Hi all. Have the 6T65 16GP4 RCA working OK (more troubleshooting advice needed for a different issue than this). The picture is slightly bent pinched in a bow shape top and bottom and side to side. Obviously something to do with the yoke. Any ideas on what might be going on?

https://imagizer.imageshack.com/v2/1024x768q70/924/CP7Q3m.jpg

Edges appeared straight back in this photo, what has changed? Are you sure the yoke is all the way up to the CRT?


https://imagizer.imageshack.com/v2/1024x768q70/923/2u8kpd.jpg

I suspect the sides are straight in the first picture and the curved mask is tricking the eye. For stuff like this a crosshatch test pattern is a good idea as regular programming content and mask shape can obscure the actual nature of what you're looking at.

What's different is the yoke. Let me explain. The cockeyed picture is with my restored chassis from the original dark wood TV transplanted to the blonde cabinet and the yoke on the CRT original to the maple set. After an afternoon monkeying around with its original yoke to straighten out the picture without success, I took it off. The set screw wing nut that allows you to rotate the yoke was cross threaded and you couldn't tighten it down and, the yoke didn't look too good. OK I thought, just take the yoke off the dark cabinet set and put it in the maple set so now. the restored chassis is paired to the yoke it powered in the dark TV. The picture in the original TV didn't have this problem so it probably is a positional issue but I don't know how movement in and out along the neck could cause this.

If the yoke is too far back the beam can be obstructed by the aperture of the electron gun. Also the positioning of the Ion trap can have some influence, since it also bends the electron beam. The trap should be adjusted for maximum brightness with the yoke all the way forward against the CRT bell housing.

If the yoke is too far back the beam can be obstructed by the aperture of the electron gun. Also the positioning of the Ion trap can have some influence, since it also bends the electron beam. The trap should be adjusted for maximum brightness with the yoke all the way forward against the CRT bell housing.

Ok I’ll make sure that’s the case. Stand by

Also makes me think of a low voltage issue. Did anything in that part of the circuit change?

Also makes me think of a low voltage issue. Did anything in that part of the circuit change?

That could be too. In general there seems to be an under scan issue. Ordinarily one should be able to fill the mask plus a little more to keep from seeing the edges during line voltage fluctuations. Chris you may want to consider posting your picture over on the ARF forum. Things seem a little slow around here and their are some really sharp engineering types over there as well.

Under the principle of "fix the obvious first," the straight edged picture is with one yoke and the curved edge pic is with a different yoke, right?

I would suggest going back to the first yoke to verify that this change is due to the yoke and nothing else. If that's the case, it may be that the yoke that produces curved sides has either a different winding pattern and or metal/magnetic elements that produce the curve and is intended for a different CRT/receiver, on which it would produce straight edges. Or it may be missing some elements that would correct the curved edges.

Can you see any adjustable pieces on either yoke?

This yoke made a straight edged picture in the original tv in other words, if I had harvested the 16GP4 from the maple set and installed it in my original dark cabinet, as was the plan, it would e the exact same situation. When I got the maple tv with the strong CRT, it had its original yoke and chassis. I took my restored chassis from the original tv and put it in the maple tv but left in the yoke that was in the maple producing the small crooked but straight edged picture. I couldn’t get that yoke to produce a full screen picture so I pulled the yoke from the original tv. This chassis yoke combo produced a dim but straight edged picture in the old set with the weak CRT. I don’t know what could possibly be different other than I didn’t put the yoke in correctly when I did the swap

That could be too. In general there seems to be an under scan issue. Ordinarily one should be able to fill the mask plus a little more to keep from seeing the edges during line voltage fluctuations. Chris you may want to consider posting your picture over on the ARF forum. Things seem a little slow around here and their are some really sharp engineering types over there as well.

I’m going to play with the yoke that’s in it currently and make sure this is a real problem and not some error I made when installing the yoke. The only other thing is Tom mentioned this chassis and the yoke are a bit unique. But I can’t see why that would make a difference. The only things that are different is it’s a stronger CRT and I put in the yoke. This yoke/chassis combo was fine in the old set in terms of deflection…the picture was bad because the CRT is weak. Now that chassis and yoke is in a cabinet with a strong tube so this should work shouldn’t it? If I had swapped the CRTs instead we’d be in the same configuration but in a different cabinet so that’s why I need to make sure the yoke is in there correctly.

. Now that chassis and yoke is in a cabinet with a strong tube so this should work shouldn’t it? If I had swapped the CRTs instead we’d be in the same configuration but in a different cabinet so that’s why I need to make sure the yoke is in there correctly.

All assuming both KCS 47 chassis us the same direct drive yoke part number, which I don't know how they couldn't, but something is obviously different between the two. Any difference between the 2 focus magnets? If I'm not mistake the yoke has an octal plug that connects it to the chassis, so there's no way it can be mis-wired. :scratch2:

Correct the socket is on the side of the high voltage cage

If you can't get to the bottom of this, I'd suggest repairing the striped adjustment thumb screw treads on the yoke original to that chassis. Then you'll at least have a known baseline to move forward. Things can easily get wonky when you randomly start changing out parts.

Help me understand - this yoke produced a straight sided image with the same CRT type number or different? With the same focus coil and CRT accessories, or different?

Making a straight raster curve like that is not a minor difference, you should be able to find it.

I got it. The yoke in the maple TV from my restored TV giving me "the bends" is fine. The wing nut that holds it to the focus frame not only provides rotating the yoke when it's loosened but, the trapped nut on the yoke the wing "screw" threads into allows the yoke to travel forwards and backwards as well. The only way you can do this (because the yoke itself is in a housing and you can't get hands on it to push it closer to the CRT) is to loosen the nut and take a screwdriver and push the yoke forward and screw the wing nut tight while it's pushed. Then you need to check the yoke position on the bottom to be sure top and bottom are pushed forward equally. I think it's a bad design. If you need to rotate the yoke for an adjustment, you can't tell if the yoke has slipped back away from the CRT. You can't see it to check. Anyway, the picture fills the screen now with no bends. I'm eventually going to remove the entire housing and yoke to be sure everything is in the correct position. I only figured this out by working on the other yoke assembly that was originally in the strong CRT maple TV. On the bench it was easier to identify the potential problem. Thank you again Videokarmers!!!

Congratulations.
Is this the same bracket you're dealing with? Here it's missing the focus coil on the rear as it's jigged up on a KCS 40 chassis with the 5AP4 test crt, which needs no focus. This chassis is for a TC166 console which also has the 16GP4 crt.

https://live.staticflickr.com/65535/54857961926_467c3dfa14_z.jpg

Yes that's it. Can you see it's the captured nut on the yoke that allows it to be m0ved forwards and back but you can't make that adjustment by holding the wing screw. Only side to side.

Congratulations.
Is this the same bracket you're dealing with? Here it's missing the focus coil on the rear as it's jigged up on a KCS 40 chassis with the 5AP4 test crt, which needs no focus. This chassis is for a TC166 console which also has the 16GP4 crt.

https://live.staticflickr.com/65535/54857961926_467c3dfa14_z.jpg

Now that I can see how you have rigged this and I'm more familiar with the yoke/focus assembly, I might be able to pull the chassis and work on it for real on the bench. I have a 5AXP4. I see your ground clipped to the bracket. How did you get HV from the output socket on the HV cage to the test CRT? Is there anything more to removing the focus coil than removing the screws on the top (seen in your picture) and bottom? If I can work on it out of the cabinet, we can move on to the next issue...channel and sound not matching up. Been through this before and I hope there's an answer other than doing a full alignment!!!

I have an additional topic I'll post separately. The horizontal deflection circuit on these early TVs confuse the hell out of me. The KCS 47 has a horizontal hold, horizontal frequency, horizontal waveform, horizontal drive, horizontal lock, horizontal linearity and width adjustments. Just kill me now!

Yes the two rear screws with big brass washers remove the focus coil. Those washers are oversized so there's movement to center the fucus coil around the neck. The HV lead from the cage I have alligator clipped to another short HV lead with a normal anode button connector. Notice the large heat shrink that should be slid over that scary alligator interconnection while turned on.

I'm not sure if you realize those two elongated outer slots outside the yoke cage are the intended way to move the entire yoke assembly fore and aft along the CRT neck. I'm referring to the two slots I have the cage screwed onto my wood block supporting the test crt and yoke assembly. I'm using a spare yoke bracket and leave the sets hardware in the cabinet, so the 16GP4 stays mounted in the cabinet.

https://live.staticflickr.com/65535/54858905441_5302a3d41f_z.jpg

https://live.staticflickr.com/65535/54859162143_4f3636a096_z.jpg

By the way the ground lead clipped to the bracket is just for piece of mind there's no voltage from the yoke leaking to it. :D

Thanks Kevin...those 2 slots along the housing for mounting move the housing closer but if the yoke body is slid back within the housing, I still needed to slide the yoke forward. I can see in the anode setup photo, your yoke is in the forward position within the housing. My situation was the housing was pushed along the slots as far forward as the rubber cushions would allow but the yoke wasn't as far forward in the housing as it should have been.

Thanks Kevin...those 2 slots along the housing for mounting move the housing closer but if the yoke body is slid back within the housing, I still needed to slide the yoke forward. I can see in the anode setup photo, your yoke is in the forward position within the housing. My situation was the housing was pushed along the slots as far forward as the rubber cushions would allow but the yoke wasn't as far forward in the housing as it should have been.

Makes sense. Just remember when mounting yokes you can't really get them too close to the CRT, so everything should be maximized in that direction. Also allows for more clearance of the focus coil movement, as you don't what that bumping into the rear of the yoke.

Is there any issue with the yoke making contact with the CRT?

Is there any issue with the yoke making contact with the CRT?

Sure, if there's a grounded dag coating and the yokes winding insulation fails. But that's the reason for those rubber bumpers. But as you probably noticed the housing limits it from exiting too far out the front.

Point taken!

I wonder if there's anything proactive that one can do to prevent winding insulation failures in yokes, power transformers etc. If you took a transformer core and submerged it in a varnish or shellac filled container for a period of time, could the insulation be beefed up to extend the life of the component? All these things will fail one of these days.

I wonder if there's anything proactive that one can do to prevent winding insulation failures in yokes, power transformers etc. If you took a transformer core and submerged it in a varnish or shellac filled container for a period of time, could the insulation be beefed up to extend the life of the component? All these things will fail one of these days.

Don't know the answer in terms of a detailed procedure, but I do recall cases where the item being potted is put in a vacuum chamber to expell any air bubbles caught in the item - dunking may not be sufficient.

Don't know the answer in terms of a detailed procedure, but I do recall cases where the item being potted is put in a vacuum chamber to expell any air bubbles caught in the item - dunking not be sufficient.

Over on the ARF there's a couple Australian engineers that swear on cooking transformer windings in mineral spirits to dissolve any wax. And while it's still hot dunk in marine grade polyurethane varnish. The theory goes the hot mineral spirits draw the vanish inside and replace the solvent as it evaporates. There's a write up of the process.

Hi to all,
Hi @Kevin Kuehn,

the ARF thread on saving/restoring flyback transformers is here :
illustrated by many photos.

https://antiqueradios.com/forums/viewtopic.php?t=444436

See also the flyback restoration section (pages 2 to 4) in a Bush TV22 UK TV restoration article by ACORNVALVE of Australia.
38 page pdf, color photos :

https://worldphaco.com/uploads/BUSH_TV22.pdf

Best Regards
jhalphen
Paris/France

Over on the ARF there's a couple Australian engineers that swear on cooking transformer windings in mineral spirits to dissolve any wax. And while it's still hot dunk in marine grade polyurethane varnish. The theory goes the hot mineral spirits draw the vanish inside and replace the solvent as it evaporates. There's a write up of the process.
Last comment from me as I feel the "SEPARATE SUBJECT REQUIRED!" wrist slap is on its way!

I read several of them and they are fascinating. In addition, I'm a little apprehensive about the health and longevity of my TVs with a flyback winding exposed by cracking and/or melted wax. I have several Philco restorations that have that era of flyback and I have a designer, special edition Hallicrafters 7" that exhibits the heat related fading brightness symptom. I think I should probably get to them with some corona dope sooner rather than later.

I suppose the most efficient way to drag varnish into the windings is to match the base solvents as closely as possible.

Last comment from me as I feel the "SEPARATE SUBJECT REQUIRED!" wrist slap is on its way!

I read several of them and they are fascinating. In addition, I'm a little apprehensive about the health and longevity of my TVs with a flyback winding exposed by cracking and/or melted wax. I have several Philco restorations that have that era of flyback and I have a designer, special edition Hallicrafters 7" that exhibits the heat related fading brightness symptom. I think I should probably get to them with some corona dope sooner rather than later.

I suppose the most efficient way to drag varnish into the windings is to match the base solvents as closely as possible.

My advise is try not to go crazy obsessing over the longevity of any vintage electronics. Try as we may these things aren't going to last forever, and will require ongoing maintenance to keep them working in the midterm. But our lives are relatively short, so enjoy them while you can. This is my fatherly advise for the day. :D

Last comment from me as I feel the "SEPARATE SUBJECT REQUIRED!" wrist slap is on its way!

I read several of them and they are fascinating. In addition, I'm a little apprehensive about the health and longevity of my TVs with a flyback winding exposed by cracking and/or melted wax. I have several Philco restorations that have that era of flyback and I have a designer, special edition Hallicrafters 7" that exhibits the heat related fading brightness symptom. I think I should probably get to them with some corona dope sooner rather than later.

I suppose the most efficient way to drag varnish into the windings is to match the base solvents as closely as possible.

Nobody has had any luck with fixing the original HV osc transformers in 7" halicrafters. Easiest thing is to find a Motorola TS-4 or TS-18 chassis set (the most common electrostatic TV) with a dead CRT or cabinet beyond restoration and steal the HV transformer from it. Copy the Motorola HV osc circuit but use a 8BQ5 instead of a 25L6. Replace the 6C4 heater with a resistor. The Hallicrafters has a split heater string that converges at the 6X5s hot heater pin (it's other heater pin goes to ground). Ungrounf the 6X5s grounded heater pin and insert the 8BQ5 heater between that and ground. I did this modification on my Hallicrafters and it's been solid ever since.

My advise is try not to go crazy obsessing over the longevity of any vintage electronics. Try as we may these things aren't going to last forever, and will require ongoing maintenance to keep them working in the midterm. But our lives are relatively short, so enjoy them while you can. This is my fatherly advise for the day. :D

Now that’s funny 😄 Actually I still have my dad rattling around at 96 telling his 65 year old son the same thing!

Nobody has had any luck with fixing the original HV osc transformers in 7" halicrafters. Easiest thing is to find a Motorola TS-4 or TS-18 chassis set (the most common electrostatic TV) with a dead CRT or cabinet beyond restoration and steal the HV transformer from it. Copy the Motorola HV osc circuit but use a 8BQ5 instead of a 25L6. Replace the 6C4 heater with a resistor. The Hallicrafters has a split heater string that converges at the 6X5s hot heater pin (it's other heater pin goes to ground). Ungrounf the 6X5s grounded heater pin and insert the 8BQ5 heater between that and ground. I did this modification on my Hallicrafters and it's been solid ever since.

Thanks Tom. I’ll have to get that set out of storage and give it some CPR. I thought it was a not working for parts sale on eBay but someone before the flipper who sold it to me restored everything. All caps, all resistors…absolutely everything so I haven’t done too much to it except put it on a shelf

Did you fix the hourglass issue? It is not the yoke.

Did you fix the hourglass issue? It is not the yoke.

No my friend, it's not fixed. The temporary viewing Band-Aid is to increase the image zoom using a Zenith converter box so the letterbox borders are off screen but, you can still see the bends in any sort of straight horizontal or straight vertical images. I had the TV show "Concentration" on where there's a crosshatch letterbox game board and you can see it there.

Just a quick edit of this post. The bending was reduced when I pushed the yoke forward and the zoom made it watchable, so I was happy with it and that's why I sorta put it to rest but yes P'thode, the problem still exists although it's far less noticeable. It has always struck me that this is probably a voltage issue with the B+ being low...at least the B+ going to the yoke. To be honest, I've not checked the DC level on the TV but there's a NOS 5U4 in it so my confidence stemmed from that.

The barrelling is what is known as pincushion. It is exacerbated by the geometry of the tube eg wide deflection angle and flat screen. I don't that is the case here.
What I think your case is due to is magnetization of the steel CRT bell. The beam as it deflects to the edges of the raster image is likely being affected by the magnetism of the bell.
I suspect if you can degauss the CRT bell, the pincushion effect will disappear and the edges of the raster will be straight.

The barrelling is what is known as pincushion. It is exacerbated by the geometry of the tube eg wide deflection angle and flat screen. I don't that is the case here.
What I think your case is due to is magnetization of the steel CRT bell. The beam as it deflects to the edges of the raster image is likely being affected by the magnetism of the bell.
I suspect if you can degauss the CRT bell, the pincushion effect will disappear and the edges of the raster will be straight.

How could that be done? A degaussing hoop I have seen others use??

There are a thousand Chinese made degaussing wands for sale on eBay for <$20 but they are all 220V

Degaussing coil is the way to go. There's 2 that I can vouch for. One option is pick up a vintage service degaussing coil (about 14" diameter) off eBay or from a radio swapmeet. Another option is to find a junk 20" screen or bigger BPC and use it's coil to Make your own service coil. I've got a sticky in one of the sections on this topic. If you go with the latter don't leave it plugged in for more than 20 seconds...They overheat if left on.
You can do the degaussing with the TV on to see the effect if you like.

Thank you Tom

Degaussing coil is the way to go. There's 2 that I can vouch for. One option is pick up a vintage service degaussing coil (about 14" diameter) off eBay or from a radio swapmeet. Another option is to find a junk 20" screen or bigger BPC and use it's coil to Make your own service coil. I've got a sticky in one of the sections on this topic. If you go with the latter don't leave it plugged in for more than 20 seconds...They overheat if left on.
You can do the degaussing with the TV on to see the effect if you like.

I'm sorry, what do you mean by "I've got a sticky in one of the sections..."?

I will be waiting with bated breath to see if degaussing fixes this.

Magnetization of a 21AXP22 color CRT has noticeable effects on purity, but not such gross effects on geometry. On the other hand, the high voltage is lower here so magnetic effects could be stronger.

Has anyone seen such pincushion due to bell magnetization before?

Here is the effect again

https://imagizer.imageshack.com/v2/1280x1024q70/924/CP7Q3m.jpg

I will be waiting with bated breath to see if degaussing fixes this.

Magnetization of a 21AXP22 color CRT has noticeable effects on purity, but not such gross effects on geometry. On the other hand, the high voltage is lower here so magnetic effects could be stronger.

Has anyone seen such pincushion due to bell magnetization before?

I had on a 16AP4. It was only one corner though.

Rational thought suggests the only thing that causes pincushioning is a wide deflection angle on a flat screen or stray magnetism near the screen.

You could test by locating a not too strong magnet near to the rim of the CRT. However the bell is at at voltage so you would need to be extremely careful.

I thought about pincushion but have never heard of anyone have that problem on this old of set. Would you degauss from the front or the back side, or no matter?

I'm not going to get within 5" of this CRT so doing anything inside the cabinet while it's on is something I can't risk...not with my unsteadiness (from medication). If I am going to do any demagnetizing, my only options are outside while it's on or inside when it's off.

Degaussing coils are still relatively available due to the prevalence of old arcade units with standard CRTs.

I guess I could put the chassis and yoke back in the unit with the weak CRT and see if it produces a proper image. That would all but confirm Penthode's suspicions of a magnetized CRT bell.

I thought about pincushion but have never heard of anyone have that problem on this old of set. Would you degauss from the front or the back side, or no matter?

Monochrome tube does not have a shadow mask. In this case you want to run the degaussing coil all around the bell.

A thought: is it possible this set is intended to have some anti-pincushion magnets or pole pieces that are missing?

A thought: is it possible this set is intended to have some anti-pincushion magnets or pole pieces that are missing?

I don’t see any on either set. It does have permanent magnets in the focus ring but they are a ways away from the tube.

And there’s no mention of anything like that in the Rider’s service info which has an extensive setup section

A thought: is it possible this set is intended to have some anti-pincushion magnets or pole pieces that are missing?
The fixed anti pincushion magnets only appeared with the later wide deflection angle CRTs in the 1960s. I recall seeing them on later sets.

The 70 degree tubes like the 16GP4 generally did not suffer from pincushioning or raster distion unless there was a strong external magnetic field nearby.

My guess it is a magnetized cone are the corner distortions as the beam reaches a sweep extremity.

Monochrome tube does not have a shadow mask. In this case you want to run the degaussing coil all around the bell.

If that’s the case, maybe I should get the cheap wand style on eBay. I’d have to find a way to get 220V to it.

A thought: is it possible this set is intended to have some anti-pincushion magnets or pole pieces that are missing?

I haven't noticed any on the 2 or 3 sets I've had here with 16GP4's. If that was a thing wouldn't it be listed on the 16GP4 data? I have seen magnets on newer rectangular tube yoke assemblies.

I would think the best thing to do is to remove the tube from the set and go over the tube with a color TV degaussing coil.

I haven't noticed any on the 2 or 3 sets I've had here with 16GP4's. If that was a thing wouldn't it be listed on the 16GP4 data? I have seen magnets on newer rectangular tube yoke assemblies.

It wouldn't normally be a problem with a 16GP4. Unless in the past the tube was subjected to a strong magnetic field.

One thing that bothers me about this set Chris is working on is that the raster apparently won't fill the mask. I would definitely be verifying the power supply voltages.

For some perspective here's my Sentinel with a 19AP4 crt. You can definitely see some outward bowing, which seems quite normal for one of these big flat face tubes. Some of it is distortion from the face curvature. Never mind the guy peeking out from inside the TV.

https://live.staticflickr.com/65535/54873751778_50a4159cce_z.jpg

https://live.staticflickr.com/65535/54873537196_ffa835166e_z.jpg

https://live.staticflickr.com/65535/54873838800_f384803dbb_z.jpg

One thing that bothers me about this set Chris is working on is that the raster apparently won't fill the mask. I would definitely be verifying the power supply voltages.

Definitely going to do that Kevin. Like I said before I never checked it because the rectifier is new.

The picture on your Sentinel looks like the reciprocal of what I have on mine. Very interesting looking distortion.

It is opposite, but this is more normal of these vintage sets. The 19AP4 is set back behind the safety glass a significant distance. So there's some optical distortion from that. And the camera doesn't do it any justice. When watching a program it's not as obvious as these pictures indicate. I expect back in the day no one thought much of the shortcomings. There wasn't any alternative other than a movie theater. Technology advanced significantly over the next 10 years.

I'm sorry, what do you mean by "I've got a sticky in one of the sections..."?

A sticky is a topic that stays at the top of the forum section despite other newer topics happening. In this case it's a sticky in the radio TV tech forum section. https://videokarma.org/showthread.php?t=264048

Chris,

Tonight I fired up my RCA TC-166(KCS 40A) chassis with the 5AXP4 test crt and put a DVD test pattern on it. To my surprise it shows the same concave edges you're experiencing. I don't remember it being like this, but I probably never used a test pattern when working with it earlier. This weekend I'll attempt to slide this back in it's cabinet and see if the 16GP4 makes any improvement. Right now I'm not sure what to make of it.

https://live.staticflickr.com/65535/54876232080_f477f43e5d_z.jpg

Wow!

The slight bend is normal. It is due to the geometry of the CRT. The greater the deflection angle, the greater the bend.

The 15GP22 color CRT has a flat panel screen mounted internally within the tube. Because of this, the pincushion is very noticeable.

Wider deflection angle tube used pincushion correction. For monochrome sets, permanent magnets were used. For color, the introduction of the 25" rectangular CRT in 1965 required dynamic pincushion correction circuitry because permanent magnets would affect color purity.

I still contend the bell of the replacement 16GP4 has become slightly magnetized and removing the tube and carefully going over it with a degaussing coil will alleviate the problem.

Perhaps it was intentional to counteract the outward curve of the CRT face in metal cone CRTs?
https://live.staticflickr.com/65535/53940468869_ec25e2e196_c.jpg (https://flic.kr/p/2qbx18X)

So I should go over the metal bell correct…not do the withdraw circling from the screen

Considering the electron beam scans from a center point behind the crt face, it makes sense there will be distortion more so as it moves outward, predominantly in the horizontal scan. Back at this time RCA must not have considered it a serious enough problem to require correction. I'm not aware of any round screen monochrome set that implemented pincushion correction.

Perhaps it was intentional to counteract the outward curve of the CRT face in metal cone CRTs?
https://live.staticflickr.com/65535/53940468869_ec25e2e196_c.jpg (https://flic.kr/p/2qbx18X)

Problem for me is it can be seen when the image has straight lines in it. As you get towards the center it’s not noticeable but it is the last 2” or so of the vertical and horizontal limits of the tube

Is that image a zoomed image from the settings on your converter box Bob? Is that how you got it to fill the screen?

I'm feeding this set a standard 4:3 aspect ratio image. It's a Zenith porthole set in zoom mode. The set is designed to fill the entire screen in this mode by over scanning.

I’m going to try to demagnetize the metal crt bell. As good a place to start as any.

Yes the slight curvature to the faceplate help to reduce the pincushion effect
Only the much later monochrome sets with 110 degrees would you find pincushion magnets.

So the static magnetism to the metal bell is the only cause I can see to cause a pincushion effect on an old round metal CRT. The weird thing is that from Chris's photos the pincushion looked so uniform. Which would suggest the tube at some point in it's life must have gone through a strong uniform magnetic field.

When it was shipped, did it go through a parcel scanner to determine the box's contents?

I picked it up from an owner who bought it new almost 70 years ago. Tomorrow I’m going to do some yoke swaps to see if that makes a difference

So I should go over the metal bell correct…not do the withdraw circling from the screen

Go over the metal bell, slowly withdrawing before switching off the current.

Chris last said he was persuing alternative yokes. I cannot see how a defective yoke could physically cause the pincushioning.

To review: could Chris recap the sequence of events?

Did the origal tube work and display non pincushion?

Did the pincushion only appear on the replacement tube?

Does Chris have a degaussing coil and has there been any update?

Hey guys...sorry I've been MIA. Life showed up really intense. I'll update everything shortly. Nothing has progressed since my last update. Picture is still slightly distorted with symmetrical bends in the vertical and horizontal aspect like it's being pinched top to bottom and side to side.