Two Way Hourglass Bends on My KCS47

[Chris K]

Originally Posted by Kevin Kuehn

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.

[Kevin Kuehn]

Originally Posted by Chris K

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.

[Electronic M]

Originally Posted by Chris K

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.

[Chris K]

Originally Posted by Kevin Kuehn

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.

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

[Chris K]

Originally Posted by Electronic M

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

[Penthode]

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

[Chris K]

Originally Posted by Penthode

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.

[Penthode]

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.

[Chris K]

Originally Posted by Penthode

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

[Electronic M]

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.

[Chris K]

Thank you Tom

[Chris K]

Originally Posted by Electronic M

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..."?

[old_tv_nut]

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?

[Chris K]

Here is the effect again

[Penthode]

Originally Posted by old_tv_nut

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.