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  #1  
Old 01-03-2018, 11:36 AM
madlabs madlabs is offline
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Proper initial adjustment of a B&W

Hi All,

Thanks to the help on this site, I got my Predicta Holiday up and running last year. It works OK but there are multiple small issues still to be resolved. I am going to bring the set back to the bench this year, now that the Holidays are gone it's time to work on the Holiday! BTW, the kids and grandkids were wowed by it! One of the three year olds sat with me and watched two episodes of Honey West and was totally absorbed.

However, before I get to trying to track down the issues, I want to learn how to do a proper initial adjustment. I never got the linearity very good and I didn't even know that the yolk needs to be adjusted, other than to get the picture straight, so I just pushed it all the way up the neck.

I never came across a good tutorial on the process and procedures for doing an initial adjustment. What adjustment does one do first, second, etc. Since they all interact I'm sure that there is some "adjust A and B, then go back and tweak A" kind of things.

So does anybody have a resource for the proper adjustment of B&W sets?

As always, thanks for the help!
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  #2  
Old 01-03-2018, 12:48 PM
Electronic M's Avatar
Electronic M Electronic M is offline
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Sam's usually has a proceedure for the horizontal. The vertical is not so much step by step as it is mess with height lin and centering simultaneously for best results....One thing you could try is pulling the vert sweep tube with brightnessat min so the line don't burn the screen vertically center the line then plug the tube back in and try to get height and lin dead on.

If you can't get vert linearity right with the screen filled/overfilled something is wrong with the circuits.

Monochrome sets were designed to have signifficant overscan (underscan = warranty complaint=lost profit) to compensate for fluctuations in house hold voltage and unregulated B+ supplies. So don't bother trying to get overscan down....Fighting the design limits is not a good practice.
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Old 01-03-2018, 01:00 PM
zeno zeno is offline
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For yoke straiten & push up til you get no neck shadow. Usually all
the way is fine.
For size & lin put up cross hatch or a big circle & adjust. You have to
go back & forth. Overscan the pix a little too. If you cant adjust
it right check the high ohm resistors near the controls & the electrolytic
in the cathode of the vert out.
AGC with strong signal turn up til it starts tearing, buzzing etc then turn
it back til it just stops.
If it has hoz size or lin do same as in vert.
Horz osc sometimes has a procedure.
Anything else should be handled as needed one part at a time.
DO NOT turn any coils !

73 Zeno
LFOD !
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  #4  
Old 01-04-2018, 10:00 AM
madlabs madlabs is offline
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Quote:
Originally Posted by Electronic M View Post
The vertical is not so much step by step as it is mess with height lin and centering simultaneously for best results....
And IIRC centering is with the magnets in the yoke?

Quote:
Originally Posted by Electronic M View Post
One thing you could try is pulling the vert sweep tube with brightnessat min so the line don't burn the screen vertically center the line then plug the tube back in and try to get height and lin dead on.
OK, so minimum brightness and then center the line on the screen. Got it.

Quote:
Originally Posted by Electronic M View Post
If you can't get vert linearity right with the screen filled/overfilled something is wrong with the circuits.
There could well be. That's why I want to try to learn how to do a proper adjustment.

Quote:
Originally Posted by Electronic M View Post
Monochrome sets were designed to have signifficant overscan (underscan = warranty complaint=lost profit) to compensate for fluctuations in house hold voltage and unregulated B+ supplies. So don't bother trying to get overscan down....Fighting the design limits is not a good practice.
How do I determine proper overscan?

Quote:
Originally Posted by zeno
For yoke straiten & push up til you get no neck shadow. Usually all the way is fine
What is neck shadow? And does the yoke position affect the focus at all? Or anything else?

Quote:
Originally Posted by zeno
AGC with strong signal turn up til it starts tearing, buzzing etc then turn it back til it just stops.
So, crank up the signal from my BT modulator, then back it off? What is tearing?

Thanks folks!
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  #5  
Old 01-04-2018, 11:23 AM
dieseljeep dieseljeep is offline
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Quote:
Originally Posted by Electronic M View Post
Sam's usually has a proceedure for the horizontal. The vertical is not so much step by step as it is mess with height lin and centering simultaneously for best results....One thing you could try is pulling the vert sweep tube with brightnessat min so the line don't burn the screen vertically center the line then plug the tube back in and try to get height and lin dead on.

If you can't get vert linearity right with the screen filled/overfilled something is wrong with the circuits.

Monochrome sets were designed to have signifficant overscan (underscan = warranty complaint=lost profit) to compensate for fluctuations in house hold voltage and unregulated B+ supplies. So don't bother trying to get overscan down....Fighting the design limits is not a good practice.
BTW, how did your Predicta turn out. The one you bought last summer.
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Old 01-04-2018, 01:20 PM
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Quote:
Originally Posted by dieseljeep View Post
BTW, how did your Predicta turn out. The one you bought last summer.
Standard recap & rebuild of the headshell harnesses (some dope hacked them up real bad) got me this.

DSCN2759 by Tom Carlson, on Flickr

I still need to do something about the couplates since vert sync is very weak, but it is doing good enough. When I can find a decent place to display/use it I'll revisit the couplates.
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Old 01-04-2018, 02:01 PM
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Quote:
Originally Posted by madlabs View Post
And IIRC centering is with the magnets in the yoke?

How do I determine proper overscan?

What is neck shadow? And does the yoke position affect the focus at all? Or anything else?

So, crank up the signal from my BT modulator, then back it off? What is tearing?

Thanks folks!
Centering magnets are on the back of the yoke. They are the rings that the neck passes through they have two ears to grab and rotate. The centering rings affect both horizontal and vertical centering simultaneously.

There is no hard and fast standard for overscan. If total horizontal overscan is under 1/3 of total scan width and the screen is filled then it is within normal range....Overscan varies heavily with utility voltage, health of the tubes, etc....That is why it is best to not to aim for any specific spot on the dart board but just be sure to hit the board somewhere. Horizontal overscan is usually the hardest to control, so whatever the horizontal is, best live with it and adjust the vertical to match....so round things (like clocks) look round and not oval.
Some of my tube color sets that I do serious watching on I actually adjust the underscan by using a variac to change the AC power input voltage.

Neck shadow is more commonly seen in early post-war sets....Basically, it manifests its self as curved unchanging dark patch near the edge of the screen.

AGC is not a knob on your modulator, but rather it is a knob on most TVs...IIRC most predictas were too cheap to have an actual AGC pot and instead had the Local-Distant range switch normally reserved for loss leader portable sets....Which brings up another point:

These predictas have very cheap crude circuit designs, they are not tube broadcast monitors, Dumonts or even Zeniths....Sweep is not going to be as precise or adjustable as even the middle of the road brands of the day letalone the solid state CRT sets we often subconsciously use as yardsticks to compare all CRT sets against. Perfection is a waste to pursue as it will constantly drift away from it even if achieved.

As long as round objects are round, a cross hatch grid is fairly reasonably even spaced in both axes, the center of the image is within 1.5" of the CRT center, and not more than 1/3 overscan or any underscan then your set would probably be in the top 60% of performers if you went back in time and compared it to other predictas when they were new...And you will not notice problems watching natural sceenes and period material....Some modern material letterboxing, sports and news graphics, DVD menus, etc mimic test patterns and show off the design limitations of such TVs.....It is sort of like feeding a HiFi test/demonstration recording into a 30's table radio or a 60's transistor radio; The limits of the circuits are made (somewhat painfully) obvious.
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  #8  
Old 01-04-2018, 02:31 PM
zeno zeno is offline
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Tom C. has very good points about perfection. TV's were built aimed at
a price point. Some were slapped together almost to the point
of unservicability, low parts count & barely operating under the best
conditions. Others built with a very high quality without leaving things out.
Most fell in the middle.
So the idea is to return the TV to a decent pix & sound that is stable
& watchable. Some by nature will be better than others.
I never worked on a Predica, the boss did one once so I saw the guts.
It looker real unpleasant !! Remember Predictas are in demand due to
the styling NOT the electronics.

73 Zeno
LFOD !
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  #9  
Old 01-05-2018, 02:22 PM
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bandersen bandersen is offline
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Quote:
Originally Posted by Electronic M View Post
Centering magnets are on the back of the yoke. They are the rings that the neck passes through they have two ears to grab and rotate. The centering rings affect both horizontal and vertical centering simultaneously.
Not in a Predicta. Phil put up a scan on his website showing the locations. There are two magnets you can rotate for the centering.

The "T" bar on the left can be push forward and pulled back to adjust the horizontal linearity. Twist it a little for distortions in the corners. It's crude for sure so don't expect perfection.



Here's the whole article: https://antiqueradio.org/philc12.htm
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Old 01-05-2018, 02:56 PM
Electronic M's Avatar
Electronic M Electronic M is offline
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Quote:
Originally Posted by bandersen View Post
Not in a Predicta. Phil put up a scan on his website showing the locations. There are two magnets you can rotate for the centering.

The "T" bar on the left can be push forward and pulled back to adjust the horizontal linearity. Twist it a little for distortions in the corners. It's crude for sure so don't expect perfection.



Here's the whole article: https://antiqueradio.org/philc12.htm
Pretty sure the yoke in my 17" Predicta did have rings, but with how hacked up the yoke wiring was it may not have even been the original yoke...
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  #11  
Old 01-05-2018, 05:41 PM
madlabs madlabs is offline
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I don't think I have too high expectations. I get that this is an older and not that great set in the first place. I can't seem to find the picture I took of a test pattern. Does anybody have a shot of their Predicta displaying a test pattern?

I suspect I still have issues in the set. By the time I got it working as well as it does now I had had enough and since it played OK I decided to use it for a while and enjoy it. Now it has been long enough that I have the desire to go back and see how much I can improve it.

Thanks!
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