pre amp valve ?

[bassmachine2112]

hi,i have a marshall mb450.it has a valve in the pre amp.the problem i,m havin is when you stop playing the rig goes into bass feedback which is like low mids howling.the only way to stop this is to damp the strings.the overall sound is very low mid to the point of booming.i have used different basses and it remains the same.i have used these basses on other amps and there is no problems so i think i can rule out the basses.could this be the pre amp valve/tube on the way out?

[dub]

It could well be the valve going microphonic, which happens when they are old, hopefully changing the valve could sort out the feedback. JJ Tesla vales are one of the best quality replacements.

[quote name='bassmachine2112' post='283063' date='Sep 13 2008, 09:24 AM']hi,i have a marshall mb450.it has a valve in the pre amp.the problem i,m havin is when you stop playing the rig goes into bass feedback which is like low mids howling.the only way to stop this is to damp the strings.the overall sound is very low mid to the point of booming.i have used different basses and it remains the same.i have used these basses on other amps and there is no problems so i think i can rule out the basses.could this be the pre amp valve/tube on the way out?[/quote]

Edited September 13, 2008 by dub

[bassmachine2112]

[quote name='dub' post='283088' date='Sep 13 2008, 10:44 AM']It could well be the valve going microphonic, which happens when they are old, hopefully changing the valve could sort out the feedback. JJ Tesla vales are one of the best quality replacements.[/quote]

well thanks for the replies,turned out it was a cracked preamp valve n all is good now.finally hearing what a crackin amp this is.thanks for the help

[orangepeelneil]

[size=3]Hi There,

How do you find the MB450 generally?.
I have the marshalll 4x10" cab that matches the head and wondering how it sounds?

Being a newer amp there are minimal reviews.

Regards,

Neil [/size]