Another Westinghouse H840CK15

[maxhifi]

Originally Posted by trinescope

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.

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.

[trinescope]

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.

[maxhifi]

Originally Posted by trinescope

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.

[Electronic M]

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.

[trinescope]

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.

[etype2]

At 8:00, this Chinese video shows the taping process. https://youtu.be/QsQ0GRR2yr8

[Sandy G]

In a former life, I worked in the Graphic Arts industry-We had a Gravure Printing plant. Trust me, go to a larger town, & locate a graphic arts supply house, & ask to see the 3M representative. They make tapes for every conceivable use & purpose-They very well could make one that is super thin. & you could be all set. Down here in the South, we have "Dillard's-If its Paper", but trust me, they'll have something. Another place to try might be a commercial electric/electronic supply house, say like W.W. Grainger's-They're nationwide, have an incredible supply line, often you go in there, tell the guy what you want/need, 10 minutes later, you're on yr way home., what you need in yr hot little hand.. ANOTHER place to try is McMaster-Carr, they have at least ONE example of EVERYTHING that was ever made-I ain't kiddin'... I can even remember the phone # of the Atlanta branch-404-346-7000, they work best if you have their catalog, but get one-Every Budding Mad Scientist/ol' electronics Junkie orta have at least one..Grainger's catalog is called the "Motorbook", I think you could order a electric motor that would run the Panama Canal lock gates.. Might take 'em a week or 2, but if you gots the Money, Honey, THEY gots the Time-And the Motor... Grainger's book is made out of Bible thin paper, McMaster-Carr's is a lot better to touch, feel, & use, to me..

[Kevin Kuehn]

Ordinary Mylar packing tape is a possibility, problem being cutting it to a custom width. I wonder if one could use a thin Cyanoacrylate glue to tack each layer at the ends? All you'll need is a couple tiny drops and that stuff will wick in a long ways. It will set almost instantly. Recommend a good hobby shop grade and not the cheap watered down variety store brands. Be cautious that if you heat CA glue with a soldering iron it can give off poisonous gas. Several years ago I got some yellow transformer winding tape from a place in Florida. It's available in any thickness you could want and they would cut it to custom widths. Back when I got mine they offered free engineering samples of off the shelf rolls.

[trinescope]

I finally got the materials together to wind another transformer. This time I resorted to buying tape off Ebay since I was able to get it in 30mm width which was close to what I wanted. 1 1/4 inch would have been more ideal, but I think this will work. The winding resistances check out OK and there is tape between each winding layer this time. I did my best attempt at vacuum impregnating the assembled transformer with spar polyurethane. Just for fun I measured the inductance; primary is 7H and the overall secondary is 500H. Quite a bit of inductance there. I will put heat shrink on the secondary leads where they pass through a hole in the chassis. It's not the prettiest looking thing but hopefully it will work out OK this time.

[trinescope]

Here is a picture of the finished transformer. For some reason my phone will not let me post pictures from the file storage so I could only get this one of the part as it is now.

[maxhifi]

Looks fantastic, fingers crossed that it works just as well!

Give it lots of time to fully dry - a couple weeks wouldn't be overkill, the varnish dries on the outside a lot faster than on the inside.

[etype2]

Nice work. Looking forward to the results.

[trinescope]

Here are the other pictures I could not post last night. Go figure, wait a day and everything starts working again.

[trinescope]

The convergence transformer is holding up OK. However, the front panel convergence control does not have enough range (not enough DC voltage), so I will need to replace the 100MEG resistor in the HV cage. Other than that it seems to work OK. Last thing I'll do is the chroma matrix adjustment procedure to get that up to spec.

[etype2]

I’m glad the VCT is holding up, good work! The color bars look better.