JMP 1h loss of volume and gain

[Dan77]

Hi all,
Having a bit of a problem with my jmp 1 watt head and need some help. It was working fine last night through a 1960A cab, i usually have it on the 0.1watt setting and that's pretty loud through the 4x12. But i turned it on this morning and the volume had reduced to virtually nothing. There is still volume there but really quiet almost nothing in the 0.1watt setting with everything on 10. If i turn in to 1watt with the boost on aswell it gets up to a similar volume to how it usually is in 0.1watt but not really any gain/crunch.
Checked the guitar and lead on another amp and to make sure they were not the problem and they seem fine.
Has anybody else had a similar problem or got an idea what could be the issue?

Thanks
Dan

[P A U L]

1st thing, check the tubes. Sounds like a preamp, if you lost gain & power. Try just wiggling the tubes while firmly pressing in on them. Or, you could just pull them out 1 at a time & reseat them firlmy & see if that does anything. If not, try swapping (w/ new, or known good) the pre-amp tube(s) & see what happens.

Could be a connection on the input or pre, but try the tubes 1st...

[Torshalla]

Really sounds like a tube issue... had similar problems with my JCM1C and all went away when I swapped tubes...
Good luck!

[Dan77]

Hi Paul, Torshalla, thanks for help. Looks like I shall be ordering some new tubes then.
Might as well get a whole new set, any recommendations ?

[Torshalla]

HI Dan,
Well I am not really a specialist and have not experimented much with tubes... however you should see several threads on this forum about tube switching with these amps...
For my part I left my JMP1 stock and I have GT ECC83s (Groove tech) tubes in pre-amp for my JCM1. I don't remember what I put in the power amp stage... I kept an ECC82 but not sure of the brand... may have been a JJ (sorry Surf... :)).
Hope this helps!

[Cousin Muely]

Here's some ideas. http://marshallroadhouse.com/viewtopic.php?f=60&t=13355

I had a tube go bad a few weeks ago in my JVM1. I had no sound. Found the bad one and replaced it. Good as new and even the slight Pop that had always been there when I turned it off was gone. It had probably been barely hanging in there from the start.

[GuitarBuilder]

Preamp tube.

[Dan77]

Just looked online, Watford valves has a valve kit for the jmp 1watt. Gonna pick one up to see if that fixes the problem.
To be fair I really have no idea about valves types, positions or the merits of swapping them.

[GuitarBuilder]

One last thing to check before buying new valves: a tube socket connection could be loose.