Thomas electronics is a military supplier. They were mentioned in a thread here in 2014. There does not seem to be any progress in working with them, probably because of both price and the fact that people were looking for someone who could repair pyrex glass tubes. They might be an option if you have a regular glass tube and megabucks.

Thanks for the kind words. I tried mixing India ink into epoxy but that didn't work, probably because the ink is water based and didn't mix well. Also, the epoxy didn't get hard enough to be able to be used as a resistance track, even without anything added. Next I tried adding ground up pencil lead to lacquer, but that didn't work either. I could have tried getting powdered graphite and adding that to lacquer again, but I didn't want to go through waiting for that to arrive, so I went back with my old idea of pencil lead rubbed onto a suitable surface. I initially used card stock for a trial and got a strip which measured almost exactly 5MEG, but since this part dissipates a bit of heat I didn't feel it was a good idea. That's when I started looking for a thin phenolic sheet. I got one that was .020" thickness and looks like thin PC board material. I roughed up the surface a bit with fine sandpaper and rubbed the pencil on it until I got close to the correct resistance. It really didn't take a whole lot of pencil rubbing to get there, and you could see light through it.

I knew they were more of a military supplier but it seems from the literature they would take jobs, then again, as you pointed out, it could cost a lot. Even so, i figured it was good to mentioned them. Hopefully the ETF people will get a handle for this and perhaps in the future, there will be a small demand for it for others to pop up much like there is a small resurgence in vinyl records. I do see the point though where predicting the future is tough, but who knows, maybe once 3D printing gets more sophisticated. :scratch2:

:thmbsp:Keep up the good work! If I hit the powerball, I'd like to be trained for this and join in.

I spoke with them extensively back in 2014/15. They claim they are capable of rebuilding anything including Pyrex tubes although never provided evidence of this, and that's as far as it went. They would never commit to anything for any price. They basically had no interest in our community. Perhaps someone else could pickup the torch and try contacting them.

Darryl

I was in touch with them too a few years ago. Ultimately no result. Like Darryl, I don't think they're interested in folk like us.

With a place like that, would you really want to trust them with ultra rare, virtually irreplaceable, roundie CRTs? Given that they have never done them before, and don't even seem to care to try?

Yeah, hopefully by the time when our demand will be higher, the ETF people can take care of us. I guess like with anything else, I'm sure Thomas would do it for the right price, everybody has their price as my father says. The thing is, it depends if we can pay for it. ;) I was always a big believer in "when the door is closed, God (or whomever/whatever you believe in) opens a window" but sometimes opening a window takes action on our part too.

Right now I am trying to deal with the failed vertical convergence transformer. I was not able to get a turns count due to damaged wires, and I gave up after unwinding over 6000 turns of wire which kept breaking due to corrosion. The primary was still good and I was able to get a resistance reading from that winding, but the secondary was open and I don't know a whole lot about it. The wire sizes on both windings measure the same (.003") which corresponds to a 41AWG wire. Knowing the wire resistance, winding resistance, and the approximate turns per foot of wire I get 2000 turns for the primary which would seem about right. Unfortunately the secondary resistance measurements given on the Westinghouse schematic are incorrect. Since the Sams folder on this model gives an RCA part number for this transformer as being the same as that used in the CT-100, I looked at that schematic and found very different resistance measurements as well as in the Sams folder on this set. I'm really not sure what to go with here. Also, the ratio on the secondary winding either side of the tap doesn't jive with what I know about the AC voltage requirements given on the 15GP22 datasheet. The datasheet gives a convergence/focus voltage ratio of 900:225, or 4:1, but the transformer looks more like 2.5:1 based on the resistance readings given.

Have you tried contacting Steve McVoy, who possibly could lead you to someone who has done this before and knows the turn count?

John Folsom and John Yurkon come to mind.

While waiting for information on the convergence transformer data I decided to do the IF and chroma alignment. The video/chroma was pretty close as-is with just a little adjustment needed. The IF is a different story, however. It had a narrow peak instead of the double hump broadband response shown in the service data. I was having problems with the cores sticking in the IF transformers and I ended up twisting the coil form in the second IF can. I had to remove the transformer and get the cores out and do the surgery on the broken wires. As of this morning I have the repaired transformer installed but not connected. The third and fourth transformers will have to have the cans removed so I can remove the metal clips that engage the cores and try to get them back into their places.

The marker in the center of the scope screen is 44MHz.
The second shot is the chroma response to the demodulator input and is pretty close to what is called for in the service information.

Here are the DC resistances of the vertical convergence transformer. These readingx are taken directly from a known good trans that I removed from my CT100 and replaced with one of the replacement transformers that Folsom had for sale back in the day. The original has been sitting on my shelf for about 10 years because I am saving it in case of a failure in one of my 15" color sets.

The resistance of the primary is 1060 ohms.

The secondary is 20,300 ohms center tap to one end.
and 8700 ohms center tap to the other end
with an overall end to end resistance of 29,000 ohms.

That equates to about 27,645 feet (5.23 miles) of #40 wire on the secondary at 1049 ohms per 1000 feet of wire.

Hope this helps in your winding effort in the event you are unable to obtain a replacement.

Good Luck!

Thanks much for the information. I guess the Westinghouse and RCA transformers, although functionally equivalent, are actually constructed differently. Looking at the ad on the ETF website for the reproduction transformers, it says that 41 and 43AWG wires are used in the windings. My transformer had only 41AWG wire in both primary and secondary. The scan of the Sams folder for the Westinghouse shows secondary resistance readings of 3800 and 9200 ohms (although the scan is fuzzy in that area, so that's a best guess) whereas the RCA part as you measured is 8700 and 20300 ohms, respectively. The primary resistances are just about equal, however. My educated guess is the RCA part uses 43AWG wire on the secondary. 41AWG wire is about 1320 ohms/Kft and 43AWG is about 2140 ohms/Kft, quite a bit of difference. Using best guess turns per foot based on the location of the windings the primary is 2000 turns of 41AWG, and the secondary is 8700 + 17000 turns of 43AWG. For the Westinghouse part I get 2000 turns of 41AWG and 5750 + 12500 turns of 41AWG. Using the same insulation thickness the overall winding dimensions are roughly equal and just about fit in the E laminations.

The overall primary/secondary ratio looks to be different between these two if my assumptions and calculations are correct, but the tapped secondary ratios are nearly the same.

I don't know if I want to attempt this on my own or see if maybe Edcor or some other transformer company could produce this.

If you order them from a professional transformer company I'd be interested in 1-2 vertical transformers.
If John Folsom was ordering the reproductions from a reputable firm he may have proven exact specs from the company that you can use.

Forget about the resistance numbers on the Westy schematic. They are wrong. The correct numbers are on the CT100 Sams schematic. I have no first hand knowledge of the correct wire gauges, but I would go with the numbers on the ETF ad for Folsoms trans. What do you come up with when you measure the actual wire from your trans?

Yeah, I know the Westinghouse schematic numbers are wrong (1350 ohms for the secondary IIRC). Since the CT-100 part looks like it works in this set as well I'll go with the numbers I get based off of your information. I did measure a 1 foot piece of wire and got 1.3 ohms which corresponds with the 1320 or so ohms per 1000 feet of 41AWG. 43AWG should have been more like 2.1 ohms per foot. That's why I believe the parts were made differently.

My secondaries were open so I didn't have the benefit of getting a resistance reading off of the original part.

I was finally able to do the IF alignment after dealing with stuck and chipped cores and two transformers with broken wires. I think I got a pretty passable response after a lot of iteration. Hopefully the color will look and sync better now. I will need to order more capacitors so I can replace the remaining paper wax capacitors still being used. Also I will need to check out the horizontal oscillator since it starts becoming flaky after being on for a while, shifting frequency a bit then back again. I need to build a 3.58MHz crystal oscillator for aligning the demodulator section. That way I should be able to set up the 90 degree phase shift using a dual trace scope and be sure it's correct before installing the CRT to the chassis. That is the pain in the rear about this set... the CRT has to be removed from the chassis to do much of anything with it beyond normal adjustments.

Looks like I'm on my own as far as the convergence transformer goes, so I ordered one of those Chinese automatic coil winders and some 41AWG wire. This should make it easier to get a nice, tight, even wind and if the transformer ends up not working for some reason I can try again fairly easily. I'll first try winding the primary and see how close to 1000 ohms I get for winding resistance. That's a few days off right now. I also need to order more .1uF capacitors, and I will also get a 3.58MHz crystal oscillator for chroma demodulator alignment. My work area is in the garage, and with this 100 degree weather I'm not really doing much now.

I wish you success with the attempt.

Dumb question: why can't you use the internal 3.58 oscillator to do the 90 degree adjustment?

Pretty sure Westinghouse didn't use a crystal referenced oscillator In that model so unless you are synched to a color burst it will probably drift off frequency.

Not a dumb question, because this particular set does not use a 3.58MHz crystal controlled oscillator like pretty much everything else. It's a bit more like a horizontal sweep oscillator AFC circuit controlling a reactance tube based off of the color burst and it actually has a control labeled "color hold". Guess that's why the alignment instructions call for an external crystal oscillator.

I knew it used an LC oscillator, but if you first adjust the oscillator and have it locked properly to an incoming signal, then it should be just fine for adjusting the 90 degree transformer.

By the way, I don't know why the designers used a tuned transformer to get a 90 degree phase shift. Better to use the transformer to get the impedance match needed (as they do), but not for the phase shift. The R-Y demod drive goes directly to the burst phase detector, so R-Y drive phase is stable at 90 degrees to the burst. Why not then use a simple RC circuit to get the additional 90 degrees for B-Y drive? It would not need tuning to obtain the correct and much more stable angle.

I have the winding machine here now. I did a test wind of one layer, 333 turns of 41AWG wire and it turned out very well. Now I'm waiting for the Kapton tape to get here. The machine did the 333 turns in well under a minute. I'm going to try the winding data I calculated for the Westinghouse part since it uses only 41AWG wire and see how it measures as far as winding resistance. It should not take a whole lot of time to wind the transformer with this machine.

If all goes well I will order some 43AWG wire and try to do the CT100 winding data as well. 43AWG wire is more expensive than the thicker, more usual gauges.

:thmbsp:

I measured the resistance of the 333 turn layer a bit later last night and it was 175 ohms. This calculates to 1050 ohms for the 2000 turns which is close enough to the original 1000 ohms.

Post a photo of the coil winding machine.

This is the same machine I have

https://youtu.be/7PXXoA3897M

I tried winding the replacement transformer, but my first two attempts were failures. The first one wound ok, but two of the free wire ends broke off and could not be retrieved. The second time I slowed down the winding speed and got most of the way through but started having problems with wire breakage because the wire was snagging on mold flashing on the edge of the wire spool. I did end up finishing the part and got the wire leads attached. One of the wires broke because the coil was too much of a tight fit to the lamination stack, so that one also became scrap. Now I need another spool of wire to continue. I did another test wind of the primary only and it seems to be ok, but I will need more wire to do the secondary. I'm new to this and am learning what works and what doesn't as far as securing the free wire ends and getting an even layer of wire to lay down. I also will make the bobbin a bit shorter than the core window so it hopefully will fit after all the windings have been laid down. I'll get this right eventually.

John Folsom was kind enough to give me a copy of the winding data for the replacement transformers that he had made available. Good news is my own calculations were close enough to have resulted in a working part if my first two attempts had succeeded. No 43AWG wire was used, so the winding resistances should be close to the Westinghouse part. Now I just need to wait for the new spool of wire to get here and start practicing with the machine again. I tried two more test winds of the primary which appeared to have turned out OK, but that one is easy since it's only a few layers of wire. The problems start with the secondary simply due to the number of layers of wire and insulating tape needed. Just a bit of unevenness from a wrinkle or air bubble seems to get magnified when winding the new layer over it. I probably won't get it 100% perfect, but I think I can get it close, at least enough to recreate the transformer. Apart from a few wax capacitors, the transformer is the last hurdle I have at this time to getting this set running again barring any unforeseen problems.

:thmbsp:

I did get the transformer working, at least for about a half hour before I heard the sound of insulation breakdown. I did at least get to see the results of the IF and chroma bandpass alignment I had performed. Much better detail and color quality than before. Back to the drawing board on that transformer, though. I was trying to do the convergence procedure when the transformer went bad on me, so I didn't get the chance to take any pictures.

I need to find something for winding layer insulation that has a bit of grip to it so the windings don't move around so much. Kapton is good for insulating the inside and outside of the windings as well as between primary and secondary, but is too slick to hold the individual layers. Double sided tape is too thick for this purpose as it will result in a coil which will not fit in the core window. I used fiberglass resin in a glass jar under vacuum for impregnating, it seemed to work but is too thick, also expensive since I had to throw away over 90% of the material afterwards. I could try something like good old Minwax polyurethane and hope it will cure all the way through. At least the unused portion can be saved. This has been an interesting, although a bit costly learning experience. I would like to try doing some audio output transformers later on down the road with what I have learned so far.

That winding machine looks expensive.

Yes or no depending on how you look at it. It sells for just under $600. It looks to do a pretty good job of laying down an even layer of wire. It's certainly not as good as a much more expensive machine, but for small production runs it will do fine. Materials and construction technique are just as important as getting an even layer of wire on the bobbin. The main weaknesses are the tensioning system and the wire guides, but those could be improved with a bit of ingenuity and work. The basic machine itself is pretty solid otherwise.

I developed a process for doing the vacuum impregnation which I detailed on audiokarma, have a look here:

https://audiokarma.org/forums/index....t-home.859083/

Results have been extremely good, and I wouldn't hesitate to recommend this method.

Thanks a lot for the information! I was thinking of thinning the varnish with mineral spirits so it would be thin enough to get inside the windings and insulation. I first need to find a suitable tape for winding layer insulation. I used Kapton the first time around, but it's a bit pricey, has to be ordered in, and wires just slide all over it easily. Masking tape is too thick (5 mil), so I need to use something like regular old Scotch tape. The secondary is the tricky part since it carries 3KV or so of DC and up to 1KV of AC on top of that, and that's in very thin 41AWG wire.

I already have the equipment for doing the impregnation, just need to try again. I really didn't pull a vacuum as long as I needed to since the resin I used had a relatively short work time and I didn't want to end up with a big block of resin with a transformer in it.

Rather than thinning the varnish, try pre-heating it to reduce viscocity, and also making sure the transformer is well heated to expel moisture. Read through the procedure I linked to, the steps and heating were all based on trial and error - I tried a bunch of iterations to get to that. Long working time of varnish is a good thing. After you're done, unused varnish can be put back into the can and used later.

As for wires sliding all over kapton, why not use something like spray on 3M adhesive to make it a little bit tacky before installing it? Just a light dusting should be enough to hold the wires in place.

If one of the better materials to insulate between layers is too thick, maybe you could use it every other layer to get it's advantages and reduce thickness.

I can get 3M type 56 tape from Mouser, so I'll go with that on my next attempt. I attempted to wind the secondary without insulating tape between the layers because I was running low on tape at the time. The problem is the wire at the edges of the layers start moving out of place during winding of subsequent layers because there is nothing holding them in place. At least using tape between layers does hold the wires in place. There are 69 layers in the secondary, so keeping them in place without tape layers will be hard. Also I need to come up with a way to keep distance from the free wire ends of the windings and the winding layers themselves to avoid breakdown there.