Output Transformers

temperx2 · Post by **temperx2** » Sun Jul 25, 2004 4:21 pm

I have a reissue of an OD 120 that keeps on blowing output transformers. Has anyone else heard of this happening to these amps. It worked fine for 6 years and then the tubes were changed and it started blowing transformers. Any Ideas anyone cause this if frustrating and expensive.

User · Post by **User** » Sun Jul 25, 2004 4:33 pm

Blowing transformers??? (Hopefully im not being patronising here but...) You are talking about those big metal thinks with coils on them arenÃ¢â‚¬â„¢t you?
The thing on the right of this picture
<img src="http://users.pandora.be/geertjacobs/OFG ... SL3far.jpg" border=0>

Dave

Edited by - user on 25 Jul 2004 16:36:31

Post by **bclaire** » Sun Jul 25, 2004 4:57 pm

Yeah- output trannys are in the $200+ range so replacing them is way expensive. They don't go unless you're running the amp without speakers attached...

I hope that an amp tech is taking responsibility for the repairs as a transformer blowing after it has been replaced would be the tech's fault.

Please tell me you're not trying to do this yourself...

Billy

Post by **bclaire** » Sun Jul 25, 2004 4:59 pm

I just went to Mercury Magnetics website and output trannys are $250.

www.mercurymagnetics.com

spoonie g · Post by **spoonie g** » Mon Jul 26, 2004 3:11 am

From a few guys I've talked to, this seems to be a common problem with these amps for some reason. One guy I knew replaced two.

Andy H. · Post by **Andy H.** » Mon Jul 26, 2004 8:41 am

According to Five Eight and Ten writing elsewhere:
http://vintageamps.com/PlexiPalaceUBBcg ... 4;t=001015
...the '90's reissues didn't have as strong transformers and did sometimes blow them, especially if the speaker impedance was mis-matched.
I think Billy is right though - the tech should take responsibility for subsequent failures.
Oranges tend to hit the output side of things with higher voltages then for example Marshalls, so if they are used to thinking 'Marshall' specs, they need to think again!
Q. What sort of OT's have they been fitting?
Q. How long did they warranty the work for, and how long did it actually last?

fiveightandten · Post by **fiveightandten** » Fri Aug 06, 2004 2:00 am

<BLOCKQUOTE id=quote>quote:<hr height=1 noshade id=quote>
I have a reissue of an OD 120 that keeps on blowing output transformers. Has anyone else heard of this happening to these amps. It worked fine for 6 years and then the tubes were changed and it started blowing transformers. Any Ideas anyone cause this if frustrating and expensive.

<hr height=1 noshade id=quote></BLOCKQUOTE id=quote>

I have a friend who's 90's OR-120 was doing this. It blew 2 output trannys in a week.

-The original blew before he got the amp. Not sure why that happened. But the original owner was in a touring band, and more or less abandoned the head at a shop, saying they would contact the tech when they got home...and never did.

-The tech was able to find a NOS stock OT for a 90's reissue. Still in the box, never used. (This was a few years back). 3 years went by, and he never heard from the band. He decided to put the new OT in and sell the hed. He put the brand new Orange OT in, and sold it to my friend (via eBay). 2 days of normal use, and it blew that OT.

-Being a man of his word (and apparently a VERY nice guy), the tech agreed to pay for a brand new OT. My friend ordered a Mercury Magnetics iron, which the tech paid for in full (nice, huh;) ). And it's been fine ever since then.

At any rate...my friend's Dad is an electrical engineer, and a damn good amp tech. He had the head on the bench for 2 weeks before installing the new OT, trying to figure out what was wrong with it and why the heck it could be eating OT's like that. I brought my 90's 120 down and left it there as an example, so he could see if the voltages were on. The NOS 90's OT in my friend's head was still functional...but it was half toasted, and you could hear it crapping out at high volumes.

He noticed that the damaged head had a higher voltage drop across the screen grids than mine did. So he suspected that something was drawing more current than it should be. It wasn't clear however, if that was just a consequence of the OT being on the way out though. In the end he replaced it with the MM iron, and checked everything out thouroughly before playing it. All the voltages were the same as before, and that slightly higher voltage drop seemed to be normal to the amp. I don't think he ever figured out why all those OT's blew. And the MM unit has been in there for a few years with no problems at all.

I should mention that mine blew the stock OT 2 days after I got it. It was An OR-80 at the time though, and I don't know how it was treated before it came to me. I replaced it with an AD140 OT, and I haven't had any problems since.

If it were my amp, i'd recap the whole amp, and replace all the diodes in the bridge rectifier. Then you know your whole power section is brand new. It can't possibly blow a tranformer if all the parts are functioning properly...at least that's what one would think. It'll cost you less than $50 in parts.

That being said, this kind of thing is beyond my knowledge to understand, if it is a concrete problem that can be pinpointed. Ask around over at www.firebottle.com/ampage in the the amp forums...those guys are way more bad-ass than i'll ever be, and they just may be able to tell you what it is and how to prevent it.

Hope that helps.

-Nick

P.S. By the way...is it the same side of the OT that keeps burning out, or it is different each time? My buddy's OR120 burnt out the same side on both the trannys his toasted. His dad also didn't change any parts in the amp, not even the tubes, before installing the MM OT. And like I said, that one has been fine for years...

fiveightandten · Post by **fiveightandten** » Fri Aug 06, 2004 2:03 am

<BLOCKQUOTE id=quote>quote:<hr height=1 noshade id=quote>
I have a reissue of an OD 120 that keeps on blowing output transformers. Has anyone else heard of this happening to these amps. It worked fine for 6 years and then the tubes were changed and it started blowing transformers. Any Ideas anyone cause this if frustrating and expensive.

<hr height=1 noshade id=quote></BLOCKQUOTE id=quote>

Woah, woah...I just re-read your post a bit more carefully.

It was fine...

The tubes got changed...

Now it's blowing multiple transformers?

Change the tubes!

-Nick

Output Transformers

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