UTC A-10 transformer need help!! CJ??

Hi.

I bought an old UTC A-10 on EBay a few years ago for my LA2A project.
When i finally got things moving this year it seemed that the transformer was bad.
With a tip from CJ I took the transformer apart with a heat gun!
There were no fragile leads coming out of the transformer to repair, just cloth covered cables.

My question is what faults to look for.
And what should the resistance be between the (10) leads??




Regards,
Dennis

Sorry to stray off topic with helping you, but is there someone doing FAITHFUL/ACCURATE reproductions of these and the A24's? If not, why not? There's obviously a market for it with the insane prices these are fetching on the eBay.

I seem to recall Sowter, Lundahl, and Cinemag doing versions, but I've not heard how similar they are to the originals.


T

A man of my heart!
See, it ain't that hard to hack a tranny.

Those black ones are quite rare.
Different core I believe. Same coils.
Less henries, probably 50/50 intead of 80 super.



A-24 ain't tatt great, unless you like a 40 k rolloff for mellow vocals.

Hmm, A-24 has better high frequency spec than the A-10. Not sure where we're going with this info.

newer A-10 is +/- 2db 20-20kHz. I've never thought they sounded that good when compared to the LS-10. They are getting a little too close in price to one another, given the differences. I've had a half dozen of them side by side and found them all to sound a little different from one another.
This black one shown here is specified at +/- 2db 30-20kHz in a late 1930's catalog. This style appears to have been used at least until 1945, and maybe up until 1950. Anyone know when they went to the later case and terminal style?

A-24 is +/- 2db 20-40kHz. It should come out better than specified in an LA-2A since it's being driven with a much lower impedance than required to achieve said spec. There's one on ebay this week approaching the price of an LS-50, which is +/- 1db 10-40kHz and 8dbm more headroom.

PS: Sorry I'm of no real help to you, API. Maybe this info will help someone.

You have to sweep them to get the real beef.

the 20-20k blanket spec is more of a generalization than anything else.
sweepinfg with different loads will yield different curves.

LS-10 is nice, but you have more core to magnetize, which means more core loss.
If you do not need the extra headroom, then a smaller core is a better choice.

Hmm, an LS-10 always sounds better to me with a mic into an unloaded grid than an A-10. A-10 sounds like a tiny midrangy POS in a side by side comparison. But, that makes an A-10 great for distorted guitars. :grin:

And in the context of an LA-2A in a modern studio, the A-10 is being driven with WAY more level than anticipated when the LA-2A was designed, and I'd image the LS-10 would eat the A-10 for lunch in performance there. If the specs are to be believed, and useful at all, that extra 8dbm jump from +15 to +23 will make the difference in good bass performance when fed from the standard +18 output of many digital recorders. But, we get the trade-off of a 'non-original' sound.

The 40K vs 20K on the top of the A-24 and A-10 must mean something, if they were making that guarantee. They published typical sweep charts in the catalog, for god's sake. Of course they vary with load and source impedances, as I pointed out with the lower-Z drive the A-24 sees in the LA-2A output.

The higher 30Hz figure on the oldest varieties jive with your observations about the increase in nickel on the last versions. They probably made an improvement in that direction once previously with these oldest smaller case types too.


Now tear down an LS-10 and prove me wrong by saying the core and windings are the same as the A-10! I really want to know what the difference is, now that you've got the A-10 and the HA-100 as the same iron. No, I don't have one to donate. Any blown LS-10's out there anyone?

Sorry again Dennis, I'm way off your thread again. Do you have any DC measurements that match CJ's chart?

Hi.

Looks like everyone wants to hijack my threads this week!!

Excuse me, but i know how to handle a heat gun, but i do not know how to measure the DC resistance in a transformer!!
There are 9 leads coming out, teach me how to use them!!

Regards,
Dennis

put one ohm meter lead on a transformer lead, look for resistance to any other lead, or leads, make note of it. Move on from lead to lead until you have a drawing of the windings with the various resistances between them.
Look for the standard UTC winding chart, and make notes on a copy of that. Once you're done, compare to the resistances on CJ's chart. Anything missing is an open winding. Anything too radically different is a failing winding.

Pins 1-2-4 and 3-5-6 are the pri's.
7-9 and 8-10 are the sec's.
Pin 11 is shield/case/core ground.

Pri leads all break out from the same side if I remember correctly.
So do the sec's, so ohms out the side of the coil that has four leads.
There will be an extra shield wire in there somewhere.

I believe the LS-10 coil is same as A-10, only bigger.
Doc Hoyer has the winding data, but every time I ask, he can't find it, as he has been
hacking for over 50 years and has three file cainets full of winding data.
LS-10 X has more shielding than the A series.
Big cans were expensive to make, but they look nice.
Later models switched to a cheaper can.

Only difference is the LS uses the bigger 4-L lam (mag met) that is found in most of the LS series input transformers.

Both are dual coil affairs with 9000:900 turns, split secondaries (two pies, wound sisde by side at the same time, a UTC trade secret miracle, how they got those turns on there. Very rectangular, no sponges)

pins 1-2 and 5-6 make a 16 ohm input for moving coils?

Here are some canibal shots of an LS-26 that I forgot I hacked. I was
gonna thread it, but never got around, not that popular of
a transformer:

http://vacuumbrain.com/The_Lab/TA/UTC/LS_Series/LS_26

Wow, that's really perverted!

I love those bridging to grid types for limiters and line amps. You don't see them very much.

I got a new hs-29 sittin at home waiting for a Pultec chassis.
Those guys are nice.
I hacked that one also, there is a thread around here somewhere.

Speaking of LS-10X, I have never seen a "no bid" after 8 days,
don't tell anybody, but look:

UTC

private auction, doh, no wonder no bids.

Ok, i think i have learnt something here!
This is what i have found out.

Primary:
Coil 1 pin 1 - 4 35,2 ohm
Coil 2 pin 3-6 33,1 ohm

Secondary:
Coil 1 pin 7 - 9 2550 ohm
Coil 2 pin 8 -10 2390 ohm

So, it does not line up with CJ´s chart.
Or have i done something wrong??

I get no connection between the primary and secondary, is that right??
Think so.

Does this look like a healthy transformer??

Dennis

Looks good to me... numbers seem to agree with CJ's pinouts.

Keith

Yes, looks good. You can expect the one you have to show different readings.

So why did you think it was bad?

You do know that 3-4 have to be tied together and 8 - 9 also?

Always check resistance before moving on to disassembly!

Put it back together and slap it on that limiter!

Hi.

Thanks for your help!

The reason i thought it was bad was because i got no input (or output) at all when i had it in my finished LA2A.
And from ememory i did not get these readings when it was in there, thats why i took it apart.
I suspect that there could be a short somewhere in a cable, because when i first had it out i got a reading of over 200kohm on the first primary coil.

So i will put it carefully back together and see what happens.

But just to clearify, there should be no reading at all between the primary and secondary???

Regards,
Dennis

No connection. Look at the symbol for a transformer, that should clue you in. It's why they're used for isolation.

Keith

I should have known!
I am learning everyday, thanks guys!

Now i only have to figure out why there is no signal coming into my LA2A.

Dennis

Now i only have to figure out why there is no signal coming into my LA2A.

Click to expand...

You probably wired the transformer wrong...

Try looking at the utc specsheets, with pinnings.

Hi again.

No, i had not wired it wrong.
There is signal going through the transformer (and the whole compressor!).
But on the other side of the input transformer the signal is quite weaker than what i put in.
Is that normal??
Also after the output transformer the signal is very weak.
And also, no needle movement and no compression.
Will post some questions in the LA2A thread!

Thanks for all help!

Regards,
Dennis