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 Post subject: Re: Admiral 20X1 Excessive Width
PostPosted: Aug Fri 27, 2021 12:13 am 
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bandersen wrote:
I noticed an old sand coated power resistor above the VOT. These are often bad. Be sure to double check or replace it.


Oh, that shot was from an old picture back when I first got the set. That brittle little label on the transformer fell off shortly after that, so it's not there in later pics I have. Yes, that junky sand resistor and all other old parts in that pic are all gone now.


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 Post subject: Re: Admiral 20X1 Excessive Width
PostPosted: Aug Fri 27, 2021 12:43 am 
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I generally glue labels back on if they come off in a limited number of pieces.

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 Post subject: Re: Admiral 20X1 Excessive Width
PostPosted: Aug Fri 27, 2021 1:02 am 
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Tom Schulz wrote:
I generally glue labels back on if they come off in a limited number of pieces.

Oh yes, the label is in safe keeping. I'll take care of putting it back once all the chassis poking around is done! :D


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 Post subject: Re: Admiral 20X1 Excessive Width
PostPosted: Aug Fri 27, 2021 3:03 am 
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Tom Albrecht wrote:
On some models, the horizontal width is simply too large no matter how you adjust it. The manufacturer wanted to make sure the customer would never see a black bar on the left or right, regardless of line voltage, etc.

An easy method to reduce width, while keeping the HV unchanged (better for brightness, focus) is to wrap a little aluminum foil around the neck of the CRT where the yoke sits. Experiment a bit to figure out how much foil to add and you can fine tune it pretty well.

That was a method Zenith used for width adjustment in some of their sets.
However it was a sheet of brass that encircled the neck, you would adjust width by sliding the cylinder of brass sheet in or out of the yoke. It worked using eddy currents induced in the brass which neutralized some of the magnetic field. It mainly effected the width because of the higher horizontal frequency.
The brass had a clip that held it in place and also was connected to a grounded wire to prevent the brass from building up a charge.

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 Post subject: Re: Admiral 20X1 Excessive Width
PostPosted: Aug Fri 27, 2021 4:48 am 
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I wonder if the foil should be sprayed with some paint to minimize any chance of shorting to the yoke windings.

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 Post subject: Re: Admiral 20X1 Excessive Width
PostPosted: Aug Fri 27, 2021 5:38 am 
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Tom,

In the few cases where I’ve used this as a permanent fix, I wrapped the aluminum foil with electrical tape. Obviously you can’t get too thick or the yoke won’t fit properly, but a single layer of tape is OK and provides some short circuit peace of mind.

I find this approach is needed for Philco Safaris, which have bonkers excessive width, probably because it shrinks as the battery runs down. I’ve also done it on a few normal 1940s sets like this one.

FrankieKat,

In the first post, you mention that “a full rotation” of the width and linearity controls had no effect. These are slug tuned coils, and the full adjustment range would be 10-20 turns, with a single turn having almost no effect. Can you clarify what you’re seeing if you run the slug as far out of the width coil as possible (which would be the setting for minimum width)?

If you did indeed crank it 10-20 turns and there was no effect, have you confirmed that both halves of the tapped winding on the flyback for the yoke have continuity? If the wrong half is open, you might get excessive width and no effect for the width coil. You’ll have to disconnect one side of the width coil to check.

I realize the drive seems to be too high, but these are additional things to confirm.

One thing to check for excessive drive: Is the 8200 ohm resistor shunting part of the horizontal oscillator coil good? If it has gone high in value, you might get excessive drive. I realize you said you checked every resistor, but sometimes people skip measurements like this one which require disconnecting one side of the resistor to measure.

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 Post subject: Re: Admiral 20X1 Excessive Width
PostPosted: Aug Fri 27, 2021 4:42 pm 
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Tom Albrecht wrote:
FrankieKat,

In the first post, you mention that “a full rotation” of the width and linearity controls had no effect. These are slug tuned coils, and the full adjustment range would be 10-20 turns, with a single turn having almost no effect. Can you clarify what you’re seeing if you run the slug as far out of the width coil as possible (which would be the setting for minimum width)?

If you did indeed crank it 10-20 turns and there was no effect, have you confirmed that both halves of the tapped winding on the flyback for the yoke have continuity? If the wrong half is open, you might get excessive width and no effect for the width coil. You’ll have to disconnect one side of the width coil to check.

Yes, I have cranked the horiz width and linearity slugs through their entire rotation - some 20 odd turns, and no effect at all from either. I did disconnect one side and tested both the flyback winding and the control coil and both have continuity - the coil being very low resistance, something like 0.2 ohm. Also disconnected the linearity coil and it tested on spec at around 35 ohm. I visually checked to make sure the core was still in the coil and moving along with the screw, and it is.

Yesterday I went for broke and turned all of the horizontal slugs and trimmers (width, linearity, oscillator, lock-in, drive, lock range) all the way fully out to do the full horizontal calibration procedure. The issue is that the horizonal sync/lock is so strong on this set that it's almost difficult to get it to fall out of sync as described, requiring a fairly high number of rotations on the oscillator to get it to go out of sync. After that, rotating the front horizontal hold control from one side to the other restores the lock - at which point it won't go out of sync no matter the position of the hold control. The "lock-in range" capacitor/trimmer (not to be confused with the "lock" slug) doesn't seem to have a huge effect on the calibration but perhaps that's only because it takes so many turns of the the oscillator trimmer to even get it out of sync. Adjusting the horizontal lock slug is very responsive and I'm able to very easily dial in that waveform with the equal peaks... just that I'm seeing 95V PP instead of the 55V PP that Rider shows.

As for the front horizontal hold control, once the horizontal oscillator is calibrated rotating it either direction fully will not lose horizontal sync. It sort of has the effect of changing the center of the picture, moving it left and right a little bit... but never losing sync.

Here is a video of that: https://youtu.be/2wr-HT9Y_Gw

Tom Albrecht wrote:
I realize the drive seems to be too high, but these are additional things to confirm.

Makes total sense. I've just been using the PP voltages of the oscillator waveform (where you adjust for equal peaks) and the grid of the output tube as benchmarks for any changes. What led me there was Beitman's "Television Serving Course", page 183 suggests for excessive width:

  1. Maladjusted or open width control - width coil is fine
  2. Open flyback tapped winding - flyback is fine
  3. Low anode voltage - I have 9.25KV and great brightness/contrast
  4. Check horizontal drive waveform - waveform is perfect, voltage is too high

Thanks anyway Morris!

Tom Albrecht wrote:
One thing to check for excessive drive: Is the 8200 ohm resistor shunting part of the horizontal oscillator coil good? If it has gone high in value, you might get excessive drive. I realize you said you checked every resistor, but sometimes people skip measurements like this one which require disconnecting one side of the resistor to measure.

Yes, have checked that too, and measures ~8.8k, (7% off spec), so left it alone. Since it's paralleled with that coil (~35ohm) my original thinking was that the 7% won't make a big difference (the original part was 10%/silver anyway). I did just now try tacking in a perfect 8.2k, but didn't change anything. For what it's worth, the "lock" slug on that coil does do what it is supposed to in terms of affecting the lock in the front hold control.

Also, I did get two more 6SN7 tubes yesterday, and tried them in both places and sadly, no difference. So having tried 6 tubes, I think the sync clipper and horiz oscillator tubes can be safely eliminated as the problem. I'm expecting a different damper (6W4) tube any day now, as that's the only tube I haven't swapped out.

Try as I might, the only thing that affects the width is the drive control, which in order to get where it is now is fully closed down. It seems like if it were able to keep going it would get everything to where it needs to be. If I open it up, voltage goes even higher and width increases. Re-tested the resistors in that circuit and the 470K resistor across the drive trimmer is a brand new 1% metal film that tests as 469K on my DVM, and the 47ohm to grid tests as 47.3ohm. The 470pF coupling cap is the original, but I've pulled it out, tested it and subbed out a new 470pF and no noticeable change. The rest of the caps are all brand new film caps, either Panasonic or Orange Drops.

Several of the original wax caps that were in there had taken some obvious heat as the wax was quite melted and the the 8.2K resistor to the output tube screen looks a little charred. You can also see that where that .2 cap has melted the nearby yellow wire, which is a B+ line! Not surprisingly every single one of those paper caps tested completely bad. Attaching a picture of original as-found condition of that area for reference.

It's been suggested to try a higher value resistor to the grid of the output, and perhaps I could start to experiment with different values in the B+ circuit. It's been said too that it shouldn't be necessary to do any circuit bending to make the TV work as it should have originally, though at this point I'm up for anything that might clue this in. Literally the only thing that's out of spec from original is the primary on that VOT, but by all accounts that sounds like it's not relevant.

Thanks so much for all of the thoughts and suggestions. Anything else that I could try or test I'd be happy to and/or take photos, video, whatever!

FK


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File comment: Original condition of horizontal
orig_horiz_caps_2.jpg
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 Post subject: Re: Admiral 20X1 Excessive Width
PostPosted: Aug Fri 27, 2021 5:39 pm 
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Sounds like you are at the point where modification will be the only route to success. I personally think that that the foil wrap is the least disruptive (because it keeps your HV nice and high), but increasing the screen dropping resistor (which will also drop the HV), or adding a mica cap in parallel with the horizontal drive trimmer are also good options. If you go the last route, be prepared to mess a bit with the other components in the network of components feeding the HO grid, as these things usually affect the horizontal linearity.

I'm sure you've covered this already, but is the yoke fully slid forward on the neck of the tube? If it's not, width will be increased.

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 Post subject: Re: Admiral 20X1 Excessive Width
PostPosted: Aug Fri 27, 2021 6:02 pm 
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Tom Albrecht wrote:
I'm sure you've covered this already, but is the yoke fully slid forward on the neck of the tube? If it's not, width will be increased.

Tom, it's a very fair question. I haven't been inclined to touch the physicals too much yet until seeing about getting a handle on the electrical stuff, so I haven't thoroughly examined that.

The neck of this CRT is a bit tightly arranged with the focus coil and double ion trap magnet, and I don't see a lot of degrees of freedom to move things around much (other than the magnet). From the second picture though it looks to me like the yoke is pretty close to the CRT, though yoke and focus coil seem to be integrated into the CRT mount near as I can tell so I'm not sure if it's even really moveable, unless I'm missing something!

The long and short of it is, the TV is very watchable -- other than width and controls, it works great. I suppose my only concern about just leaving it as-is might be long term wear or damage on components (especially CRT) due to the over voltages and drive. Do you think that's a concern?

FK


Attachments:
File comment: top view
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crt_top_1.jpg [ 537.75 KiB | Viewed 570 times ]
File comment: yoke
crt_top_2.jpg
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File comment: Side view
crt_side_1.jpg
crt_side_1.jpg [ 552.21 KiB | Viewed 570 times ]
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 Post subject: Re: Admiral 20X1 Excessive Width
PostPosted: Aug Fri 27, 2021 6:36 pm 
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Tom Albrecht wrote:
Sounds like you are at the point where modification will be the only route to success. I personally think that that the foil wrap is the least disruptive (because it keeps your HV nice and high), but increasing the screen dropping resistor (which will also drop the HV), or adding a mica cap in parallel with the horizontal drive trimmer are also good options. If you go the last route, be prepared to mess a bit with the other components in the network of components feeding the HO grid, as these things usually affect the horizontal linearity.

Adding in some small mica caps does seem bring down the voltage and width a small amount (so at least something is working as expected). 50pF drops the drive voltage about 5V, though it does make vertical a bit more touchy. Still no perceivable response on the width and linearity controls though... so odd.


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 Post subject: Re: Admiral 20X1 Excessive Width
PostPosted: Aug Fri 27, 2021 6:49 pm 
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Am I correct in assuming that you just received this TV set? In other words, you can not say that it was working fine and then failed? If this is the case, there could be some problem induced by a previous person working on the set. There could be a wiring error or part value error. If the history of the set is unknown, all bets are off and the circuit has to be checked to see that it is wired correctly. Kind of like buying a non-working Heathkit. I know that this is a long shot, but I just can not believe that it left the factory the strange way it is acting.


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 Post subject: Re: Admiral 20X1 Excessive Width
PostPosted: Aug Fri 27, 2021 6:54 pm 
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As I understand it, when you reduce the drive you increase the amount of power consumed in the horizontal output tube and circuits. Increased drive will turn on the horizontal output tube harder when is is turned on but will keep it turned off longer when it is turned off. The horizontal output is turned on long enough to start the trace going across the screen. Then it turns off and the trace continues due to the horizontal output transformer ringing which causes current to flow through the damper.

So decreasing the drive is harder on the horizontal output tube and flyback.

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 Post subject: Re: Admiral 20X1 Excessive Width
PostPosted: Aug Fri 27, 2021 7:29 pm 
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J. Hill wrote:
Am I correct in assuming that you just received this TV set? In other words, you can not say that it was working fine and then failed? If this is the case, there could be some problem induced by a previous person working on the set. There could be a wiring error or part value error. If the history of the set is unknown, all bets are off and the circuit has to be checked to see that it is wired correctly. Kind of like buying a non-working Heathkit. I know that this is a long shot, but I just can not believe that it left the factory the strange way it is acting.

Correct, it was purchased with no known history. Just that based on my own assessment of it - dust, era of replacement components, condition of solder joints, the TV had not been touched in a long long time. Other than the VOT, CRT, some tubes, and a few paper/wax caps that were replaced by ancient paper/plastic caps, it was almost entirely original.

I have actually fully traced out all of the wiring and component values twice (from the vertical on at least), marking up two separate copies of the schematic with highlighters and there are no deviations or errors anywhere (would be great if there was!)... it perfectly matches the Run 12 revision in the service info. Yet no, I cannot prove absolutely that it didn't have excessive width before it was retired.

FK


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 Post subject: Re: Admiral 20X1 Excessive Width
PostPosted: Aug Fri 27, 2021 7:47 pm 
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It may be difficult to see the effect of the width and linearity controls unless you put a cross hatch test pattern on the screen. This is especially true of the linearity. Width you can monitor, provided you can see the edge of the raster (even if wrapped around the side of the tube). Then you have a sensitive visual reference of what's happening. But not sure you can see the edge from what you report. If both the width and linearity do absolutely nothing, even with a cross hatch on the screen, that is indeed fascinating. [edit: I see you show a cross hatch in your first post, so I assume you're saying you can't see any change in the crosshatch pattern when turning width and linearity all the way through their entire range.]

To knock the horizontal drive down to the spec value, you may need to add more like a few hundred pF in parallel with the trimmer.

From your pictures, it looks like the yoke position is correct. The way to check is to loosen the screws at the bottom of the bracket that's holding up the yoke. You can see the slots in your picture. If you loosen those you can slide it all the way forward. But it does look to me like it's already all the way forward and pushed against the bell of the CRT.

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 Post subject: Re: Admiral 20X1 Excessive Width
PostPosted: Aug Fri 27, 2021 8:32 pm 
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Tom Albrecht wrote:
It may be difficult to see the effect of the width and linearity controls unless you put a cross hatch test pattern on the screen. This is especially true of the linearity. Width you can monitor, provided you can see the edge of the raster (even if wrapped around the side of the tube). Then you have a sensitive visual reference of what's happening. But not sure you can see the edge from what you report. If both the width and linearity do absolutely nothing, even with a cross hatch on the screen, that is indeed fascinating. [edit: I see you show a cross hatch in your first post, so I assume you're saying you can't see any change in the crosshatch pattern when turning width and linearity all the way through their entire range.]

To knock the horizontal drive down to the spec value, you may need to add more like a few hundred pF in parallel with the trimmer.

I do have a cross-hatch generator, though I've just been using the EPG window display from the OTA box which should normally take up about 75% of the screen, which gives a fairly good reference for where the ends of the windows stop. You can actually see this better in the little video I posted: https://youtu.be/2wr-HT9Y_Gw .

As you predicted, adding about 280pF to the drive trimmer brought the voltage down to 35V (right where Rider says it should be) and that brought the picture about into the perfect width. At that point, I *think* that the width trimmer is making a very tiny change, we're talking less than 1/8" slug fully in vs fully out. And, also as you said, it took a hit on my HV. Went from 9.3KV to 7.5KV, so that's no good. Not sure what, but I guess this proves something... ?


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 Post subject: Re: Admiral 20X1 Excessive Width
PostPosted: Aug Fri 27, 2021 8:45 pm 
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Yeah, that sounds about right. 1/8" - 1/4" is all the width control will do.


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 Post subject: Re: Admiral 20X1 Excessive Width
PostPosted: Aug Fri 27, 2021 9:05 pm 
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bandersen wrote:
Yeah, that sounds about right. 1/8" - 1/4" is all the width control will do.

And with the width blown out, given how slow it is to get the width control from one extreme to the other, it makes sense that a change would be effectively imperceptible. At least this also means that the width and linearity circuit are in fact working. Progress!


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 Post subject: Re: Admiral 20X1 Excessive Width
PostPosted: Aug Fri 27, 2021 10:39 pm 
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I would normally expect 1/2 - 1 inch from a width control on a 10 inch set. I also have this model of set, so I should check it next time I get a chance to do so.

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 Post subject: Re: Admiral 20X1 Excessive Width
PostPosted: Aug Fri 27, 2021 10:57 pm 
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Tom Albrecht wrote:
I would normally expect 1/2 - 1 inch from a width control on a 10 inch set. I also have this model of set, so I should check it next time I get a chance to do so.

Interesting! If and when you do, I'd be curious about the PP AC voltage readings on the grid of the output tube and also terminal C on the horizontal osc/lock transformer!

Also - just got in a new 6W4 damper and, probably to no surprise, it made no difference. At least one more thing I can check off the list!

FK


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 Post subject: Re: Admiral 20X1 Excessive Width
PostPosted: Aug Sat 28, 2021 2:36 am 
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What would you think about going back to square one and tracing down that strange waveform that you showed us early on. That can not be right and I would bet it is part of the problem.


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