep my eyes on the screen and flip between different values, back and forth, looking at different parts of the screen, etc.

Anyway, yesterday's results were not very informative. When I put a crosshatch pattern back on, I realized that the linearity wasn't quite as good as I remembered.

I also realized that I had begun with the TV in a somewhat random state -- that is, with the various controls set to produce an image with best horizontal linearity & centering. I had also left in the .22 cap across the width coil. What kind of baseline is that? Perhaps it would make more sense to remove that .22 cap and center ALL of the pertinent controls, then repeat the rigamarole of subbing the cap and resistor values, looking for changes that make sense.

There are lots of variables in this equation. In addition to the horiz width and linearity adjusters, you have the horiz centering and horiz drive adjusters, all of which affect width and linearity to some extent. Not to mention the mechanical centering adjusters on the optical box.

Does anyone have a clear idea what changes you would expect to see on a perfectly-linear set when changing the value of this damper resistor (R86)?

Phil Nelson
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  #104  
Old 06-21-2018, 05:49 PM
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Quote:
Originally Posted by Phil Nelson View Post

Does anyone have a clear idea what changes you would expect to see on a perfectly-linear set when changing the value of this damper resistor (R86)?

Phil Nelson
On a perfectly linear set no. I did mess with that and parallel capacitance on a Hoffman that had width and linearity issues a year or two ago.

Some sets that used that big damper resistor (RCA 630?) had taps on the resistor to rough in one of the horizontal adjustments (forget if it was the width or lin) so the control of that name would be in the correct range to work.
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  #105  
Old 06-21-2018, 11:57 PM
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Originally Posted by Electronic M View Post
Some sets that used that big damper resistor (RCA 630?) had taps on the resistor to rough in one of the horizontal adjustments (forget if it was the width or lin)
Yes, now I recall seeing a tapped damper resistor in one of my old TV books.

The 630TS factory manual says this is a coarse linearity adjustment:

"If repeated adjustments of drive, width, and linearity fail to give proper linearity, it may be necessary to move the tap on R209, which is located in the high voltage compartment. Adjustments of drive, width, and linearity must then be repeated."

The parts list describes R209 as:

"Wire wound resistor, 5300 ohms, 20 watt; 500 ohms, 2 watt; and 500 ohms, 2 watt."

Not sure what to make of that description. Why only 2 watts for the 500-ohm segments?

In the schematic, that resistor is drawn with three taps, and the default connection made at the center tap. I interpreted this to mean it's a 5300-ohm resistor, which you can adjust to either 5800 or 4800 ohms by moving the tap. Am I guessing wrong about the resistor construction?

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