Bias spiked outta nowhere

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gadgetfreak
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Bias spiked outta nowhere

Post by gadgetfreak » Thu Sep 28, 2017 8:28 pm

So I'm jamming on about volume 4 gain@ 6 and master @4 and out of nowhere my amp kind of made a little pop not even really a pop but something like that. Next thing I know my volume wasn't that loud and I thought i blew a tube. Weird thing is I changed the PI and seemed to sound thicker again but I noticed over the next couple of weeks something wasn't right.

i just cracked her open and checked my bias, one tube was 36mv and the other was Ready for it, almost 60mv. How did that not fry something? Is that something power tubes can do. I just rebias'd and she's holding steady at 38mv for 460 pv and all sound's amazing and back to what I know to be my amp.

Just curious if that is something I should look into further or if it aint broke don't fix it? Btw Im using JJ kt77's, I'm ready to buy some new tubes just to try el34's again but these Kt77s are only about a yr old and not an insane amount of use. What are ya'll thoughts on a tube drifting that far without redplating? Pretty crazy and a test to how stout JJ's are whether you like em or not and I'm not affliated at all. The amp came used with them already in it.

One more interesting thing that may lead a real amp tech to something is I sprung for some NOS SED Winged C's and they were the real deal and one of them went up in a fire works show inside the tube and I believe it was the same tube that was at about 60mA and yes I definitley rebias'd between changes. so now I have 1 amazing NOS Sed Winged C with about 10 hours on it and can't find a match anywhere. Ok don't want to sidetrack my own thread but thought that may clue an amp tech to something bigger going on. Thanks guys/gals if your out there
2016 Goodsell Super17 MKlV in Tweed
2013 Marshall Jvm 205Head
2002 Rivera Quiana 30/15
2012 Fishman Loudbox mini
2015 Avatar Vintage 212 W/ 20W Heritage Greenbacks


2016 Gibson Les Paul Standard Heritage Cherry burst
2000 Fender strat Texas Specials&wiring,other mods
1998 Epiphone Les Paul plus top 57 classics/+ & 50's wiring,Bone nut, other mods
1989 Squire Usa model Rumpelstiltskin&wiring,other mods
1977 Greco Sa-900
2016 Martin HD-28
1979 Guild D-35
1984 Sigma Martin D-35

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