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tube amp load connection

Discussion in 'Amps and Cabs [BG]' started by metron, Apr 19, 2005.


  1. metron

    metron Fluffy does not agree

    Sep 12, 2003
    Lakewood Colorado
    Ive heard that a tube amp must always be hooked up to a load. My question is when is this essential? I usually fire up my amp in standby, let it heat up, then jam but hook up the speaker before I turn it on. Can the amp be on without the load connected if its in standby? What about if its not in standby but you arent playing yet. Is that ok? I guess the question is at what point will you do damage by not having a load connected. Thanks!
     
  2. Ben Clarke

    Ben Clarke Liquidating to fund a new business. Buy My Gear!

    Jan 6, 2005
    Western NY
    In standby, all is good. I couldn't think of a reason to take it out of standby with no load.
     
  3. Plain Old Me

    Plain Old Me

    Dec 14, 2004
    +1, taking it out of standby without a load will damage the plates.
     
  4. metron

    metron Fluffy does not agree

    Sep 12, 2003
    Lakewood Colorado
    So its ok to not have a speaker connected when the amp is in standby? The reason is because I want to swap cabs and not have to turn the amp off. Also does it hurt to switch the impedance tap while in standby?
     
  5. Plain Old Me

    Plain Old Me

    Dec 14, 2004
    I'm pretty sure you can do just about anything you want while its in standby.
     
  6. Wesley R

    Wesley R Supporting Member

    Check with the folks over here

    http://www.webervst.com/vstbbs/bbs.html

    They live and breath tube amps. The amp section gets a lot more attention then the bass section, I would post the question in the amp section.

    Best of Luck,
    Wesley R.
     
  7. Jerrold Tiers

    Jerrold Tiers

    Nov 14, 2003
    St Louis
    In "standby", generally the tube filaments are on, and the bias and preamp power may or may not be on.

    High voltage to the output tubes should be "off" in standby.

    That said, I seem to recall a few that did something else, like short the signal out before the output tubes, etc. That might or might not be equivalent.

    Tube amps that have output transformers need a load to avoid large "spike" voltages that might damage the tube, the transformer, or other parts. A 500V plate voltage might result in 3000V or more of spike voltage, depending on exact conditions. That can puncture insulation, induce arcing, etc.

    They may also need a load to avoid internal feedback that causes high frequency oscillations. That can degrade a tube in a few seconds, before you can hit the switch. If the plates glow orange, the tubes have been damaged, almost certainly.

    Just about every tube amplifier has an output transformer, so for your purposes, yes they need a load anytime they are fully powered up and can pass a signal.

    In standby, you should be able to swap cabs, etc. Just don't forget to put it in standby.

    (Added for "completeness": There are a few tube amplifier designs, generally on the audiophile fringe, that don't use output transformers. Futterman, for instance. They wouldn't need a load, necessarily, but every other type does.)
     
  8. Ben Clarke

    Ben Clarke Liquidating to fund a new business. Buy My Gear!

    Jan 6, 2005
    Western NY
    Hmmm.. I wonder if I could borrow my friend's Atmaspheres for our next bar gig? I'm guessing no! :crying:

    Nice complete answers here. :hyper:
     
  9. metron

    metron Fluffy does not agree

    Sep 12, 2003
    Lakewood Colorado
    You guys are awesome! Im using a 70s ampeg V-4B. I just wanted to make sure I wouldnt damage anything if I switch 4 and 8 ohm cabs while in standby. Sounds like its ok to do. Thanks again! :bassist:
     
  10. tombowlus

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

    Apr 3, 2003
    North central Ohio
    Editor-in-Chief, Bass Gear Magazine
    On a related topic, when a tube amp is in standby, is this putting any significant wear on the power tubes, and/or does it shorten their lifespan? For instance, if I were to playing through an all-tube combo, and I hit standby, I might leave it like that while I get a drink or a bite to eat (20-30 minutes), so that when I come back, the tubes are still warmed up and sounding purdy. But, if I were going to leave for a longer period of time, how long is long enough to say "turn that bad-boy off and save those tubes!"?

    Thanks, Tom.
     
  11. Some people think that an amp in long term standby (weeks or months continuously at minimum) will develop a "coating" of stray electrons on the cathode and reduce its emission. For a few minutes, don't worry about it.
     
  12. jokerjkny

    jokerjkny

    Jan 19, 2002
    NY / NJ / PA
    actually, as long as you completely lower the volume on your bass, or the master volume, you should be able to swap and do whatever. as long as no signal is passing thru, you shouldnt damage anything.

    but i wouldnt recommend for guys with bad short term memories, cause mistakenly strumming your bass while accidently touching the speaker lead doesnt sound like fun. :meh:
     
  13. Jerrold Tiers

    Jerrold Tiers

    Nov 14, 2003
    St Louis
    "Should" covers a lot of ground here...lots of things "should" work.

    But it "CAN" cause damage for those amps where a load is necessary to keep the unit from oscillating.

    Problem is the negative feedback in the power amp can shift phase and become "positive" feedback when the load is disconnected.

    It's simple enough to hit the standby switch when there is one.
     
  14. jokerjkny

    jokerjkny

    Jan 19, 2002
    NY / NJ / PA
    ooo,

    thx jerr. good things to know... :cool: