Need help finding JMP-1 transformer

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jamminpete
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Post by jamminpete »

Hello

Anyone have a source for a transformer for a JMP-1 preamp?
I may have to rebuild if I cannot find. In case I need to rebuild, anyone know what the HT voltage is supposed to be? Based on schematic the LT secondary appears to be 12V then there is a 15V center tapped also but it doesn't say what the HT secondary voltage is.

Any info would be appreciated.

Thanks
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transformer wiring

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soulsonic
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Post by soulsonic »

You could try contacting the manufacturer and ask them about it.
http://www.dagnall.co.uk/about/contact.html
It's a model TXMA-00014...

EDIT: elsewhere on their website they say they specifically don't sell spares for Marshall products and to contact Marshall about it, but perhaps they'd still be willing to at least share the specs with you.
Marshall's website now says they don't sell any spares to "the general public".
"Analog electronics in music is dead. Analog effects pedal design is a dead art." - Fran

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Jmpj48
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Jmpj48
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Post by Jmpj48 »

There transformers are kinda expensive. But they are top notch I had to replace my transformer in my ada mp1 got it from mercury magnetics.This is the only place I have found that makes there on transformers.

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jamminpete
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Post by jamminpete »

Thanks. I'm going to try to rewind it. The LT side is still good.

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Groovenut
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Post by Groovenut »

Given that the caps in the HT power supply are rated at 350V, I would guess they are running the filtered DC to the plate resistors at around 300 volts. Most Marshall preamps run this voltage between 245 and 350 volts, so it seems in the ball park.

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Post by okgb »

It seems a problem with those preamps that the transformers emit a fairly loud " acoustical " hum when they on, so you could do better!

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jamminpete
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Post by jamminpete »

I bought a new old stock from The Guitar Store on Reverb. He had one more for sale last time i checked in case anyone wants one. From the Netherlands and arrived in US within 4 days.

In case anyone wants to know the HT voltage is about 220VAC. When the amp is loaded down it drops to about 205VAC.
Its still not fixed though I am having other issues the -15V regulator is only outputting = -2V and there is nothing on the display.
Does not pass a signal either. Tubes have been tested good.

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jamminpete
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Post by jamminpete »

Replaced the 7915 regulator and everything powered on correctly. Then I was getting screeching noises on all the patches.
Did a factory reset: (Hold OD1+Clean1 then power the unit) and now it all works properly.

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