[jdsmodulus]

I have a Mesa Boogie Mark 4 rackmount head. It is from around 1994. It sounded great for many years and has never acted up but last night and many nights before recently after I play it, it screams out crazy noise out of the blue. I can push it for about 10-15 min then all of a sudden bam and it is really loud even though the amp is not. The tubes are all glowing and seem to be fine. It will do this even in standby mode? Any thoughts? Thanks

[strumminsix]

I'd reckon it's a tube. I seem to recall a similar problem and brought it to tech and said it was arching?!

Watch the tubes and try to make it happen!

[strumminsix]

I'd reckon it's a tube. I seem to recall a similar problem and brought it to tech and said it was arching?!

Watch the tubes and try to make it happen!

[Emoto]

First thing to do is always replace the tubes. Rare for it to be anything else.

[tigerstrat]

best guess is power tubes failing. you didn't say how long this quad has been in the amp.

[jdsmodulus]

Im embarrassed to say that I have never changed the tubes. Is there any tubes out there that are better that I should add? There is a few tube threads out there I just haven't read them!

[jeffm725]

Be careful,
It really isnt about whether or not you read some tube threads on rukind. Its more about knowing what specific ubes need to go into your Boogie. Mark 4's (and there can always be exceptions......... but..) are "self biasing" they do not have a bias pot or adjustment. This creates the need for a very specific tube tolerance. You will need to either call Mesa, or a reputable tube dealer who is experienced in dealing with Mesa Mark 4's.