winding a sort of 2503 type output tranny . . . .

So I got my parts from Ferrous Maximus (CJ) and am ready to wind the first one. I found some trifilar 34 guage magnet wire at a local surplus joint, so that's what I'm going to try to use (I wasn't going to use the meter winding on my APIs anyway). Questions:

1) How much tension should I try to keep on the wire as I wind (or the corollary, how loose is too loose)?

2) Given that I'll have only three wires of smaller guage, how many more turns should I put on than the "real" one's 276? I know DCR will be higher, but L will also go up which wouldn't be bad. What about stray capacitance? How can I determine approximate bounds for the number of turns given that it will be used on an API mic pre?

3) I thought I saw a winding calculator somewhere around here, but I can't find it. I seem to remember it taking wire guage and maybe bobbin dimensions and giving an estimate of # turns, inductance, and DCR. Or maybe I dreamt it all up. I couldn't find it in the transformer meta or with searches. Help?

Looking forward to getting started! Thanks for any help.

A P

1) Don't sweat the tension, just don't break the wire or stretch it.
2) I would fill the coil up all the way. Leave some room for the wrapper and lead and tape. Don't force the last lam, easy to slice wires if you slip it sideways. Leave the last lam out if too tight.

Easier to unwind and rewire than to splice more magnet wire on.
3) You can measure the capacitance with an ordinary cap checker.

I posted an excel calculator if thats whay your talking about.
I will dig it up at the next coffee break.

Is your house still on the hill?
Do a search on Love Creek Mudslide if you want to read something spooky.

cj

Thanks, CJ.

1) OK on the tight part, but I'm concerned that I may be winding too loose. How loose is too loose?

You excel calculator may be what I remember. I'll try another search.

My house is fine, though we had some pretty awful wind this past weekend. Thanks for asking. Lots of limbs on the driveway, but no trees down (yet). Lots of small to medium sized slides on the roads. One completely blocked Bear Creek Rd. for most of Saturday--maybe 30-50 yards of mud/rock, several trees, phone lines, and power lines all jumbled up on the road. Just in December I've measured over 23 inches of rainfall at my house (normally we get about 50-60 between October and May). We had 11 inches in 36 hours the weekend before Christmas. We need a break!

Did you have any trouble in the valley? I had to work Monday and it rained hard down here most of the day.

Cheers,
A P

p.s. I know about Love Creek. Not good.

[quote author="CJ"] ... But, you guys have to slice the gray sleeve and pull out the wire.
Four matching pairs is perfect for this xfmr.
Right gauge also.[/quote]
:shock:
Cat5 cable ??

I vote Cat5

I finally found a solid 2 hour chunk of uninterrupted time to try my hand at winding one of these things. Pics will come later (sorry :sad. I used 3x34 trifilar magnet wire that I found at a surplus shop. My winding setup was pretty, uh, primitive to say the least. But it worked. I got enough tension on the wire to make me feel confident that I wasn't winding too loose, but not so much that I felt like I was stretching the wire.

I piled it on leaving myself a little clearance for tape up and wrapping at the end. I got 30 turns per layer on the bobbin and did 22 2/3 layers for 680 turns overall. Why didn't I do the last 1/3 layer? I don't know. After hand winding that many turns my brain was a bit fried. I should have gone to 690 turns. I also might have gotten another layer or two on, but I figured I was getting pretty far from "real" 2503 land already.

I did make a few measurements. DCR of a single winding is 50ohms (one came out 47ohms so I guess one strand was slightly thicker than the other two). With no lams (air core) I measured 8.12mH on one winding using a cheap-O BelMerit digital LC meter.

I'm not sure I did the leakage capacitance measurement correctly. I connected my LC meter probes to two starts and left the two finish ends floating. With this arrangement I measured 9.9nF on adajacent strands and 6.7nF on the outer strands of the trifalar (flat) set. Make sense?

Tonight I'll finish up the lead breakouts, wrap it, and lace up the lams. If anyone has any pointers on how to measure other parameters of interest, I'd appreciate it. I'm curious how this bastardized thing compares to a real 2503. Anyone (CJ) have measurements? I can't really do anything with it yet as I'm still stuffing my Fabio 312s. I'll try to get some pics up this week. Thanks to CJ for kicking this project off. Fun stuff!

A P

Pics and the rest of the story are on this thread in the lab.

I just got a package from COSMO corp. I order two samples of bobbins. I open the box and they sent me 6 of each. Slots/no slots. Some time in the future I will try to wind me own. Until then I will have to rely on others. But this looks fairly straight foward. Thanks CJ for the links.

Joe