Possible Bias issue?? - diyAudio
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Old 6th November 2012, 05:57 AM   #1
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Default Possible Bias issue??

Ok amp is Crate stealth 50 etc 4 6v6, 312ax7 PP I now have the 2 outer tubes pulled so running on the inner 2(JJ6v6) Now it has 420v on plates and about 410 on screens now it has adjustable Negative grid voltage the range to set it is between -37 and -34 well off the bias pot is that resistor junction I take reading there its set to -37 with the pot in full clockwise position, now when I go to pin 5 etc I get -30 does that even sound right? now that I think about it doesn't lol sounds hot right? could of of swore in the past I had a closer together reading I was using a different meter though so who knows but as far as I know component values were good, some of you guys gotta have more idea about this than I do help me out please.
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Old 6th November 2012, 02:19 PM   #2
DF96 is offline DF96  England
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Grid current due to gassy valve?
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Old 6th November 2012, 11:20 PM   #3
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well before when I checked it I had the GE black-plates in so I guess I need to check it again I'm assuming and 1 of them was acting kind of gassy etc when I got that -30 reading using a different meter and I had the JJs in and I swore as low as it would go on pin 5 was like -34 so guess I need to check it again etc the GEs 1 of them would just get warm it lit up properly etc but the other one would get smoking *** hot not red-plating or anything but kind of acting like that gassy scenario where the other would get loaded down etc
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Old 6th November 2012, 11:29 PM   #4
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maybe I need to see what it is between pin 5 and pin 8? not exactly sure what voltage I should be seeing between those two?
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Old 7th November 2012, 02:17 AM   #5
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jr
can i ask what the original reason for getting in there with your trusty multimeter and checking your bias was?
and don't take this the wrong way but if you don't understand what is wrong with your statement
"maybe i need to see what is between pin 5 and pin 8?"
stop put the test leads down i don't want you or your amp to get hurt.
not knowing your skill level if your statement of having different voltages on the grids (pin 5) of your 6V6's is indeed the case you could be looking at a bad phase inverter coupling cap

Last edited by turk 182; 7th November 2012 at 02:36 AM.
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Old 7th November 2012, 03:47 AM   #6
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My bad man lol I just keep hearing something it just doesn't quite sound right like its like all of a sudden it got more harsh and like I lost bass or something kinda hard to explain lol that's why I opened her up wanted to start checking things out again.
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Old 7th November 2012, 04:01 AM   #7
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I might have messed something up though, because that Fluke I had something was wrong with it like when I checked the negative supply off the pot that resister junction network, I had it set to -37 well got like a retarded low reading like -4 lol I looked down and that GE was a smoldering red-plate from hell rofl though it was gonna blow up lol it was bad man so went and got my Cen-tek it it worked gave -37 so might have prematurely fried that ge because my meter crapped out on me lol now its acting like I messed something else up in the circuit lol
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Old 7th November 2012, 04:05 AM   #8
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not cool man lol I'm good blowing/tearing things up lol
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Old 7th November 2012, 04:20 AM   #9
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might say hell with it lol judging by how old those Caps look(Marcon) its probably getting close for cap job anyways and that's good time I can check everything else out anyways I got a nice assortment of some ELNAS and Panasonic's just dieing to be put in there xD and I want experiment with a few mods myself lol I been putting it off lol I'm gonna discharge her tonight and really go through everything see how it goes.
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Old 7th November 2012, 04:54 AM   #10
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the not quite right sound of your amp is indeed a fault
i don't want to discourage you from learning more about troubleshooting your own amp but you should make yourself and me a promise anytime if your not sure what do or what to look for and just how to test and check things stop seek help first.sometimes what you don't know can hurt
in your current situation it might be best to bring your ailing amp to a reputable service dude and see if your local library has a copy of jack darr's "guitar amplifier handbook" it's a good primer or check out the "TrainWreck Pages" online
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