UTC A-25

Raf was kind enough to send me a whole box of iron from Brazil. Included were a couple of UTC A-25 output transformers.

uhoh

I found the lam in an old Mag Met catalog:

WOW nice! :thumb:

OK, thanks again to our Brazilian friend.

Here is the print for building a UTC A-25 if your into it. This seems like it would be a very nice sounding transformer. Can't wait to try one.


This is a single plate-to-500 ohm line that will tolerate 8 ma of unbal. dc.

hiya!

Fantastic work CJ! Can you post some erotic pics?

Thanks for all the info on this UTC!

bump for the A25 , had a request for, no gory pics, looks exactly like the A24 and A26 only different, 

info that way ^^^^^^^^

Out of curiosity, what are some classic designs with a SE output stage that could use a transformer like this one, and run up to 8ma current through it?

maybe the API without the cap?

or possibly an old WE or RCA circuit,

maybe a 990 if you used the taps,

UA610, does that use a gapped xfmr?

maybe a Redd 47 without the cap and reduced plate current, that might be fun,

but you are right, far less common as the P-P or parallel fed stuff,

It would be suited to an RCA BA-2, with the multiple taps you can wire it for different ratios depending on secondary load. From Bunkerofdoom: A-25 resp.40-20K, +15dBm max level, so with about 4mA unbalanced current it should be no problem.

I hadn't looked at F lams before but now I realise that that core would be perfect for DIY transformers/chokes with small DC current, what would you expect to pay for an A-25?

EDIT: I notice that the A25 primary is close to the A19 primary, both 15K rated for 8mA but different DCR. So quite possibly they have the same lamination, maybe more turns and less lams in the A19.

Also RCA BC-2B, another RCA with one 6SJ7 like tube directly to OT (can't remember the #), redesigned Gates 7X and many others. IIRC there were some discussions about UA610 OT not being gapped. I find it interesting that many preamps with gapped transformers didn't have nfb.

UA 610, WE 121A, WE 105A,  are are single ended amps that run DC thru the pri,

Differences of the A-25 to LS-27?
CJ, putting all your transformer posts into a single reference would be incredibly awesome.
The sad thing about the wealth of knowledge on the internet will be it disappearing someday. (or else maybe it won't?)
There are gates pres with SE transformer coupled. SA-134, 7x (drawn by emrr)

oops! 

yes, Langevin needs a feedback winding and i swapped 141a for 105a,  fixed post above,

thanks emrr!  you have any RCA schemos with SE xfmr with DC?

there might be a way to simulate a feedback winding with resistors and caps on that Langevin, but phase shift can be a problem when using capacitors,

here is a site with some WeCo schematics>

http://www.audiosharing.com/archive/western/we_amp/we_amp.htm

Virtually all of the RCA are SE with DC. 

here is an application for the A-25, weird lookin amp with LED's for the cathode resistors,