SMF help

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SMF help

Postby beerrhino on Fri Sep 19, 2014 5:33 pm

I have an SMF head that blew a power transformer about 6 months ago. The tech took it out and sent it to Mercury Magnetics and they cloned it. It worked fine for the next 6 months and then blew the power transformer again. It was sent back to mercury and they said it was a "slow burn" and not really their fault but replaced it under warranty anyway.
When the replacement was installed the tech told me that the secondary on the pt was regularly getting 1 amp of current and was rated at about 500ma, it was probably going to burn out again in about another 6 months. There are no faults or problems in the circuit, everything matches the schematic. They are talking about adding a big resistor before the secondary to knock the current down to a safe level, does anybody have any experience with this?
What I would like to know is is this a problem inherent to this model? They weren't made for very long, could this be why? Any other insight into this problem would be appreciated.
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Re: SMF help

Postby partsstan on Fri Sep 19, 2014 11:46 pm

I have not heard of this problem, but see if this helps your tech. http://soundcitysite.com/schems.shtml
There are SMF schematics with some voltage specs here. DMI who made these amps went out of business shortly after these were made. Good luck, please keep us posted. Stan :D :D :D
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Re: SMF help

Postby Papa Dog on Sat Sep 20, 2014 1:39 am

I would wonder if the transformer which you had rewound was original to that amp.
If it is indeed the correct transformer for that amp then there is another major issue.
Could be something simple like a bad or marginal tube, but whatever it is it is not a dead short to ground.

Which model SMF is it? Pics would help, especially gut shots.
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Re: SMF help

Postby beerrhino on Sat Sep 20, 2014 5:50 pm

It's not a bad tube, those have been checked. The first transformer that died was the original partridge transformer. The second one was a clone of the first made by Mercury Magnetics, I have to assume that they copied it exactly but I have no way to check. The techs tell me that there are no other problems with the amp, they've done a lot of good work for me so I trust their opinion. Under playing conditions though the secondary of the pt gets a constant 500ma, and frequently sees 1 amp.
I don't have a pic of the insides, it's still in the shop so I can't take one. This is the only pic I have of the ampImage
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Re: SMF help

Postby Papa Dog on Sat Sep 20, 2014 7:34 pm

is that a Sunn 4x15?
kewl kab

Anyway...by the time that SMFs were being done most Sound CIty (DMI) units had ElectroVoice transformers.
I would be surprised to learn that a Partridge was original to the unit. But, I have been worng before.

Seems like that amp must have some issue, either the wrong PT or some other issue causing it to draw excessive current. When you get the chance I would really like some good clear pics of the innerds to post on the Sound City site.
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Of cabbages--and kings--"
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Re: SMF help

Postby beerrhino on Sat Sep 20, 2014 8:18 pm

Thanks papa. I mentioned the electro voice transformer to the tech and he's looking into it. Hopefully it'll get working again.
And yes, that's a sunn 415M cab
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Re: SMF help

Postby beerrhino on Fri Sep 26, 2014 12:08 am

Here's a few pics of the inside:
ImageImage
Image
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Re: SMF help

Postby beerrhino on Fri Sep 26, 2014 12:10 am

2 more:
ImageImage
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