Univox U-45B output transformer-???

[DocGeorge]

I bought a Univox U-45B a while ago- I have wanted one for years, ever since I played through one- BUT when I got it (via ebay) the output transformer was shot. Does ANYONE know what make and model of transformer this is? (It is totally unmarked!) According to the schematic, the input impedence is 17k. I was going to rewind it myself, BUT I have never rewound a transformer, and IF I can find a real replacement, I would rather do so. Various people have recommended using a generic replacement, saying that it wouldn't make any difference, bit I know that that isn't so. IF any of you have played through a U-45B, you know why I want to get this right. Thanks for any help...talk to ya....

Doc George

[BobB]

I used a Hammond 125-H
The Imp. matches and it's the same size.

Bob

[mykey]

I bought a Univox U-45B a while ago- I have wanted one for years, ever since I played through one- BUT when I got it (via ebay) the output transformer was shot. Does ANYONE know what make and model of transformer this is? (It is totally unmarked!) According to the schematic, the input impedence is 17k. I was going to rewind it myself, BUT I have never rewound a transformer, and IF I can find a real replacement, I would rather do so. Various people have recommended using a generic replacement, saying that it wouldn't make any difference, bit I know that that isn't so. IF any of you have played through a U-45B, you know why I want to get this right. Thanks for any help...talk to ya....

Doc George

you can try to contact UNICORD for parts, but the Hammond tranny works just fine.
http://www.univox.org/ but don't know if unicord is still in business. that's all i know
for now.

[DocGeorge]

STILL looking for specs on output xformer!!!

A number of transformers would "work" in this application, BUT I want this thing to sound as good as it can, not just operate. IF Univox had figured that a 10k input impedence would work properly, they would have specified it. (BTW, I already belong to Univox.org.)

I repeat my appeal for any assistance in finding a PROPER replacement for the output transformer in my U-45B. Thank you. Talk to ya....

Doc George

[BobB]

I used the Hammond 125-h and this schematic.
The amp sounds great.
Univox copied a Gibson GA8-T for the U45-b


Bob

[mykey]

I used the Hammond 125-h and this schematic.
The amp sounds great.
Univox copied a Gibson GA8-T for the U45-b


Bob

the schematic I'm looking at here says 5K primary, 8 ohm secondary, however I cannot attest to the authenticity or accuracy of the schematic. The Hammond tranny will no doubt work just fine. It is regrettable that there are no longer exact replacement parts, but I have seen these amps being sold used for $125.
The UB-45 is an exact clone of the Gibson amp, but the transformers were probably not made in USA. The old tranny could be rewound by Peter Dahl or similar shop, for a rather steep price compared to buying another used UB-45. Buying a working used UB-45 would provide the transformer blueprint to rewind the bad one, close as possible to the working stock one.
If I find anything else, I will forward that to you, good luck.

[Dave Curtis, dB AudioTech]

I picked up a U45b chassis from ebay a few months back and had the same problem. It turned out to be just a broken connection just under the paper; a bit of very tedious soldering fixed it. Be very careful with the connecting leads on it. The trannies in these things are very cheap. I'm sure the replacement Hammond mentioned would sound much better. BTW, mine is marked "P 16K P" on the primary and "8 ohm" on the secondary.

[DocGeorge]

Hi Dave:

THANKS for the info- it's just the sort of reply I was hoping for- perhaps someone else has a U-45B with a labelled OT and we can find out the manufacturer and model #....

Actually, when I inspected my transformer I noted the same thing- the wire had melted through where it's connected- HOWEVER, I figure that this happened for a reason, and that the melted wire had acted as a fuse. Rather than simply soldering the connection closed again, I figured I would check out the amp and bring it up to specs before putting in the CORRECT OT. (Perhaps I will give it a shot, though.)

I like that your OT is stamped 16K- I'm sure that that's correct, and that that value was chosen for a reason.

Anyway, have fun with yer U-45B- IF you haven't, you might like to look at Univox.org...talk to ya....

Doc George

[samwheat]

i had one of those amps ..... 6aq5 power tube in SE, 4w output ...... i rebuilt it cause the trem didn't work ...... pcb ....... sold it last year ....... i still have the schematic, it sounded great once rebuilt

it has a 5k/8ohm OT

i think they made these with 6bm8's in PP also

[Rob Mercure]

DocG

I'll have to agree with most of the other respondents that you'd probably be satisfied with more commonly available trannies but with that stated if you'd provide all numbers stamped on your tranny I may have something same/similar in the attic - but I'm not going to go rummaging up there unless I've got everything you can provide first.

Secondly, breaks in OT primary windings, especially where the larger insulated plate and B+ leads connect to the much finer enameled wires are quite common. This is after all the weakest mechanical link and I've accidentally broken such by simply grabbing after a tranny that was about to fall off the work bench and caught the lead instead of having a solid grasp on the core. As such repairing the break is quite feasible but, as noted, quite "tedious" - it requires good soldering technique coupled with some experience. Over the years I guess I've averaged about a "50/50" success rate in restoring open circuits when I decided to cut into the paper and the rate would be higher but there are times the break is deep inside the windings or the unit was so overheated that the enamel insulation is baked and flakey and even a good soldering job would still only complete the connections to a shorted tranny.

So, tell ya what, if you'd like someone with some experience to take a shot at it I would be willing to do so and only charge you if successful - although I would expect you to pay shipping both ways no matter what. If you're interested PM me and we'll talk about details.

Rob