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Old 03-05-2017, 09:23 AM
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Username1 Username1 is offline
Not sure how I got here.
Join Date: Dec 2009
Location: Orange County NY
Posts: 3,470
To be more clear: Take the cap off the 6BK4, then run the set.
This will take the shunt regulator out of the circuit.
By definition, the shunt regulator puts an additional load
on a power supply of limited current availability. It relies on
additional loading to provide voltage regulation.

Think of the HV supply as providing enough voltage and current
to run the picture tube. When the picture gets dark, beam current
would go down, reducing load on the HV supply. Voltage would
naturally go up. The 6BK4 should then conduct more, and load the
HV supply source, and bring down the voltage level.

Removing the HV lead, or plug at the end of the tube takes out the
main current user of the HV supply, HV should go up as it has a very
limited load at this time.

Normally, the set should supply 20 - 25KV to your set with a mid brightness
picture on the screen. You have to determine if the supply has a problem
or if there is a problem with the tube, or the reg.

It is fairly easy to disable the regulator. Then move on from there.

Your tv sure looks like it's producing a nice bright picture.

Yes you can call me "Squirrel boy"

Last edited by Username1; 03-05-2017 at 09:28 AM.
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Old 03-05-2017, 01:53 PM
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miniman82 miniman82 is offline
First Light: 1952-2011
Join Date: Jun 2009
Location: Great Mills, MD
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Originally Posted by VA561 View Post
Nick don't you miss it here in Norfolk? You could drop by here and perform surgery on the Zenith!
I tried to stay Larry, but they wouldn't let me! lol

Check the value of the resistors around the 6BK4 grid, I'm sure you'll find that one of them has drifted out of spec. Could also be the HV pot itself, use your DMM. Once you've replaced the bad parts, you should be able to set HV correctly with the pot.
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Old 03-05-2017, 02:08 PM
dieseljeep dieseljeep is offline
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Originally Posted by VA561 View Post
Just ordered n.o.s. 6BK4A-B and 3AT2 tubes. Is it ok to use a 6BK4A-B in place of the 6BK4?
Did you remove the HV rect tube socket and check the resistor in there?
Is it jumpered out, like it was recommended in another thread.
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Old 03-05-2017, 04:44 PM
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VA561 VA561 is offline
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Location: norfolk,virginia
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Going to tackle it next sat. Excellent advice from everyone. Much appreciated. I want to keep this set for a long time so I want to get it fixed.
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Old 03-06-2017, 09:28 AM
zeno zeno is offline
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Location: New Hampshire
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OK this was missed by all. If you turn the brite down on any
set the pix should go black or nearly so. Fix this first as it causes
an abnormal load on the HV. Start with a by the book set-up especially
the G-2's & bright limit. Could be just someone set them too
high to get a brighter pix. If not adjustments move to the
vid amp & blanking tubes. I remember NO scenario where the
HV will cause too much brite........
Normally I would start at the sweep then move on BUT the video
is so far off it could be the root of the problem.

73 Zeno

Originally Posted by andy View Post
Does the HV adjustment have any effect? There are two general causes of low HV. Either the flyback isn't outputting enough voltage (a bad HV rectifier could also cause this), or it's being loaded down by the regulator.

The HV adjustment has little to no effect. A strange thing, I can't get the screen to go black. The picture I posted of a blank screen was with the brightness turned all the way down.
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Old 03-06-2017, 09:25 PM
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VA561 VA561 is offline
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Zeno You nailed it! I had previously mentioned that I couldn't get a dark screen. Not even close and the best I could get was 16Kv. As per your suggestion, After turning the brightness knob down as far as it would go, I adjusted the three G2 controls and got a dark screen and most importantly........25Kv! I then brought up the G2 knobs up slightly to where I thought I had a decent picture. I guess the the fact that I couldn't get a dark screen caused you to consider the G2 settings. Thank you so much. I now have a full screen and a pretty good picture. After a convergence is done, that should do it.
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