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Posted: Wed Dec 23, 2009 8:41 pm
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With a Weber Bias Rite. :wink:


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Posted: Wed Dec 23, 2009 9:04 pm
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Yeah, that would do it. I got one almost a year ago, it's so much easier than trusting these old eyes and hands. Eladin, please indulge me one more question on your thread: Supro, did you blackface the bias circuit on your Twin? Art

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Posted: Wed Dec 23, 2009 9:18 pm
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No, I like it the way it is.


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Posted: Wed Dec 23, 2009 10:16 pm
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That's cool. Art

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Posted: Thu Dec 24, 2009 2:10 am
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aclempoppi wrote:
It seems a few current production 6V6 tubes have been beefed up to handle 450+ plate volts(Sovtek, Electro-Harmonix, and maybe JJ too). Even the old RCAs could take 425VDC for many years. Anyway, I have a question about the bias measurements you guys are using. I realize the ma current is being converted to mv through a resistor circuit, and that the two tubes are being combined before the test point. I understand the 70% dissapation principle inorder to avoid any crossover notch, but my question is about what's happening with each tube. If one measures 88mv at the test point, one is assuming a 44 ma current running through each tube, right? The assumption is based on the matching of the tubes being spot on, right? But I have found many instances of "matched" tubes being 5-6ma apart,and some even more. These are from at least five different vendors, some of which you guys mention. So, do you guys check the mv or ma on each tube? Art


As I remember, my tech says that my stock HRD was biased sth. like 56ma one tube, and 65ma the other, so no matched at all. Now both are biased at 68-69. My HRD is an European version, I don´t know if it changes sth.
By the way, the stock power tubes are GT red labels (not the white ones), I don´t know if this has sth. to be with this issue.
Merry Christmast!


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Posted: Sat Jan 16, 2010 11:58 pm
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aclempoppi wrote:
It seems a few current production 6V6 tubes have been beefed up to handle 450+ plate volts(Sovtek, Electro-Harmonix, and maybe JJ too). Even the old RCAs could take 425VDC for many years. Anyway, I have a question about the bias measurements you guys are using. I realize the ma current is being converted to mv through a resistor circuit, and that the two tubes are being combined before the test point. I understand the 70% dissapation principle inorder to avoid any crossover notch, but my question is about what's happening with each tube. If one measures 88mv at the test point, one is assuming a 44 ma current running through each tube, right? The assumption is based on the matching of the tubes being spot on, right? But I have found many instances of "matched" tubes being 5-6ma apart,and some even more. These are from at least five different vendors, some of which you guys mention. So, do you guys check the mv or ma on each tube? Art



well i,m using a amp- head bias probe,that measures tube current and plate voltage,my amp plate voltage is 435 and i have jj 6l6 's,so the calculated mv for plate voltage was between 85mv mildly warm to 90mv hot,so i went to 88mv and the tubes are sounding great!eurotubes state that they can run up to 95mv,but tube life would be shortened but amp would breakup pretty darn good,but then you sacrifice tube life!...for 6v6's they recommend i would bias 35 to 40mv..even up to 45mv if bias would go to that with 6v6 installed,depends on amp,some will.. some won't get 45mv without a resistor change.

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