Amp Problem - Volume Fluctuating

[Speiro]

Hi all, I have a Marshall JMP-1 running into a Peavey Classic 50/50 with a Rocktron Xpression linked to the Marshall. Last night I noticed the volume going up and down when we were practicing. A couple of weeks ago when I was loading th rack case into my car I knocked it over (it was upright at floor level when it fell over). Could this be a valve issue or maybe dry joints causing the problem when the amp is getting warm? I have a gig this Saturday that we are getting paid well for and I don't want to screw the gig up.
Thanks for any advice on this.

[roodyrocker]

Hi all, I have a Marshall JMP-1 running into a Peavey Classic 50/50 with a Rocktron Xpression linked to the Marshall. Last night I noticed the volume going up and down when we were practicing. A couple of weeks ago when I was loading th rack case into my car I knocked it over (it was upright at floor level when it fell over). Could this be a valve issue or maybe dry joints causing the problem when the amp is getting warm? I have a gig this Saturday that we are getting paid well for and I don't want to screw the gig up.
Thanks for any advice on this.

I've had a problem with volume as well as gain fluctuating up and down only at one club we played at. This was with my Bogner Uberschall which I bought new and is well taken care of. If has never done this anywhere else except that particular club, twice! I talked to Furman about it and after a lengthy discussion we figured it was the crappy wiring/grid in our area. Have you tried running yours through a good power conditioner?
The only other time I ran into this volume drop is during the summer time when the club's A/C kicks on. In that club my Mesa Dual Recto as well as a friend's Dual Recto responded with not having enough guts to them. Switched to a different outlet not on the same circuit and problem solved.
Oh, during practice once I lost all volume on my Dual Recto and that turned out to be a bad capacitor. Had to be replaced by a tech and all is well again.

[JACKSONFREAK]

Sounds like an output tube may have gotten jared and may be leaking. causing the volume fluctuation. It could also be a cracked tube socket. Try swapping the tubes out first. If it still does it then you have other issues. Just remeber if you dont have soimething like groove tubes in the amp then you will have to get it biased.
Gil

[Speiro]

Thanks guys. I had it on all afternoon at home yesterday afternoon so it got nice and warm and it wasn't doing it. Fingers crossed it's OK for the gig this Saturday.

[roodyrocker]

Thanks guys. I had it on all afternoon at home yesterday afternoon so it got nice and warm and it wasn't doing it. Fingers crossed it's OK for the gig this Saturday.

Was it doing it at another place, like practice? If so, and its fine elsewhere then you may have run into the same thing I did with crappy voltage at that particular location or an A/C unit that kicked on while the amp was on the same circuit.

[Spivonious]

My amp does that sometimes but only at home and only when running in Triode mode; Pentode mode works fine.

[OnlineStageGear]

I have had tubes get loose in the sockets and cuase the same kinda volume drops. When that happens, you can pull the tube most of the way out so the legs are just barely in the holes and give the tube a twist so the legs now have a bit of an angle on them so when they go back in the socket, they sit more snug. That only works if the tab on the middle shaft isn't all the way down the shaft. If it is, you can just pull the tube out and slightly bend the legs. Just be careful you don't bend the legs too much.

A volume pot starting to get scratchy can cause the same thing and well as an effects loop loosing it's connectivity on the plugs.

[Speiro]

Roody, yes it was at a different place and I have since discovered that the roof where we practice had a massive leak the night before we were in so there could have been issues from that.
Online - I did notice a very scratchy volume pot o the amp and thought nothing of it at the time and I did give it a good tweaking before I tried it at home so maybe it was that. I'll have to get the contact cleaner on it.

[demeyes]

I've had a similar problem with my Laney GH50L head. I've retubed it now but I haven't given it a good run to see if it's fixed now or not.

[roodyrocker]

Roody, yes it was at a different place and I have since discovered that the roof where we practice had a massive leak the night before we were in so there could have been issues from that.
Online - I did notice a very scratchy volume pot o the amp and thought nothing of it at the time and I did give it a good tweaking before I tried it at home so maybe it was that. I'll have to get the contact cleaner on it.

Did water get in your amp? or was the leak in another area of the room (hopefully)?