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  #391  
Old 03-27-2012, 09:52 AM
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Quote:
Originally Posted by Steve McVoy View Post
I don't know how much I can get working by the convention. There are lots of cut wires and dangling components. If I can figure out where everything goes I may get most of the set working.

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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  #392  
Old 03-27-2012, 10:26 AM
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Originally Posted by Pete Deksnis View Post
Darryl

Fink, Television Engineering, 1952 edition shows the "color-phase synchronizing pulse" in figure 417 on page 549, which may help.

Pete
Hi Pete,
I have Fink's other books but not that one. Could you scan the relevant pages?

Thanks,
Darryl
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  #393  
Old 03-27-2012, 02:44 PM
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Pete Deksnis Pete Deksnis is offline
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Originally Posted by tubesrule View Post
Hi Pete,
I have Fink's other books but not that one. Could you scan the relevant pages?

Thanks,
Darryl
Here's a photo of the page.

Pete
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File Type: jpg 1951-CPA-color-phase-syncPG.jpg (111.1 KB, 63 views)
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  #394  
Old 03-27-2012, 03:41 PM
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Originally Posted by JBL_1 View Post
Looks to me like there is one newer yellow electrolytic soldered under the chassis.
I'm a big fan of getting rid of all the leaky paper caps. But I have also had very good
luck with electrolyics in cans from the pre-wars up thru the mid 50's. I just reform them with a very low charge current and they are not leaky. It is not like they are in a place to cause a lot of damage when they short. My TRK-120 has all of it's original electrolytics and it works fine.. I thought Harry told me he got it from a picker from the Lancaster area.. I'll have to go back and check my emails.
I am glad to see someone else saving the early dry electrolytics. I reform them as well and have little problem with them.

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
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  #395  
Old 03-27-2012, 07:49 PM
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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
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  #396  
Old 03-27-2012, 09:37 PM
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Originally Posted by tubesrule View Post
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
Darryl,

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.
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  #397  
Old 03-27-2012, 09:43 PM
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Darryl,

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.
Definitely! That sounds like it might contain enough information to fully implement CPA.

Thanks James

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  #398  
Old 03-27-2012, 10:16 PM
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Originally Posted by tubesrule View Post
Thanks Pete. That is certainly different than what I expected. The burst is down in the sync rather than riding at the black level.
Darryl
Here's something from Loughlin published by IEEE in 1984; it seems to explain the odd burst.

Pete
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  #399  
Old 03-27-2012, 11:44 PM
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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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  #400  
Old 03-28-2012, 07:01 AM
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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
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  #401  
Old 03-28-2012, 07:57 AM
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Here is a preliminary schematic of the HV regulator circuit:

http://www.earlytelevision.org/image...olor_sweep.pdf
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  #402  
Old 03-28-2012, 10:20 AM
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Quote:
Originally Posted by tubesrule View Post
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
Darryl,

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.
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  #403  
Old 03-28-2012, 10:48 AM
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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
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  #404  
Old 03-28-2012, 10:56 AM
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Originally Posted by Steve McVoy View Post
Here is a preliminary schematic of the HV regulator circuit:

http://www.earlytelevision.org/image...olor_sweep.pdf
Interesting. Perhaps at this time, practical shunt HV regulation was not yet viable?

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
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  #405  
Old 03-28-2012, 10:58 AM
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Quote:
Originally Posted by tubesrule View Post
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
Note that CPA was NTSC!
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