#391
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Biggest thing will be figuring out what's up with the pulse regulator. I was only ever able to get about 5kv out of the flyback, but it didn't burn up either. That says to me it's probably still good, but the regulator was dragging it down. Once you trace that part of the circuit, we'll know more.
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Evolution... |
#392
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I have Fink's other books but not that one. Could you scan the relevant pages? Thanks, Darryl |
#393
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Pete |
#394
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I have also had good luck with early-mid 1930's wet electrolytics. If the electrolyte has not leaked (due to perished rubber seals) I have been able to reform and use these as well. My old Scott radio has a wet electroytic from1935 and it maintains the 20ufd with vitually no leakage. The reforming took about four days incrementally increasing the voltage across the wet electrolytic until the full rated voltage was reached. As the capacitor reforms, the leakage current drops and the wet electolytic leakage remains constant at about 50uA at full voltage. The post WWII dry electrolytics reform pretty fast but I still give each a couple of days to ensure the leakage is below 100uA and remains there. Terry |
#395
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Thanks Pete. That is certainly different than what I expected. The burst is down in the sync rather than riding at the black level. I still need to find out how they phased the burst and components.
Darryl |
Audiokarma |
#396
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I have an article from p338-343 in the March 1953 Proceedings of the I.R.E. where they describe how they generate a CPA NTSC color bar test pattern if that would help. They describe how these signals were used in the late 1951 and 52 tests. The color sync was 3.89 Mc I could email it to you if you think it would help. The files are a little too big to post here. James. |
#397
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Thanks James PM sent |
#398
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Pete |
#399
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Stands to reason the burst should not be on a pedestal then, if issues were encountered. The receiver could be modified to work that way, in the event it was built for the burst being on a pedestal. Circuit mods would likely be minimal.
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Evolution... |
#400
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Nice catch Pete.
From the article it sounds like it was a certain monochrome set that had trouble with the burst being in the sync area, not the CPA set. I'm also getting out of this article that they changed the burst to ride on the black pedestal for NTSC not for the initial CPA. I guess it's easy enough to just make this switchable in the converter Darryl |
Audiokarma |
#401
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Here is a preliminary schematic of the HV regulator circuit:
http://www.earlytelevision.org/image...olor_sweep.pdf |
#402
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The only reason I can think of for putting the burst in the sync region is to prevent it being visible during retrace on some existing receivers without power blanking. But that also means that most existing receivers will see it as a second H sync pulse. I think it's an excellent idea to make this switchable so we can see the effects of one case or the other on the sets at ETF. |
#403
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According to Bernard Loughlin, it was early determined that the burst on the pedestal caused sync instability problems and the pedestal was removed.
Perhaps making it switchable is commendable but I think by the time Nick's prototype was tested the burst pedestal was already just history. Terry |
#404
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the circuit appears to provide a degenerative-pulse bucking arrangement so that when the HV rises, the 6BQ6 reduces the pulse to reel back the HV. Terry |
#405
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Audiokarma |
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