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I just purchased a Marshall JCM 800 combo amp. The model is 4210. This is the first or second year that they made the amp. The problem is that the amp has to be turned up to 8 to play with any volume. Very unlike any Marshall amp i've ever owned. I see that someone put a new cap in the C36 slot. Can this be a mod? Does anyone know where I can find a wiring diagram or have any idea what is wrong? Any help would be greatly appreciated. Thanks
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Re: Marshall Jcm 800 Question
Check out Dr. Tube's site for a schematic. There's a link to his site on my site FJA Mods I repair them if you can't find anyone near you.
Jerry
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Re: Marshall Jcm 800 Question
http://www.drtube.com/marshall.htm#JCM800
A direct link.
How are the tubes? They could be smoked.Comment
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Re: Marshall Jcm 800 Question
So, you crank it up and only when you hit 8-10 is when you get any volume? How much volume? It should be peelin paint off walls at that level but it should be instantly audible from as soon as you start turning the master pot if your pre is up.
Could be any number of things, cold solder joint loose, a bad tube. Sounds like you had the chassis out and you know some basics.Comment
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Re: Marshall Jcm 800 Question
the drtube schematic is for a newer model. I need the one for a 1981. It seems that they changed some things after the first 2 years. You can hear the volume get louder from 1 on up. It's just that you have to get around 8 to have a useable amount of volume. I took the amp apart and found that someone soldered a large cap in slot C36. This is the only non original part in the amp. I can't seem to find what originally went in the C36 slot. The newer schematic is completely different.Comment
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Re: Marshall Jcm 800 Question
Sounds like something is wrong. Id get it in for a checkup ASAP.Comment
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