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I changed my 18 watt TMB channel (built with the old layout) over to the New Plexi circuit and while I am loving the sound it's caused a couple issues. First problem I noticed is that with the gain above maybe 1.5/2 if I touch the end of a cable plugged into the input I get a pretty loud squeal as opposed to the normal lower pitched buzz sound. Really have no idea what this could be.

Second problem is for about a minute or 2 after I turn the amp on the TMB channel sounds like crap then "fills out" and sounds great. By crap I mean that it sounds almost like a bad Fuzz Face with the gain pretty low. Sort of gaited and kind of clean with an unpleasant distortion in the background. But then it just goes away and sounds pretty great. I think all my solder joints look good and test alright with the multimeter and the wiring looks correct. Also tried a few different tubes in all the spots and that didn't make any difference. I tried searching the forum but didn't find anything dealing with this. Thanks for any ideas.

Well the crappy sound was from the shielded cable between the gain pot and v2. Replaced it and now it sounds great right away. More inspection and it seems the squeal is an occilation that I get with the vol and gain knobs high enough. Back to work!

Did you also change the vol pot from 1M to 500K and make any mods to the grid stopper on V2 as well.

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Usually caused by lead dress. Shorten wires, use coax cable; tubes can cause it too. More leads to tubes around to see if squeal stops.

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Hey thanks for the tips. I had some stuff come up then had to leave town for some shows so I haven't been able to get back to the amp. I found that list of thing to do to the 18 tmb side in one of the other subforums and have tried them all except for switching the output transformer taps because the amp doesn't squeal when I dime the Normal channel. I've got shielded cable everywhere I should and they are as short as they can be and up above the board. I've got the 68k/1m divider right on the tube socket of v2. I've tried several different tubes and the problem persists. I've also chopsticked all around the amp and have, i believe at least, followed proper lead dress (plates away from grids, only cross wires at 90 degrees, all that stuff) I'm not sure if I have a 500k or 1m gain pot. I'll check the next chance I get. I feel like it could be a 1m cause this thing has quite a bit of gain for 2 gain stages!

Consequently this thing sounds great and only really squeals when it's turned up louder than I'd really use in a band context. I've been loving the thing with a Zvex Sho in front of it and am gonna use it at my next show In NY city this weekend with my 1x12 with a greenback. If anybody youtubes any of our set I'll post a link here.

Thanks for the help.

If it didn't squeal before, then you probably don't need to switch OT leads. But check the colours are per the layout.
Please post video!

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps