Problems with guitar amp

[uriel]

I have a Peavey Classic 30 that I haven't touched for about 18 months or so, maybe longer. Last time I played it all was well.

A couple of days ago I turned it on and it's not right. With a guitar connected and the guitar's volume and tone both set to zero and the amp's reverb, bass, middle and treble set to zero, it's dead quiet. If you start to turn up the volume on the guitar it starts to hum like crazy, then as the guitar's volume is near full, it starts to quieten down again and once the guitar is full volume it's quiet, though not as quiet as when it's right down. If you turn the tone up on the guitar the noise gets terrible. And if the bass/middle/treble on the amp are up it gets worse again. It sounds as though you've got the amp really loud and the guitar is sitting right in front of the amp getting feedback.

While all this noise is going on, you can play the guitar and it sounds exactly as it should, at normal, quiet volumes underneath all the noise.

I was wondering wether it could be one or more valves on the way out? It uses 12AX7 pre-amp valves and I just happen to have a hi-fi amp that uses one and has a spare. I tried replacing each of the amp's pre-amp valves in turn with my spare, but it made no difference.

Does this sound like valves or something else? The amp, although being 4 or 5 years old probably only has a couple of hours use so I've never had any experience of the vavles expiring.

[GetCarter]

If the hum is the note 'G' then it's probably an earthing problem. Otherwise I think you could well be right re the valves.

[uriel]

I've just checked and the buzz seems to be half way between D# and E, at least to my tin ears. Guess it's time to start looking for a local repair/service place.

[paulmurr]

I've had similar problems with my JCM800, it had blown a number of power valves. You really don't want to be mucking about inside a valve amp unless you know what you're doing. A service + new valves at a dealer should be less than £100.

[chevy-stu]

probably power valves......

buy a new matched pair form someone like Here:
http://www.watfordvalves.com/includes/additem.asp?... (select matched pair in quantity)

They don't ned biasing, so you can just do it yourslef in about 15 minutes. For the £30 or so it'd cost I'd go for new power valves..


(early Peavey classics apparently has issues with the cheap valves & power supplies for europe being wrongly rated, and the often failed... 5 year old one's probably better)