Marshall sqeal at high gains...wtf?

[hareek]

Re: Marshall sqeal at high gains...wtf?

9-pin tubes can't be rotated wrong in their sockets unless you REALLY force something.

Make sure all the tubes are firmly seated in their sockets. Turn up until it squeals. Does it do it with the guitar turned all the way down? If no, then it might be the guitar.

If yes, look to a microphonic tube. Just tap each preamp tube lightly with a pencil or something else non-metallic. The microphonic tube will make a ringing noise, noticeably louder than the others.

yeah it makes the noise with the guitar turned down and when I turn the lead channel up to about 4 with the gain cranked all the way. It stops when I back off the level on the channel. I'm about to do the "tapping" method right now and see what happens. I"ll post my results shortly. Thanks.

 

[Rich_S]

Re: Marshall sqeal at high gains...wtf?

Do your tapping with the volume and/or gain just below where the squeal occurs. It should be pretty obvious.

And next time you get Chinese take-out, save a pair of wooden chopsticks. That's the tech-approved tool for poking around tube amps.

 

[hareek]

Re: Marshall sqeal at high gains...wtf?

ok there's the three pre-amp tubes and the one with the metal casing over it. the far right tube made a small ringing noise. the next one over made a small ringing noise. the third one made a ringing noise slightly louder than the other two but it wasn't dramatically louder. thoughts?

edit: actually now its hard to tell the difference between them. maybe more than one tube is bad

 

[hareek]

Re: Marshall sqeal at high gains...wtf?

I don't know if its a tube or not anymore. I just tapped the end of my guitar cord that's on the input end at the amplifier and it made the most horrific noise ever. Back when the amp was making a bad hum, marshall diagnosed it as something wrong behind the input and tech in Richmond, VA did something to fix it. It seemed like the hum was gone but now im having this feedback problem and the amp made a nasty noise when I hit the plug. I guess that could be normal as it has happened on other amps. It's just funny that it is in the spot where work has been done before. I might change out all the pre-amp tubes just be safe.