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Let's Get Technical => Power Amp Tech => Topic started by: Dante on April 24, 2024, 12:09:08 PM

Title: MT100 Output Transistor Issues
Post by: Dante on April 24, 2024, 12:09:08 PM

@Harley
I will start another thread after this...check out the pix below. One question, where does that yellow wire belong? It's not connected to anything and it looks like it was pulled off something, but I don't see anything loose  :dunno:

Dante

Title: MT100 Output Transistor Issues
Post by: Harley Hexxe on April 24, 2024, 02:59:47 PM

Dante,

    Okay, I had to dig out one of my MT 100s to find out. That yellow wire isn't connected to anything. It should be folded back, and zip tied  to the bundle of red wires. That's what I see in mine.

    Yes, those two things under that clamp are the power transistors I believe. They have a mylar sheet under the back of the head. Be sure that is in place when you install the new ones.

     They are: IRF9530 and IRF530 going from left to right

Title: MT100 Output Transistor Issues
Post by: Dante on April 24, 2024, 03:37:39 PM

Thanks Harley!!

I found a low resolution pic of somebody repairing one, it was folded back and bundled with a zip tie. I couldn't figure out what to connect it to, now I  know. I can also see the dent in my wires where the zip tie used to be.

I see those exact part numbers on mine, now that I've removed that bar from the top. Both are greasy on top, eeeewww...each of these thingys is on a pile of white grease (dialectric?) and there's a square sheet of something under each one, gotta be the mylar

I'll order 10 of each part, shipping will be more than the items :)
Here's the order....look right? (https://www.mouser.com/ProjectManager/ProjectDetail.aspx?AccessID=ab2b6966d9)

The real question is, how long with this thing last once I replace those? Am I doomed to do this repair over an over ?

Title: MT100 Output Transistor Issues
Post by: Harley Hexxe on April 25, 2024, 12:35:39 PM

Dante,

   The 1st one on the order looks right, but I'm not so sure about the second one. There is an extra digit there that concerns me IRF530(5).

   Is there only one brand to choose from? I might go with one that is a little more pricey if it means it will last longer. I haven't looked on the site for quite a few years, so I'll have to go check after typing this.

   I'm not sure it that goo is dielectric grease. I guess it could be, but all the dielectric grease I see these days is more milky looking. Does it smell like grease?

   As for your last question, I have no answer. All my MT100s failed on one channel even after repairs. That's why I posted the question decades ago about the cause. I was wondering if running it in bridged mode had something to do with it.

Title: MT100 Output Transistor Issues
Post by: Dante on April 25, 2024, 02:16:19 PM

Nice catch, I did not see that. I updated the order, Have a Look See (https://www.mouser.com/ProjectManager/ProjectDetail.aspx?AccessID=04ef14ba5a)

Title: Re: MT100 Output Transistor Issues
Post by: Harley Hexxe on April 26, 2024, 01:33:43 PM

Dante, that looks like it will do the job.

Vishay has a pretty good reputation for their caps with amp techs, hopefully, these follow that reputation.

I should really quit procrastinating and just order a pile of those and get busy with my MT100s. After all, I do like the sound of these better than the MT200s.

Title: Re: MT100 Output Transistor Issues
Post by: Dante on April 26, 2024, 05:24:17 PM

Thanks man, I appreciate you confirming that before I order. They are on the way, I'll do it 5 more times....after the 5th time, I sell it :)

just kidding

Title: Re: MT100 Output Transistor Issues
Post by: Harley Hexxe on April 28, 2024, 06:21:02 AM

I'm not sure if it will work in the MT100s, but I'll probably also order Sovtek 12AX7s to swap out the tubes in those too.

  I did notice in the MT200, when I swapped the original tubes with a pair of tubes that distorted earlier, that it warmed that amp up considerably.