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  #16  
Old 03-02-2017, 11:07 PM
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Could the HV rectifier tube just be bad?
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  #17  
Old 03-04-2017, 08:12 PM
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  #18  
Old 03-05-2017, 06:37 AM
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This problem has been written about several times on here, and a few
other message boards. Go to the Big "G" and search for stuff like
"Zenith 6HV5 high voltage regulator" And you know add a few words,
change a few "hv reg" "problem" etc. you will find links and some
areas that were explored. A few years ago Doug had a problem with one
and he replaced the VDR I believe it's R271 on your circuit. Others
don't seem to have posted a solution.

Some also refer to bad HV adjustment control pot, but symptoms seem to
match yours so that circuit is probably where your problem is, and
possibly not the picture tube. There are a few pages of postings.
Naturally you have more than just the VDR to look at, Caps, bad
resistors, etc.

Good Luck.

https://www.google.com/#q=zenith+6HV...ator+circuit&*


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  #19  
Old 03-05-2017, 11:31 AM
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Interesting albeit simple thing to note on this TV--For years I used a zenith 19cc19 as a daily watcher. That is a 4 tube hybrid chassis. Anyway one day I switched it on and it came up with a huge picture like you noted. Also bad focus etc. Upon measuring anode volts and checking the horiz ckt, I noticed the HV adjustment pot. It was as simple as that...the thing had dead spots in one part of its rotation. I didn't dare clean it, but replaced it with a Coilcraft part and it has been rock solid ever since
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  #20  
Old 03-07-2017, 01:45 PM
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Check the resistance on the HV adjust pot. My 25CC50 daily watcher developed intermittently unstable HV a couple years ago, different HV reg circuit with 2 VDRs and 6JH5 pulse regulator, but same 3 Meg HV pot feeding the regulator grid. It turned out that the HV-adj pot had drifted up to about 6 Megs. Probably couldn't source enough grid current to the regulator. Also, if you find you can't adjust the HV to spec, check the 5% resistors in the regulator, they need to be close to correct value.
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  #21  
Old 03-07-2017, 02:26 PM
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I'm planning to get back on this soon. Last weekend was busy. I need to check all the resistors, and caps with my heathkit C3, and component tester.
One thing that slowed me down is a TV repair book I have that contained a GREAT explanation of the Zenith HV reg. circuit has vanished...I forget how it is supposed to work...I feel like I could do a better job fixing it if I understood it.
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  #22  
Old 03-07-2017, 06:05 PM
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For info on troubleshooting a Zenith Pulse HV Regulator Circuit, Zenith Training Seminars from 1969 and 1970 have the gouge, but without....

PF Reporter june 1969
sep 1972
nov 1974

are your best bets:

http://www.americanradiohistory.com/...om_per_page=10
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  #23  
Old 03-08-2017, 10:19 PM
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Problem solved.

One of the first things I did over a week ago was replace the dud HV rect with a NOS one that tested good...

Today I tried running the set with the Reg pulled, but ONLY it's heater connected, jumpering the HV reg cathode diodes, and shorting the ground side HV pot resistor along with component testing and verifying osc drive. wave forms.

When all that was normal, and I could get a beefier arc off the flyback lead to the rect than the HV connector I decided to re-check the new rect tube I installed last week...It was dead. I grabbed a weak rect. in the bag of original parts changed since I've owned the set and got full 25KV.

It was rather unexpected that a NOS part would test fine and rapidly die like that...Glad it is working again.
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  #24  
Old 03-09-2017, 07:39 AM
DaveWM DaveWM is offline
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I would not every use a tube tester on:
Damper/horz out/HV rec/shunt or regulator tube.

If you are having any HV issues it best to try subbing known working tubes in those areas. I don't think most tube testers can simulate the working environment of a tube, esp those.

I pretty much only rely on the shorts test before installing any new tube just to make sure it does not damage the set being worked on.
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  #25  
Old 03-09-2017, 08:31 AM
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Quote:
Originally Posted by DaveWM View Post
I would not every use a tube tester on:
Damper/horz out/HV rec/shunt or regulator tube.

If you are having any HV issues it best to try subbing known working tubes in those areas. I don't think most tube testers can simulate the working environment of a tube, esp those.

I pretty much only rely on the shorts test before installing any new tube just to make sure it does not damage the set being worked on.
I don't have another working set that uses the same HV rect or HOT so it is guess and test all the way with this TV....I was not relying on the tester for accuracy (though it was accurate*), but more of a confirmation the heater was not open and that it had potentially usable emission.

*That first replacement lasted ~3 hours putting out around 15KV before it died. The tester showed it as usable when it sort of worked and dead after it died....Hard to accurately test a tube for future life.

I'm used to NOS tubes being DOA, or healthy, but I'm not used to them acting healthy and dying rapidly when put into service.

I've got a issue with the color dropping out that I want to fix so I'm going to put some hours on it before I button it up...There could be some secondary issue killing HV rects.
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