UA 1108 transformers

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fazer

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I have a pair of 1108,s. They have input transformer IT 5000 and output trans 5002. In a UA article it says the 1176 uses the same input and output transformer. I thought the 1176 uses an O8 ouncer. Is the IT 5000 just a rectangular O8? It seems larger. Here is a pic with an O16 which is the same size as an O8
 

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mjrippe

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The 1176 uses an O-12. The O-16 is not the same size as other O series transformers. I don't know what article you are reading but it seems to be rubbish.
 

dmp

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The 1176 uses a line transformer (600:600)
The 1108 is a mic to grid. O-16 is 250:50k
The 1108 input is a custom from what I've read. There was quite a bit written about it here in the past if you search. Probably most similar to O-1, as that was what was in the tube predecessor ua 610
 

mjrippe

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The 1176 uses a line transformer (600:600)
The 1108 is a mic to grid. O-16 is 250:50k
The 1108 input is a custom from what I've read. There was quite a bit written about it here in the past if you search. Probably most similar to O-1, as that was what was in the tube predecessor ua 610
Please see the attached UTC catalog page for the O series.

1176 uses O-12 which is 50/250:50/250/500 There is no 600:600 option.

1108 is a transistor preamp, so there is no grid.

O-16 is 250:50k, correct. The O-1 and O-2 can also be wired for the same impedances, but the O-16 has permalloy shielding built in and does not fit or use the O-17 shield.

1108 is most likely custom, agreed.

The 610 did use the O-1.
 

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dmp

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I should have said the O-12 is 1:1. I don't think there is any difference between a 250:250 and 600:600 line transformer, but you are right, it was not marketed as 600:600.
The 1108 used what is usually referred to as a 'mic' transformer but does not have a grid, correct. I was following the "mike, pickup or line to grid" or "low impedance to grid" description from the UTC catalog for the O-1 and O-16, meaning it's a step up transformer.
I guess I shouldn't post unless I have the time to make sure all the details are right.

The 1108 and the 1008 both used the same input transformer. The 1108 used the same output transformer as the class 'A' 1176 which is the 5004. The 1008 used a 5946 which was the same output transformer used in the 175 tube compressor and the 610 mic channel. All of the transformers were custom made and are not UTC's or such. Hope that answers your questions.


Edit: I should clarify what I meant by "not UTC's or such". I mean that they were not an off the shelf UTC transformer. The input transformer for instance had a Universal Audio Internal part number of IT-5000. However, the transformer inside the can could have been made by Peerless, UTC, EE or Microtran. From the documents I've seen, all four brands were used at one time or another. It depended on who could supply them in a given time frame and at what price per quantity required.

OK, here's "some" info regarding the input transformer for the 1108, 1008 and 1016. Enough to get you close anyway.

Spec calls for:

Primary Z of 600, 150 and 37.5 ohms.
Primary being Bifilar wound.
Secondary Z of 65K +/- 2K although the Peerless version measured 70K - shock!!!!
Core may be EI-375 HYMU .014 3/8" stk or equiv.

Various manufacturers used and the internal part numbers:

Microtran: Micro W5127
Also Microtran M1-A
Peerless: 4786
UTC: 6448
EE (Electro Engineering Works): EE4786-E14650

I have windings DCR of the UTC, the Peerless and the EE but not the Microtrans. Not much between them but the Peerless measures higher on all windings.

A UTC 0-1 was also considered and tested but not used.


I do have the full info for the 1008, 175 output (the 5946). It was made by UTC and, contrary to what I had remembered, also by Electro Engineering Works.

I need to keep this info to myself for the time being. I may need it down the line.

Still, you have a bit more to be getting on with now I suppose.

W.
 

mjrippe

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I was not trying to pick on you dmp, it was just that the OP had so much misinformation already that I wanted to post solid facts. Thank you for taking the time to dig up those other threads!
 
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I should have said the O-12 is 1:1. I don't think there is any difference between a 250:250 and 600:600 line transformer, but you are right, it was not marketed as 600:600.
The difference between accurately spec’d 1:1 transformers at differently rated impedance is reflected primarily in low frequency response, where the higher the rated inductance = better low frequency response pole. So a 250:250 won’t reach as low as a 600:600 all other things equal. Note that it could be the difference between 3Hz and 1.5Hz or 100Hz vs 50Hz depending on source impedance.
 

dmp

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Wow, you're right - I forgot that it isn't wired 1:1. Connection is input to 1,5 and output from 6,8 so it is 500:200 or a step down ratio of 1.58
 

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