svt classic question

Discussion in 'Amps and Cabs [BG]' started by okieblues, Mar 13, 2005.

  1. okieblues


    Mar 29, 2003
    ada, oklahoma
    i recently bought a used ampeg svt 15 cab to use as a practice cab with my svt classic head. the thought was to eliminate having to drag the 8x10 around just for rehearsals. will it harm my amp to play through this 8 ohm cab with my head at 4 ohms? we're not talking major volume here, rehearsal volume is usually set around 2 to 3 on the head. thanks in advance for any replies.
  2. it shouldnt make much of a difference i wouldnt think, but i have a feeling it could be one of these things that can damage the head, probably wrong tho
    why not just switch it to 8 ohms ?
  3. okieblues


    Mar 29, 2003
    ada, oklahoma
    this particular amp only has the option of running at 2 ohms or 4 ohms.
  4. cb56


    Jul 2, 2000
    Central Illinois
    From what I've read here you shouldn't do that to a tube amp. If it was a solid state amp you'd be ok.
  5. i wasnt 100% sure but ive got a feeling like that too
  6. Joe Beets

    Joe Beets Guest

    Nov 21, 2004
    With amps, tube or solid state, you can always go with more ohms than the amp is set for. All that will happen is that you may get less power. What you you are doing when you increase the ohms is REDUCE the load on your amp. For example, if your amp is set for 4 ohms and you hook it up to 8 ohms you have REDUCED the load on the amp by half. Going the other way, however can fry your amp. If your amp requires a 4 ohm load and you hook it up to 2 ohms, you have doubled the load on the amp. There are other factors involved ,of course, like inductance and reactive loads and of course electron theory, for the electrical engineers to ponder. But in general, simple ohms arithmetic will work in most cases. ;)
  7. It doesn't work this way for tube amps because they are transformer-coupled. The impedance on the speaker side of the transformer is reflected to the amplifier side and needs to be close to the right ratio because it directly affects the operating point of the tubes.

    Running a higher than rated impedance on the speaker side is actually worse for the amp than running a lower than rated one with a tube amp. It's a bit counter-intuitive but that's the way it is...:D

    Now there's probably not much risk in mismatching from 4 to 8, most tube amps will tolerate a 100% mismatch, but I wouldn't be comfortable doing it.
  8. Bah, damned physics, biocemistry all the way
  9. Plain Old Me

    Plain Old Me

    Dec 14, 2004
    Doing this will shorten tube life... But I'm not sure running it at those volumes will do anything to the tube life...