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6L6 vs. 7581 swap out...

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by TNJ, May 11, 2003.

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  1. May 11, 2003 #1
    TNJ

    TNJ Gold Supporting Member

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    I have a pair of matched Phillips 7581 tubes that I want to try out in a 6L6 50 watt amp. Is there any potential harm that can occur to the amp if it's not biased? I'm not an amp tech by any means, so keep it simple, o.k.? :)
    Thanks,
    S.
     
    TNJ, May 11, 2003
    TNJ, May 11, 2003
    #1
  2. May 11, 2003 #2
    VaughnC

    VaughnC Supporting Member

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    It's unlikely that you will damage the amp but, if the tubes are underbiased, they could overheat and be permanently damaged themselves.
     
    VaughnC, May 11, 2003
    VaughnC, May 11, 2003
    #2
  3. May 12, 2003 #3
    TNJ

    TNJ Gold Supporting Member

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    Thanks Vaughn...I think I will have a friend of mine do the biasing tonite with the new tubes.
    BTW....any idea on what differences are between the 7581 and 6L6?
    S.
    j
     
    TNJ, May 12, 2003
    TNJ, May 12, 2003
    #3
  4. May 12, 2003 #4
    Mark Kane

    Mark Kane Silver Supporting Member

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    They are loud, clear and IMO colder sounding. Probably fine for a preamp distortion amp.
     
    Mark Kane, May 12, 2003
    Mark Kane, May 12, 2003
    #4
  5. May 12, 2003 #5
    TNJ

    TNJ Gold Supporting Member

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    Thanks Mark!
    I'll try them out tonite and report back.
    S.
    j
     
    TNJ, May 12, 2003
    TNJ, May 12, 2003
    #5
  6. May 12, 2003 #6
    Jim Collins

    Jim Collins Member

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    I put a pair of these very tubes in my 6L6 Old Flame, replacing a pair of Svetlanas. I biased them properly, and the amp sounded better than ever. This amp is very much in the Fender blackface camp, much like a Vibrolux Reverb. They sounded so good that it depressed me when one of them shorted, and took out the heater element leads to that tube. I repaired the amp, and have been living with the old Svetlanas, since, but I'd really rather have the touch that the Phillips 7581 tubes added.
     
    Jim Collins, May 12, 2003
    Jim Collins, May 12, 2003
    #6
  7. May 12, 2003 #7
    TNJ

    TNJ Gold Supporting Member

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    Well,
    That tears it...those tubes are going in tonite.
    Thanks for the extra input.
    S.
    j
     
    TNJ, May 12, 2003
    TNJ, May 12, 2003
    #7
  8. May 12, 2003 #8
    TNJ

    TNJ Gold Supporting Member

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    Just talked to one of the guys at Two Rock...and he said that the 7581's are actually preferred over the 6L6's by some for these amps...although he liked the GE over the Phillips 7581...he did say that it was really personal taste, but to expect the same sweet tones with the Phillips as with the prior 6L6's.
    S.
    j
     
    TNJ, May 12, 2003
    TNJ, May 12, 2003
    #8
  9. May 12, 2003 #9
    VaughnC

    VaughnC Supporting Member

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    I have a couple of pairs of 7581's mainly for backups for my Komet and I think they sound pretty good. Bold & strong is how I would describe them....but in a marginal amp they might sound sterile. In my Komet they just sound bolder than most 6L6's....but my RCA 6L6 blackplates are sweeter sounding.
     
    VaughnC, May 12, 2003
    VaughnC, May 12, 2003
    #9
  10. May 14, 2003 #10
    TNJ

    TNJ Gold Supporting Member

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    I took the TR CR to my amp tech's place of biz last nite, and took along my PRS Custom 24, and my Mesa 112 M/C 90 cab. I also learned how to bias my amp...very simple procedure with the TR, you dont have to pull the chassis or anything of the sort.
    We first tried the 7581's at .050 v. Let it sit for about 10 min. , and rechecked the voltage...no drift whatsoever. I plugged in the PRS, and began playing clean...nice and chimey with that mid presence that I really love. The cleans werent quite what I was looking for, a little 'plain jane' is all I can say to describe it...not as much feel or 3D projection as I remembered with the JJ 6L6's. I remembered that one of the guys at TR recommended .055v instead of .050v...so, right befoe shutting down, I had Jeff change it to .055. Let it sit for a minute, remeasured, and plugged in. Wow! What a difference...the punch and warmth/definition all came thundering back. Dumble overdrive city, as well. I definitely had the Larry Carlton 'Last Nite' tones!
    Amazing what the bias reading can do to your tone!
    The real test will be this friday, when I take the CR (with my 212 G1265 cab) to an outdoor club gig with the rock band.
    So far, though, the tone has returned! My friend/tech Jeff was mightily impressed with both the tones and the worksmanship on this amp. He also said that these tube should last for thousand's of hours. I have another pair of JJ 6L6's coming, and am also thinking of getting a couple of RCA Blackplate 6L6's too...now that I know how to bias the amp, it's time to play a bit!
    :cool:
    S.
    j
     
    TNJ, May 14, 2003
    TNJ, May 14, 2003
    #10
  11. May 14, 2003 #11
    veldt666

    veldt666 Member

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    IMHO, Like it or not, no other 6L6 performs like a 7581. Having used them in my 50 watt combo's for years, I breifly dabbled with other types, (Ruby, GT, Sovtek, other NOS types such as WGB's, GE's, etc), each type having it's own "Signature" sound. Because my ear was accustomed to the 7581's headroom, some of these other tubes even made my amp sound like it was dying.

    I took delivery of my first "Fuchs" mod recently, which came with the latest, (I think) "Sovtek" tubes, & I got used to the amp over a two month period, loving every minute of it. I then changed out the "Sovtek's, for a pair of 7581's, biased @ .30ma. Now I have a bolder strident clean sound which I love. Sadly, as you all know 7581's wont last forever, but then, neither will I, So I'll enjoy them while I can.
     
    veldt666, May 14, 2003
    veldt666, May 14, 2003
    #11
  12. May 15, 2003 #12
    Latif

    Latif Member

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    Jato,

    Does the CR have external bias check points?. I've had to pull the chassis on my emerald and then it was easy but havn't checked my Custom as it keeps sounding so good as is. Havn't looked for external test points on it yet.

    Latif
     
    Latif, May 15, 2003
    Latif, May 15, 2003
    #12
  13. May 15, 2003 #13
    TNJ

    TNJ Gold Supporting Member

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    Latif,
    Yes, there is an external test point (+) close to the bias pot. The ground is usually one of the 1/4" jacks on the back of the amp. Biasing can be done without dropping the chassis on my Custom w/ Reverb.
    Very nice feature...
    S.
    j
     
    TNJ, May 15, 2003
    TNJ, May 15, 2003
    #13
  14. May 27, 2003 #14
    Blue Strat

    Blue Strat Member

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    7581As are great tubes and SUPER durable. They're also the cleanest of all 6L6 types.

    Most players like these though if you're looking for early power tube distortion, these may not cut it for you.
     
    Blue Strat, May 27, 2003
    Blue Strat, May 27, 2003
    #14
  15. Mar 22, 2011 #15
    guitarpedaladdict

    guitarpedaladdict Supporting Member

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    Great thread, I have two pairs of RCA blackplates (one in my amp right now), but really wanted to try out the 7581a to see if I could get a little more headroom out of my Jet Sig. Thanks TNJ for posting your experience. One thing you might want to try, if you haven't, put a 5751 in V1 on your TR - I really love what this did for mine.
     
    guitarpedaladdict, Mar 22, 2011
    guitarpedaladdict, Mar 22, 2011
    #15
  16. Mar 22, 2011 #16
    scottl

    scottl Member

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    Now up the bias to .060 and enjoy it even more!!! I never agreed with the super cold bias recommendatiosn of TR. No right or wrong. I'd try 30-35ma and see if you like it. My guess is you dig 32 (.064) or so.... Just a hunch.
     
    scottl, Mar 22, 2011
    scottl, Mar 22, 2011
    #16
  17. Mar 22, 2011 #17
    Blue Strat

    Blue Strat Member

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    They're measuring both at the same time? If so, definitely try .060 or even .070.
     
    Blue Strat, Mar 22, 2011
    Blue Strat, Mar 22, 2011
    #17
  18. Mar 22, 2011 #18
    scottl

    scottl Member

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    Yep. They often recommend 55ma for the pair. I always preferred more like 65-75 a pair. Especially with 7581 tubes!

     
    scottl, Mar 22, 2011
    scottl, Mar 22, 2011
    #18
  19. Mar 22, 2011 #19
    Blue Strat

    Blue Strat Member

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    Damn, THAT'S COLD! :D
     
    Blue Strat, Mar 22, 2011
    Blue Strat, Mar 22, 2011
    #19
  20. Mar 22, 2011 #20
    scottl

    scottl Member

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    Here Mike. In the manual too.

     
    scottl, Mar 22, 2011
    scottl, Mar 22, 2011
    #20
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