1. Please take 30 seconds to register your free account to remove most ads, post topics, make friends, earn reward points at our store, and more!  
    TalkBass.com has been uniting the low end since 1998.  Join us! :)

Purpose of a driver tube?

Discussion in 'Amps and Cabs [BG]' started by FireBug, Oct 3, 2005.

  1. FireBug


    Sep 18, 2005
    This might seem a little self-explanatory but, what exactly does a driver tube do? In relation to power tubes?
  2. I'm just taking a shot here. I used to know the answer in absolute terms, but it's been a while since I was heavy into circuitry.

    The driver can/does act as another gain stage (after the pre-amp) to provide the proper values to the input of the power stage. But more importantly, it serves to present the correct part of the waveform (positive or negative relative to 0 volts) to the correct tube or pair of tubes. This is where I run out of steam, but I'm mainly thinking of Class AB tube amps, where part of the (power) amp boosts the positive side, the other the negative. I don't remember how it works with the Class A types. I'm sure we'll get clarification, though.
  3. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    If by a driver tube you mean a pre-amp tube, simply put it boosts signal voltage while power tubes boost current.
  4. from the limited knowledge I have in this field, I believe whacker is correct in stating that the driver tube is located post preamp, but before the poweramp... apparently this type of design (SVT3-PRO and SVT-6 PRO) is supposed to give a slightly more similar tone to an all tube amp than your average hybrid with only preamp tubes?
  5. brianrost

    brianrost Gold Supporting Member

    Apr 26, 2000
    Boston, Taxachusetts
    The "driver" in an all tube amp is also known as the "phase inverter" which is needed for push-pull amp designs (i.e. one half of the power amp PUSHES the speakers OUT and the other half PULLS the speakers IN).
  6. Ed Fuqua

    Ed Fuqua

    Dec 13, 1999
    Chuck Sher publishes my book, WALKING BASSICS:The Fundamentals of Jazz Bass Playing.
    Isn't that the one that makes sure all the other tubes get to the gig?
  7. tadawson


    Aug 24, 2005
    Lewisville, TX
    The driver tube has a couple of functions, the main one of which is to get the preamp output to the appropriate level to drive the output power tubes, as well as to provide isolation from the preamp to the poweramp. The preamp stages are primarily for gain and singnal processing - tone, reverb, etc, and the driver stage is all about generating enough signal to drive the outputs, since the preamp tubes cannot typically provide enough drive to run the finals. There is frequently also a phase inverter associated with the driver tubes, but they are separate, but related functions.

    - Tim
  8. Jerrold Tiers

    Jerrold Tiers

    Nov 14, 2003
    St Louis
    Most tube amps really don't have "driver" tubes. They have phase inverters etc.

    Only amps such as the SVT that really push the power tubes (drawing grid current) need a real "driver" tube. The output tube needs to draw actual "power" and not just a voltage from the previous stage. The "driver" tube provides that power.

    More generally it would be the tube(s) whose main purpose is to provide the power tube grids with what they need, signal-wise. Could include phase-splitter tubes, for instance.

    That is as opposed to a preamp tube that provides voltage gain or EQ etc, as its main task, etc.
  9. tombowlus

    tombowlus If it sounds good, it is good Gold Supporting Member

    Apr 3, 2003
    Fremont, Ohio
    Editor-in-Chief, Bass Gear Magazine
    LOL!!! :D
  10. Jerrold Tiers

    Jerrold Tiers

    Nov 14, 2003
    St Louis
    Yow.... how did I miss that one?