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Can I plug in an additional cabinet when an amp is on?

Discussion in 'Amps and Cabs [BG]' started by Dan Pomykalski, Nov 7, 2018.


  1. If I have a tube amp that outputs 4ohms plugged into an 8ohm cabinet, is it bad to plug another 8ohm cabinet into that cabinet in parallel while the amp is on and off standby? Would it be bad to remove the second cabinet with the amp on and off standby?
     
  2. The output is in Volts or Watts, which is affected by Impedance, but the output is not measured in Ohms.

    If there is no output during those times, it will be fine, but why not run both cabinets at 4 Ohms, if that's how the amp is rated?
     
  3. Gravedigger Dav

    Gravedigger Dav Supporting Member

    Mar 13, 2014
    Fort Worth, Texas
    I don't think it would hurt anything, but I wouldn't do it. I have a habit of turning everything off if I make any changes to an electric circuit. Just OCD from military electronics training.
     
  4. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    Probably not a problem but not a good practice in general for tube amps.
     
  5. beans-on-toast

    beans-on-toast Supporting Member

    Aug 7, 2008
    If using a ¼” speaker cable there is a possibility that you could momentarily short the output of the amp. It could also cause a loud pop which isn’t good. With a speakon, there shouldn’t be a shorting issue.

    Why live life dangerously. Be safe and put the amp in standby before mucking around with the speaker cables.
     
  6. Two of my tube amps don't have a standby switch. Since turning an amp on, then off, then back on, then possibly back off and on again isn't great for tubes, I figured if adding a cabinet while the amp was on wasn't hurting anything, I'd save the tubes if possible.
     
  7. ThisBass

    ThisBass

    Aug 29, 2012
    Germany
    Theoretically if the (+) terminal carries the same voltage as the (-) terminal then a short between the both would mean absolutely nothing. In this case there was no current flow from (+) to (-) even if there was a short between both terminals.
    You want to turn the volume knobs of the amplifier counterclockwise all the way down just to mute the amplifier, thus the output (+) termal carries very little (noise) voltage versus the (-) terminal. In the case of a short there was only little current flowing cause noisefloor output voltage of a muted amplifier is (almost always) very small.
     
    Last edited: Nov 7, 2018
    pellomoco14 and Dan Pomykalski like this.
  8. beans-on-toast

    beans-on-toast Supporting Member

    Aug 7, 2008
    I don’t suspect that you’ll be doing this very often. I wouldn’t be overly concerned about doing it once in a while.

    Turning the amp off, switching the speaker output, then turning it back on will stress the tubes less than power up when they are cold.

    Without a standby switch, it’s common sense to turn the amp off when switching cabs.

    Some tube amps have a speaker out jack that shorts the input when there is no plug in the jack. This helps protect the amp. A tube amp prefers a short cross the output over an open circuit. Not all tube amps have this feature.
     
    Last edited: Nov 7, 2018
  9. Ehh, you just get a pop. Whether or not you think that's cool or not is on you.
     
    Last edited: Nov 7, 2018
  10. Agreed.

    However, in standby there should be no plate voltage for the tubes to be dong anything (output-wise).
    But just because you can, doesn't mean you should.
    Sometimes a habit developed with one amp might be what kills another.
    Two switches off is a greater margin of safety than one switch off.
    I know it's a PITA to wait for the warm up, but it's not like you are changing cab configs mid gig, are you?
    And filaments being off for just a few seconds while you plug/unplug will get you back to fully warmed up much quicker than from a cold start.
     
    Gravedigger Dav likes this.
  11. Right! :thumbsup:

    Tube amp! You should run the proper load. Otherwise the poor tubes might be working over-time (harder than normal) to get you what you want.
     
    Killed_by_Death likes this.
  12. JimmyM

    JimmyM Supporting Member

    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    Turning it off and on once is better for tubes than shorting the output section while fiddling around with the speaker cable.
     
    sharkbait130, HolmeBass and rodl2005 like this.

  13. What do you mean by “doing this?” Turning the amp on and off repeadetly, or adding and subtracting cabinets.

    Also, I wasn’t asking about whether or not I should turn my amp off when I’m switching cabinets. I was wondering if it was bad for the amp to add an additional cabinet or unplug one of multiple cabinets while the amp’s on.
     
    beans-on-toast likes this.
  14. I don’t really care about having to wait for the tubes to get warm. I’m trying to figure out what stresses the amp more; turning it on and off while I test a bunch of different cabinet configurations, or adding and subtracting one of multiple cabinets while the amp’s on.
     
    pellomoco14 likes this.
  15. It isn’t once though. I have eight cabinets that I swap the speakers in and out of. While experimenting with what sounds best, I could turn the amp on and off anywhere from dozens to hundreds of times probably.
     
  16. K
     
  17. arbiterusa

    arbiterusa

    Sep 24, 2015
    San Diego, CA
    You can do anything you want if you put your mind to it.
     
    Balog, sprag, pcake and 2 others like this.
  18. I guess I missed the fact that you were doing this to test a bunch of different cabinets.
    In that case, what I would do is take the number cabinets that you have to test and divide that number into the amount if time you have to test them and let the math decide.
    You may not only get to test a bunch of different cabs, but also might be able to answer the question of which causes more stress.
    Good luck and please post your stress results.
     
    HolmeBass likes this.
  19. Actually, you can try to do more things if you don’t put your mind to it. ;)
     
  20. Doing this is not necessarily cumulative. You are not allotted X number of tries before failure. It could happen on number three, it could happen on number three hundred. There is no formula.
     
    gregmon79 and JimmyM like this.

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