Jcm 800 volume drops and comes back up.

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ESPzach

New member
I was recently offered a 1987 jcm 800
50w 2 channel by a friend for a very reasonable price but it has a small issue as he described...

It's got a little bit of an issue, may not be a big deal if you know an amp guy but I'd give a good deal on it cause of it, after you play for awhile eventually the volume starts to go up and down, I think it's a bad Jack for the foot switch cause wiggle it and it sometimes fixes it , maybe a simple fix maybe a symptom of a bigger problem I don't know.

Any info helps! Thanks
 
Re: Jcm 800 volume drops and comes back up.

One way to check if it's the foot switch would be to play through it awhile without the foot switch plugged in. May be a pain switch channels manually on front of amp but would be worth a try. Also could be tubes . They will still light up and even work to some degree when they are dying but will often cause volume
Drops like that cause they can no longer push the power as they should.
 
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Re: Jcm 800 volume drops and comes back up.

Try it with nothing but the guitar (and cab, duh!) plugged in. Does it do this?

There are two main reasons I have seen this happen:

-Tubes
-Dust in FX Loop or Footswitch jack causing it to short out.

you can also try just jumping the FX loop and see if it keeps doing it as well.
 
Re: Jcm 800 volume drops and comes back up.

loversmoon said:
One way to check if it's the foot switch would be to play through it awhile without the foot switch plugged in. May be a pain switch channels manually on front of amp but would be worth a try. Also could be tubes . They will still light up and even work to some degree when they are dying but will often cause volume
Drops like that cause they can no longer push the power as they should.
Click to expand...

The dual channel JCM800s can only use the dirty channel with no foot switch plugged in.

The OP's issue could also be caused by dirty tube sockets. My Jubilee was doing this a couple months ago as I'd had it in storage and hadn't powered it on for over a year. Pulling and re-seating V1 fixed the problem for me.
 
Re: Jcm 800 volume drops and comes back up.

I'll have to try those suggestions thanks a lot.I can get it for about $400 less than I see them going for and was gonna try to fix it and flip it.Marshall just isn't my thing lol
 
Re: Jcm 800 volume drops and comes back up.

My 2210 used to do that. Was an issue with the fx loop.
 
Re: Jcm 800 volume drops and comes back up.

I think if you can get it for a good price get it, its most likely an easy fix.

If your buying it just to flip, then don't, let someone else who actually wants one get it. I know a 'flipper' in my area and I ****ing hate him. Just jacks up the price and then puts a good guitar out of some kids reach.
 
Re: Jcm 800 volume drops and comes back up.

That kind of issue is often a faulty tube, tube socket or volume pot.

My Deluxe Reverb was doing that a couple of months ago and Bruce (Mission Amps/Denver) fixed it by replacing the volume control and a 12ax7 tube.
 
Re: Jcm 800 volume drops and comes back up.

I agree most likely a tube issue and most likely a preamp tube versus a power tube. Preamp tubes would be easy to swap and see if it fixes it. If a power tube which is less likely you have to know what you are doing if you swap any of them out as a BIAS is also required to properly change one of those.
 
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