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Blue Tube 903 pedal - swapping tubes, pots, etc....

Discussion in 'Effects [BG]' started by gfab333, Aug 29, 2003.

  1. gfab333


    Mar 22, 2000
    Honolulu, Hawaii
    Alright this thread is for all those interested in sharing or learning about the tonal possibilities related to swapping different tubes through the Blue Tube 903 pedal. Blue tube rack mounts and others are welcome to chime in.

    Just as background, I'm not going for an actual overdrive fuzz tone. I usually play R & B, funk, 70s & Motown, and current top 40 cover tunes, so I go for a clean punchy tone using my GK / Eden / EA rigs. Once in awhile, I jam with some old school 1960s style classic rockers, and I find that my rigs are too clean and punchy. So, rather than buy an SVT, I thought I'd try a tube preamp / overdrive pedal. I seem to be getting close to the tone that I'm looking for, just by dialing in a little overdrive for warmth and grit.

    My 903 pedal came with a cracked Ruby 12AX7, which I never got to hear for obvious reasons. A friend immediately got me a used Mullard 12AX7. This sounded OK, it seemed to have a bump in the lower mid-bass, slight harsh overdrive when the drive nob is tunred up. I think this tube may have been better suited for lead guitar.

    Next I bought a Groove Tube 12AU7. Slightly less gain, warmer than the Mullard for bass, nice understated overdrive. I try to get some samples up in this thread this weekend (already have one up in another thread).

    I'm also interested in trying a 5751. I've heard from some bassists that claim this one has nice warm lows.

    This weekend a bassist/guitarist tube guru-type is gonna provide me with a 12AY7. He claims it might get me closer to the B-15, Bassman, kind of tone (yeah, yeah, I know I should go buy one of those heads). Anyway, we'll see how it goes.
  2. gfab333,

    I've got a five year old 903 which I scored at a closeout here in Chicago at Guitar Center for $75! I don't use it much anymore, but the tube swapping has gotten me interested. Also, how do you feel about the EQ flexibility, it's ranges, etc., since it wasn't specifically designed for bass? Any noise noticeable? Mine has kind of a very light low freq hum when engaged, kind of like bad filter caps in an amp. But you can't hear it in a normal performance environment.

    I decided to lay off of it a while back, and haven't used it for a while. It seemed to compress out some of the attack of my primary instrument, a StingRay 5. But I should experiment more, I suppose.

  3. Showdown

    Showdown Supporting Member

    Jan 21, 2002
    Honolulu, Hawaii
    Aloha gfab333,

    I use to use one. The problem I had was trying to get decent volume without too much overdrive. With the output on "10", I would have to turn the drive up to about "6" to get the same volume as with the effect off, but then there was too much distortion.

    The 12AU7 sounds like it might have worked better for the sound I wanted out of it.
  4. gfab333


    Mar 22, 2000
    Honolulu, Hawaii
    I was able to try the 903 with the RCA 12AY7 at a jam session. It definitely changed the overall tone of the pedal. With all factors constant as far as volume and tone settings on the pedal and amp, etc., the RCA 12AY7 seems to have a bigger deeper bottom than the GT 12AU7. The warmth and overdrive characteristics seem to be about the same. As far as gain/drive, I know that the 12AY7 has less gain the the 12AX7, but I don't know where it stands relative to the 12AU7. I was able to dial-up a very nice "Classic 60s rock" bass tone, with just a very slight bit of grit and drive. This subtle overdrive would particularly surface when you dig in to the strings.

    Anyway, this is alot closer to the tube-style tone that I've been looking for. My friend advised me that the 12AY7 is the first tube in the preamp stage that Fender used to install in the old 1950s tweed Bassman.

    This confirms my suspicion that different tubes not only possess different overdrive characteristics, but they also have different tonal characteristics as far as bass, mids, and highs.

    I'll try to get a sample up soon.

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