#1
I have a Marshall AVT20 Hybrid Tube amp that I acquired last month from Craigslist. I tried out the OD channel a little when I sampled the amp but I mostly play clean stuff so I didn't really notice this, but now, when I turn up the amp even slightly, we're talking not even close to gig volume the amp squeals horribly. My gain is at 12, volume way down at 7-8oclock, and I don't even have a distortion pedal plugged in. I just bought a Boss NS-2 noise gate hoping this would fix the issue and it hardly touched it so I'm starting to think there is something faulty in the amp. Brand new guitar, has this issue across multiple guitars and cables so it must be the amp. Any thoughts on what I can do? I've already purchased a new preamp tube.
#2
If you already replaced the preamp tube then I'm clueless.

Did you replace the preamp tube when this problem started of for a different reason? Which preamp tube exactly?

What does it sound like with the preamp tube removed?

Does it have a footswitch or a footswitch jack for clean/dirt? Sometime those can get borked.

Is the squealing constant or does is vary based on different things (turning dials in different directions, different room, gain level, pedals, etc)
#3
Tube is in the mail, its a 12ax7 tube i believe. i havent opened the back but i believe its only a single preamp tube in there. no footswitch for clean/dirty. somebody mentioned it could have something to do with a faulty reverb function. problem is only made worse when i turn on the CS3 compressor. lots more noise, and almost instant feedback.
Last edited by jeremiah.roth54 at May 13, 2015,
#4
Replace the tube and then get back to us. And yes, one 12AX7. It's only engaged on the drive channel IIRC.
Gilchrist custom
Yamaha SBG500
Telecasters
Randall RM100 & RM20
Marshall JTM45 clone
Marshall JCM900 4102 (modded)
Marshall 18W clone
Fender 5F1 Champ clone
Atomic Amplifire
Marshall 1960A
Boss GT-100


Cathbard Amplification
My band
#5
Now, I am sitting quite close to my amp, I know this is bad, but I am not playing at high volume at all, volume is at about 20% and the gain is at 50%, in my experience being too close like I am in a major no no at high volume and gain, but I am doing neither of these. Granted, it probably doesnt help, but i think there is something else going on here.
#6
I think squealing from broken reverb paths is fairly common. So yeah, get the squeal happening and see if messing with the reverb does anything. Do that with other knobs as well. Let us know if the new preamp tube helps.
#8
You can't tell like that. Just replace it and see.
Gilchrist custom
Yamaha SBG500
Telecasters
Randall RM100 & RM20
Marshall JTM45 clone
Marshall JCM900 4102 (modded)
Marshall 18W clone
Fender 5F1 Champ clone
Atomic Amplifire
Marshall 1960A
Boss GT-100


Cathbard Amplification
My band
#10
Microphonic pickup.

http://www.guitarnuts.com/technical/electrical/index.php

I use regular canning wax available at grocery stores, Gulfwax is the usual brand. I picked up a potpourri pot at a resale shop for a buck, similar to a mini crock pot, it works great. Produces enough heat to melt the wax but not enough to set it on fire or brown it. Just let it heat till it's melted and drop the pickup in, let it stay till it stops releasing air bubbles. Use something like alligator clip to hang the wires above the pot. Clean off all wax on the top where it's visible installed, it's a bit hot but can be done with a paper towel soon as it's pulled out of the pot. Leave the underside alone especially where the tape is around the windings, do not remove that tape.
Hmmm...I wonder what this button does...
#11
Quote by Paleo Pete
Microphonic pickup.

http://www.guitarnuts.com/technical/electrical/index.php

I use regular canning wax available at grocery stores, Gulfwax is the usual brand. I picked up a potpourri pot at a resale shop for a buck, similar to a mini crock pot, it works great. Produces enough heat to melt the wax but not enough to set it on fire or brown it. Just let it heat till it's melted and drop the pickup in, let it stay till it stops releasing air bubbles. Use something like alligator clip to hang the wires above the pot. Clean off all wax on the top where it's visible installed, it's a bit hot but can be done with a paper towel soon as it's pulled out of the pot. Leave the underside alone especially where the tape is around the windings, do not remove that tape.

Quote by jeremiah.roth54
Brand new guitar, has this issue across multiple guitars and cables so it must be the amp.
#12
Good call, I missed the multiple guitars part. Otherwise, sounded a lot like microphonic pickup, which is not uncommon.
Hmmm...I wonder what this button does...
#13
How close do you have to stand and playing how loud before it starts to squeal?
Gilchrist custom
Yamaha SBG500
Telecasters
Randall RM100 & RM20
Marshall JTM45 clone
Marshall JCM900 4102 (modded)
Marshall 18W clone
Fender 5F1 Champ clone
Atomic Amplifire
Marshall 1960A
Boss GT-100


Cathbard Amplification
My band