Greetings! Need some help please

[Skizzers]

Greetings all!

I hope someone can help me with an Express 5:50 situation here...
My amp is running well and I love the all the tones I'm getting with my strat but I have a problem with the OD channel (Blues/Burn). Whenever my master volume hits around 12-1 o'clock positon I get a HUGE nasty sounding squeal from the speaker. This happens even with no guitar plugged in and only when in 50 watt mode. It does not happen in class A 5 watt mode. All other amp functions are fine. I'm guessing a bad tube somewhere and would appreciate any advice you folks could offer. (I will admit I'm a total "tube-newb" as this is my first tube amp.)

many thanks in advance

Skizzers

 

[EtherealWidow]

Sound like you're on the right track assuming it's the tubes. Probably a bad preamp tube somewhere, although I have no idea why it wouldn't do it in class A as well. Best advice is to grab a good preamp tube and swap them out one by one. Take it with a grain of salt though because this is just one self-professed noob talking to another. (Only my 2nd tube amp) Any second opinions?

 

[Skizzers]

Thanks for the reply EtherealWidow...

I just found that is does happen as well in Class A, I just cranked the master volume all the way and it started to squeal near max. I'll try to swap some pre-amp tubes.

Skizzers

 

[Uncle Rocker]

Sounds like a tube's gone microphonic to me. You might find it by tapping on each tube w/ the eraser end of a pencil until you find the one that makes noise when you hit it. You'll need to take the covers off the pre amp tubes first. But, it could also be a power tube so check them too.

 

[EtherealWidow]

When you knock on the first tube though, be aware that it will always probably make noise because it's the first in the tone stack.

 

[Skizzers]

Thanks for all the help everyone!

It turns out I had a bad preamp tube in V2 so I replaced it and all is well in "Boogieland" again.

Cheers!

Skizzers