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Driver tubes? What are they for?

Discussion in 'Amps and Cabs [BG]' started by, Oct 17, 2005.


    Feb 21, 2005
    So I noticed some of the Ampegs have driver tubes. What are they for?
  2. Kael


    Dec 26, 2004
    Oklahoma City
    Driving, they look especially smart with those little gloves.
  3. BurningSkies

    BurningSkies CRAZY BALDHEAD

    Feb 20, 2005
    Seweracuse, NY
    Any amp with driver tubes is a full tube amp rather than a solid state or hybrid amp.

    Most bass heads or combos that you find are a combination of two amps...a pre-amp which is the initial gain stage (or several) and a power amp.

    In the case of a 'tube amp' you'll have one set of tubes for the pre-amp and another more powerful set of tubes for the power section...the second set of tubes, are sometimes called 'driver tubes' because they 'drive' the power or 'main' section of the amp.

    If you notice, lots of amps have a 'MAIN' volume or gain and a 'PRE' volume or gain. They control each of the different sections, and different sounds can be generated by the adjustment of each.

    Driver tubes tend to be physically larger...6L6's, KT88, EL34, etc. are all usually 'power stage' tubes. While on the other hand, 'smaller' tubes like 12AX7 (the most common of preamp tubes) tend to be run in the 'pre' stage. There's a ton of different types of tubes that all work a bit differently, but most guitar and bass amps are run with a handful of tube types.

    Check out my Mesa amp:


    You can see the 12 big tubes that run in pairs across the back of the amp (in the foreground of the picture). Those are 6L6 power tubes. Each one is good for about 25 watts of power...thus making the power rating of the amp around 300 watts.

    If you look in 'front' of those tubes, you'll see 4 smaller tubes with slightly pointy tops...those are 12AX7 pre amp tubes. They amplify the initial signal and also color the tone section of the amp. The two big metal blocks to either side of the pre-amp tubes are the transformers, which feed the tubes the proper supply of electricity.
  4. Not to dispute your post BurningSkies, but there are a few hybrids using "driver" tubes. In that type of setup it's essentially a small tube power amp on a dummy load that is further amplified with a larger MOSFET power section. Warwick has been doing this with ProTube, X-treme and TubePath amps for quite a while but I am sure that there are other better-known examples. Of course you are talking specifically about Ampeg so I plead ignorance.

    Calling power tubes "drivers" in new in my book, but that doesn't mean much. :ninja:
  5. BurningSkies

    BurningSkies CRAZY BALDHEAD

    Feb 20, 2005
    Seweracuse, NY
    Nah, you're right, and I did think of it and figured someone would call me on it, but I figured why muddy the water...the kind of amps you mention are pretty few and far between, and if we're tackling 'what's a power tube', then it was probably too esoteric for the conversation. I haven't played such an amp, but have seen a few around...

    Feb 21, 2005
    Well I noticed that SVT 3 Pro has a 12AX7 and 12AU7 for their driver tubes, so you may be right.

    Thank you :D
  7. BurningSkies

    BurningSkies CRAZY BALDHEAD

    Feb 20, 2005
    Seweracuse, NY

    Those are both preamp tubes...?

    SVT 3 Pro has a Mosfet power section...They're using the term 'driver' very loosely.
  8. KJung

    KJung Supporting Member

    That's how I would define a 'driver tube'. Mesa calls this type of thing 'Simulstate'.... a tube preamp, and a tube just prior to the MOSFET SS power section in the signal chain. This supposedly makes a hybrid head sound much closer to an all tube head than a typical hybrid that usually only has a single 12Ax7 in the preamp. In Mesa's case, this seems to be the case.... the Walkabout and MPulse sound very 'tubey' to me.
  9. Plain Old Me

    Plain Old Me

    Dec 14, 2004
    I think power tubes and driver tubes are different... Don't driver tubes control the power section?
  10. BurningSkies

    BurningSkies CRAZY BALDHEAD

    Feb 20, 2005
    Seweracuse, NY

    I've always heard them used interchangably...but then it seems like regional lingo is always a bit tweaked.
  11. We could also be talking about the phase inverter that's necessary for a push-pull output section (whether tube or SS output). On my old Ampeg V4, this is a 12AU7, one half drives one side of the two 7027 pairs (the "pull" if you will), the other half drives the other side (the "push")....
  12. FireBug


    Sep 18, 2005