[Amps] HV Transformer

[Steve Wright]

On 04/02/16 06:00, Bryan Swadener <bswadener at yahoo.com> wrote:
> Until I rewound my first xfmr back in the 1980s (HV to LV, 750VA),?
> I also used to think it was difficult.

Yeah it's not that it's difficult, it's just time consuming and some 
thinking ahead is required.  You will be cutting up bits of wood and 
drilling holes to make mandrels, and so on.  It's all just plain ol' 
workshop backyard stuff, and if you've never done this sort of thing 
before, just be patient and give it a spin.

> Thanks go to Manfred XQ2FOD and his info on his website
Without Manfred's excellent spreadsheet and competent guidance I doubt 
I'd have had the confidence to attempt it.  I've since done five or more 
transformers, the largest of which expertly destroyed a 25A primary fuse 
in the 230VAC circuit when I wired the diode rectifier incorrectly..

> A transformer shop in OR had the NMN (Nomex-Mylar-Nomex) paper
> I needed, and a local shop vacuum-pressure "varnish" (actually,
> polyester) impregnated it free-gratis. The salvaged xfmr cost zero.
> My investment was about?$100 for a spool of HML (heavy
> polyimide-coated) 18ga wire and 3X the?needed NMN paper.?
The local motor-rewinder makes a lot of money out of large 
multi-million-dollar projects, and they were very enthusiastic about my 
attempts to build ham-radio gadgets, and consequently I have only 
managed to slip them a $20 note by all manner of sly methods!  They 
grinned and would not take my money at all!

I have resisted the temptation to buy a large spool of wire, since I'd 
have to pay good money for it, and Manfreds' excellent spreadsheet was 
adamant that I should use the CORRECT size wire please!!  So I so, for 
no charge... ;)

My point being, this list now has a few rewinders who have 'done it 
before', including a couple of experts.  If a few more people gave it a 
whack then this pivotal part of tube amps might be a lot more accessible.



Steve
ZL1BHD