I need a pair of very large output transformers for a 165 watt push-pull tube amplifiers......These transformers need to have insulation for 1000 volts, Primary of 6.5 K, A special output winding at 4 ohms for feed-back......And be of at least peer-less quality........Probably around 15 pounds...........Anybody know anybody that has that or can build it ???    THANKS 
I have had custom transformers wound for me for tube amplifiers many times, Will.  I've had the best experiences with Edcor and Classic Tone / Magnetic Components.  Some of that depends on whether you prefer plastic or paper bobbins.  Heyboer is also a decent choice, though I prefer the other two.  Folks recommended Merren to me, but I have no experience with them.  I used to think Weber fit the bill as well, but found out their transformers are imported, so custom work is unlikely, and in your case, I cannot see it happening. Though Canadian, you might look into Hammond, which offers off the shelf units, and make some pretty big iron which might suit you.  Due to the exorbitant cost of shipping, I otherwise avoid foreign outfits.

For what it's worth, there are more expensive / upscale like Mercury Magnetics, and even more esoteric outfits like Electra-Print, and Dynaquest.  Honestly, I don't recommend going that route.

Just out of curiosity, do you need a UL tap?
Trelja:  I have been working on this for quite some time...I'm a little surprised at how difficult this really is.....First let me say , no ultra-linear taps.....Here are the main problems I'm running into on this, First having insulation over 1000 volts....., second being able to work at 150 watts....and have reasonable frequency response 30hz-20k......and have a separate winding for feed-back.....So transformer people can do one or the other but don't seem to be able to do it all..........Hammond cannot make it, Heyboer can make it if they have a old one to reverse engineer....I've not had good experience with Mercury Magnetics.....I can't get a hold of anyone at Magnequest or Electro-Print, which is probably good because of price........I will be calling Edcor in the morning and talking to them.....Any other input you can make will be welcome.....Will   
@autospec Will, please give Classic Tone Transformers a call as well. Both they and Edcor do custom work, and take those needs seriously. Heyboer also seemed willing, but again, my results with them fall behind the other two. The rub I had with Edcor was in setting up an account, I needed to provide them far more (government issued information - federal and state tax IDs on official letterhead) than I did with any entity I’ve ever dealt with to prove I was not just a hobbyist. I have my own thoughts on the more esoteric winders as well as ultralinear taps, but I’ll hold them for now.

In regard to your feedback winding, is it possible they get tripped up by your nomenclature? Are you actually requesting a completely separate winding, or just the typical 4 ohm tap to run your feedback loop off? If the latter, they churn them out that way all day long, and should add but a couple of dollars to a single tap output transformer. A separate output winding would be different than most audio or guitar output transformers even if their power transformers get built that way, and my question then becomes, do you truly need a solution that elaborate?

Trelja:    I ordered and received (4) of these out-put transformer from Edcor.....They look to be rather quality built........I have installed one in a 165 watt Altec Lansing 1570 power amplifier without issues.....I will be running some "square wave tests"  and at this point very happy with these transformers.............I had used them before , I thought maybe this might be to difficult for them, but after you mentioned them I figured to give them a try.............Will
@autospec thank you for following up, Will. Unfortunately, it happens so rarely.

I'm really happy Edcor could seemingly provide what you wanted.  Hopefully, they work out as you want
@autospec  I am very interested to hear your findings and know your opinion of these Edcor transformers.  I have a pair of Altec 1570Bs.  One has the original transformer and the other does not.  The replacement tranny in the one sounds fine, but it is going to melt if I run the amp beyond said transformer's 100W rating.  Thanks!!
Sir:    I have had good results ,but I haven't done a square wave test yet.....I plan on doing that ...  I now have a spare Altec transformer that I may be willing to sell you also.....If you would look at some of my listing on Audiogon, you will see my phone number....Please feel free to call me........Thanks Will
@autospec, apologies for my late reply, I didn't have email notifications set correctly and got slammed with work, I will dig your number out of your listings to discuss the spare transformer. Thanks!   -Sam