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Art Tube channel tube rolling

Discussion in 'Amps and Cabs [BG]' started by 2milehighspike, Oct 17, 2020.

  1. 2milehighspike

    2milehighspike Supporting Member

    Greetings all, I have an Art Tube Channel that has 2 12ax7a tubes. Ther has always been a slight hiss but it has gotten worse recently and I am thinking I might swap the tubes. I am looking for the quietest set and not looking for any overdrive, just warmth. After some research the 12au7 tubes might be what I’m looking for but I am by no means a tube expert. So any advice would be appreciated. Thanks
  2. rickdog

    rickdog Gold Supporting Member

    Mar 27, 2010
    I'd be dubious about changing tube types. Substituting different tubes in a preamp or amp that's being operated for its "character" (meaning, may be driven into at least mild distortion) can be useful. But the Tube Channel is meant to be more in the line of studio gear that's run pretty clean; and you aren't looking for any overdrive. My guess (and it's only a guess) is that you're more likely to lose than gain in the swap. 12AX7 and 12AU7 have vastly different gain and operating points.

    Rather than switching types, consider simply switching brands (and getting brand new tubes in the process). Just because the tubes are running relatively clean, it doesn't mean they don't have any effect on the sound. If I were going to try tube rolling in that unit, I'd probably try a JJ ECC803S and a New Sensor TungSol reissue 12AX7. Fortunately, good preamp tubes can be found in the $12-$20 price range, so experimenting isn't very costly.

    I used to have a Tube Channel, and really liked it (actually, not for bass, but as a mic preamp for a vocalist I was working with). Sadly, it was stolen... happily, the meth-heads that took it didn't touch my two favorite basses sitting a few feet way.
  3. Try a pair of 7025 to see if they help.
    2milehighspike likes this.
  4. starjag

    starjag Supporting Member

    Dec 3, 2019
    7025 or 12AT7 are the options to try. You can still find old Jan Phillips 7025 at good prices.

    quickfix and 2milehighspike like this.
  5. 2milehighspike

    2milehighspike Supporting Member

    What got me into the Tube Channel in the first place was when my MBF800 was stolen between sets at a gig. I was thinking about the 12au7 tubes because( I may be wrong) that they were used in SVTs. I know that the TC and SVTs are completely different animals though.
  6. 12AT7/ECC81 have less gain than the the 12AX7/ECC83 variants. 12AU7/ECC82 have even less.
  7. Wasnex


    Dec 25, 2011
    Although you can stuff a 12AT7 or 12AU7 in the pre, I would suggest sticking with 12AX7. The tubes are self-biasing, and each has a different bias point. So a circuit designed for each of these tubes will have different resistors to set the bias points. Yes you can often sub in a different tube type, but the tube will not be working in the optimum point of it's operating curve.

    FYI the gain for various 12AX7 models actually varies a bit. The Tung Sol is one of the higher gain 12AX7s. That won't necessarily mean it's noiser. The noise in your preamp may be because the tube is not operating properly. JJ offers a medium gain ECC83S MG, and 5751 is considered a low gain sub for 12AX7. 7025, ECC83, ECC803 are all subs for 12AX7. There are more models if you consider vintage tubes, but these are the common model designations that are still in production.

    My advice is try rolling some fresh tubes into the preamp. If it is still noisy, it may have a bad component that is the source of the noise. Rolling a lower gain tube such as a 12AT7 or 12AU7 may mask the noise problem, but there may be other consequences.

    I have a couple of amps that some people like to roll lower gain tubes into. I preferred 12AX7s, even over NOS 5751s. To me the 12AX7s were more lively and musical. The 5751s did not sound bad, but were sort of dull and lifeless in comparison to 12AX7s. That doesn't mean you should not try a 5751, since taste is subjective.

    Even I have one circuit that was designed for 12AT7 that is running a 12AU7. It's the reverb driver on my 1968 Fender Showman Reverb. This is a very common sub on Fender amps. With the 12AT7 the Reverb control is very hard to dial in because the gain is too high. This is especially problematic on my amp, because the control has a dead spot from years of use. With the 12AU7 I can run the control above the dead spot and I even like the sound better; it's not as splashy. So in this case, I find making the sound a little less lively preferable.

    Good luck and have fun!
  8. 2milehighspike

    2milehighspike Supporting Member

    Thanks for the info gents. After doing a little research I may go with the EH 7025. The Tube store has them for abut $40 matched. I may settle on another 12AX7 set since I have several guitar amps I can try them on.
  9. Wasnex


    Dec 25, 2011
    This sampler has some of my favorites:
    Vacuum Tube Set - 12AX7 Sampler, 8 total tubes

    $110 for 8 tubes = $13.75 average price per tube. You'll definitely spend more if you buy the same tubes individually.
  10. The 12au7 is the driver tube. Its after the preamp. Used to gain stage the power section.

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