Neumann n61 replacement power transformer REWIND attempted

[tardishead]

Help
Does anyone know where to get a replacement power tranny for n61

I think it's 240ac to 200v secondary with 22v heaters with centre tap

 

[chriss]

Have you already asked Microtech Gefell? They should be able to help.

 

[tardishead]

No reply from Gefell
Does anyone know anybody in uk who will rewind transformers hopefully cheaper than sowter

 

[tardishead]

I decided to have a go at rewinding the tranny. Bought myself a manual coil winder and some wire.
Well I think I have chosen a pig for a first attempt at transformer rewinding.

When I was unwinding it I measured the HT winding to be 0.15mm and I was was wondering "how did they get this so tight and uniform?" And the windings had virtually no wasted space to the edge of the bobbin.
And sure enough when I tried to rewind it myself I overfilled the bobbin window
tried a few times - nope!!!

Did those German transformer builders have special winding machines?
Does anybody have any tips?
I think my coil winder cannot go slow enough to really carefully get these thin wires uniform.

The closest I got was when I decided to wind the 0.35mm heater wires first because these are easier to get a more uniform flat platform in order to get all those tiny HT winds on. 2200 turns needed.
I read somewhere that a heater winding with a tap to ground between primary and ht secondary is a good electrostatic shield so maybe this sounds like a good idea.

So what are my options?
go thinner gauge in each of the windings.
The original wire used was good for 50ma for HT and approx 300ma for heater.
50ma is way more than you will ever need for HT on a tube condensor mic. So I figure I can half this max current  and go to SWG40 or 42 (0.12mm or 0.10mm)
However this was the winding that broke!! Or is this just a consequence of age?

EC92 is 150ma heater so I think I could use a thinner heater wire as well by one gauge

 

[zebra50]

Hi Tardishead,

Does your winder have a lateral arm for setting the horizontal spacing? The automatic winders normally have this which makes neat coils a lot easier.

Having the bobbin absolutely centred helps too.

Where are you based?

Stewart

 

[tardishead]

No my winder is super basic
Can you point me to an example of the winder you mention

Anyway after several attempts I managed to rewind the transformer
Hurray
Put it in the power supply and it works fine. So far so good

One question
When Putting the Lams back together is it customary to have the last lamm of one end inverted so varnish faces outward? Ie both ends are insulated from the clamp?But the last two Lams are shorted together in that the unvarnished sides meet together

 

[zebra50]

Glad you got it working. Here's the kind of thing I was thinking of...

http://www.youtube.com/watch?v=au_jUsoJErY
http://www.youtube.com/watch?v=NvTRvtHDXkI

The lateral arm motion is synchronised to the rotation, so that you can adjust the spacing between each turn of wire.
Cheers!