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Thread: Tube question

  1. #1

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    Default Tube question

    I have a tube integrated amp it uses (4) 6V6's for output tubes and (2) 6SL7's for input/driver tubes. The amp is manually biased by (4) pots, one for each output tube.

    My question is, when I change input/driver tubes do the output tubes bias change significantly? Should I re-bias the output tubes every time I change input tubes or will the input/driver tubes not affect the bias of the output tubes that much?

    I rolled in a NOS pair of 1948 Tung-Sol JAN-CTL-6SU7GTY pair in tonight to make sure they work since I just bought them. The prior tubes were RCA 5691 "red base" and the bias really didn't change at all. Is this typical or did I just get lucky? It's a slight PITA to bias this amp and if I can avoid the hassle when I roll the RCA's back in that's fine by me.

    Looking for first hand-knowledge and opinions. It seems to me in a SS amp changing the input/driver tranny's would affect the output tranny's, but maybe for a tube design that's not true.

    I will say there is a night and day difference in sound between the RCA red base 5671 and the TS 6SU7GTY.

    H9
    "Appreciation of audio is a completely subjective human experience. Measurements can provide a measure of insight, but are no substitute for human judgment. Why are we looking to reduce a subjective experience to objective criteria anyway? The subtleties of music and audio reproduction are for those who appreciate it. Differentiation by numbers is for those who do not".--Nelson Pass

    Pass Aleph 30; Eastern Electric Mini Max; Adcom GDA600; MIT S3/Z Pc; SDA 1C; Squeezebox; Tubes add soul!

  2. #2

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    The better the tube amp the less I've found the need to bias. I usually bias after every complete retube but not much after that unless the soundstage noticeably shifts. If you're staying with the same tube and not using a substitution with different plate voltage, etc...you should be fine.

    I had a Radii amp that had to be biased everytime you thought about turning it on...and then after you touch it, then again after you went to the bathroom. It was ridiculous.
    Last edited by dorokusai; 01-20-2010 at 10:52 PM.

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    That's the thing the RCA 5671 is a ruggedized version of the 6SL7 and the Tung Sol JAN 6SU7GTY is a military version of the 6SL7 and they both have pretty much identical characteristics. Probably why I didn't see a change in the bias. I've run the amp for a couple hours now and just rechecked the bias and it's right where it was when I powered it on.

    Guess I'll close her up and burn the Tung Sol's in and see if I want to keep them.

    Thanks
    "Appreciation of audio is a completely subjective human experience. Measurements can provide a measure of insight, but are no substitute for human judgment. Why are we looking to reduce a subjective experience to objective criteria anyway? The subtleties of music and audio reproduction are for those who appreciate it. Differentiation by numbers is for those who do not".--Nelson Pass

    Pass Aleph 30; Eastern Electric Mini Max; Adcom GDA600; MIT S3/Z Pc; SDA 1C; Squeezebox; Tubes add soul!

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    Quote Originally Posted by heiney9 View Post
    That's the thing the RCA 5671 is a ruggedized version of the 6SL7 and the Tung Sol JAN 6SU7GTY is a military version of the 6SL7 and they both have pretty much identical characteristics. Probably why I didn't see a change in the bias. I've run the amp for a couple hours now and just rechecked the bias and it's right where it was when I powered it on.

    Guess I'll close her up and burn the Tung Sol's in and see if I want to keep them.

    Thanks
    I wouldn't think twice about it, just enjoy and check it in a week.

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