philipeby

I have a jcm 900 duel reverb that has a broken volume pot. anyone know how to replace them! seems pretty straight forword but I wanted to make sure I don't break it. Also, any advice on mods for this amp! I've had it for 2 years or so and never done anything but retube it. Thanks!

Philip

Marshall Amps

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00jett

i messed with the bright cap and the tone slope resistor on my old 900, it helped the fatten up the sound a bit a tamed the highs a bit. this mod with a good set of tubes (e34l's) really can make some nice tones come out of these things.

philipeby

I'm really new to this! Is that pretty easy to do! Is there a place I can find instructions?

thanks!

00jett

hey i tried some of the mods at this link.
http://web.aoct.org/marshall/jcm900-gain-mod.txt
however despite the good reviews about these mods i found i didn't like it myself. its supposed to boost the mids and lows and cut some treble and also add gain. i thought this amp already had an immense amount of gain and this mod added more. too much IMO. What worked for me was looking at this mod to figure out the schematics a bit and then i kinda formulated my own mod from there. there is a free download you can get by searching google called 'Tone Stack Calculator' this shows your eq curve and shows on a display what changing cap, resistor, and pot values will do. i found it really helped my 900. although in the end i traded it for a dsl 50 head not because i didn't like it, i just wanted to go the head and cab route instead of carrying around the combo i had. hope this might spark some help. with a little help these amps rock i think. wouldn't mind having the head version someday. oh and a good set of tubes and speakers will work wonders.