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  #1  
Old 05-30-2018, 09:25 PM
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The originals were 600-volt rated paper caps, which I replaced during the first recapping pass. C64 is .035 and C65 is .05, which look like pretty standard values for those caps in my old TV books.

I replaced them with modern film caps (the brown chiclet style) rated for 630V. I paralleled two caps to make up the .035 cap.

I guess it's possible that one of the replacement caps is bad or that I (shudder!) installed a wrong value. I can disconnect and test them.

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Last edited by Phil Nelson; 05-30-2018 at 09:29 PM.
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Old 05-30-2018, 11:08 PM
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Quote:
Originally Posted by Phil Nelson View Post
The originals were 600-volt rated paper caps, which I replaced during the first recapping pass. C64 is .035 and C65 is .05, which look like pretty standard values for those caps in my old TV books.

I replaced them with modern film caps (the brown chiclet style) rated for 630V. I paralleled two caps to make up the .035 cap.

I guess it's possible that one of the replacement caps is bad or that I (shudder!) installed a wrong value. I can disconnect and test them.

Phil Nelson
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On other sets of the day that were based on the RCA 630 those caps on the linearity coil were 1000V IIRC. Are you sure the 600v ones you found in it were original?
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  #3  
Old 05-30-2018, 11:44 PM
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They are specified as 600V in both the Sams and Riders parts lists, for what that’s worth.

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Old 05-30-2018, 09:42 PM
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I have less confidence that they are the problem, since you replaced them, but it doesn't hurt to double check. There seem to be two things going on: left and right not the same width (usual sort of linearity problem), and sides much wider than the center. I don't understand the circuit well enough to point to a possible cause or causes.

Did you replace C-76 and C-77?
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Old 05-30-2018, 10:28 PM
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C76/C77 are 1000-mfd/15V electrolytics, which I replaced with new 25V-rated electrolytics. All paper & electrolytic caps have been replaced.

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Old 05-31-2018, 12:28 AM
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C76/C77 are 1000-mfd/15V electrolytics, which I replaced with new 25V-rated electrolytics. All paper & electrolytic caps have been replaced.

Phil Nelson
OK, they are just huge filters to bypass all AC. I was guessing that, but wasn't sure if they could be smaller values that could shape the waveform. Never mind.
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Old 06-20-2018, 12:58 AM
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I've been watching this thread with great interest. Very well done. Just goes to show "never give up". Working rear projection sets would have to be as rare as rocking horse poo.
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Old 06-20-2018, 12:52 PM
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...rare as rocking horse poo.
Gotta 'member that one.
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Old 06-20-2018, 04:45 AM
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Very nice work. Interesting to see how these sets performed. They must've really impressed people back then with their, for the time, huge picture.
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Old 06-20-2018, 09:34 AM
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Phil you da man.
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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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  #12  
Old 06-20-2018, 12:58 PM
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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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  #13  
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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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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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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