running without load?? help

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by Jimbob, Jul 12, 2004.


  1. Jimbob

    Jimbob Guest

    hey, i'm a dumbass.

    today i was jamming and i had to move my amp to a different house.

    once i had it setup, i flipped the power switch on, and left it in standby for about 3-5 minutes.

    then i turned the standby on, and couldn't figure out why i didn't have any volume. took me about 15 seconds to realize i didn't have the speakers plugged in.

    i turned it off, plugged em in, then turned it back on. jammed for an hour... seemed to work just fine...

    it was a soldano decatone head btw.

    I know, i'm a dumbass. that said, could the amp be damaged? I mean, if anything had happened, would it be painfully obvious? or could it have like, i dunno, killed 50% of my tone forever or something? do these newer heads have any sort of mechanism to protect against running no load, like the line 6 heads that disconnect whatever when there are no speakers plugged in?

    like i said it sounded fine after i plugged the speakers in, but now my brain is going and i want to technically know what occurred. please help. thanks.
     
  2. VaughnC

    VaughnC Supporting Member

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    With no load on a tube amp, the sonic energy has no place to disspate so it is reflected backwards towards the amp and stepped up in voltage in the process. Said reflected voltage can then arc between the output transformer's windings and its case, breaking down the insulation, which can give the power supply voltage a short path to ground, taking out the output transformer in the process. Also, the output tube sockets can arc, creating carbon trail voltage leakage.

    However, it requires a fairly high volume for all this to happen and it's unlikey that you did that in 15 seconds. Also, I'm not sure how Soldano's are wired, but some amp manufacturers use shorting type speaker jacks which prevents a voltage build up without a plug plugged into the speaker jack. Of course, this protection is defeated if you plug a cable into the speaker jack and the other end of the cable isn't connected to a speaker.

    Chances are that you didn't do any damage to the amp in that short of time but just keep on the lookout for anything unusual.
     
  3. Jimbob

    Jimbob Guest

    thanks!

    yeah, i didn't have a plug in the jack at all. I cranked it again a little while ago and it seemed ok.

    Three quick questions if you wouldn't mind:
    1) is the only critical time for no-load damage when the amp is fully on, ie not in standby? would that 3 minutes of power, but on standby, have done anything in theory? Im just curious.

    2) the amp did this since I got it new; sometimes if i turn it on and up a bit, and disconnect the instrument cable from the input jack (so that there is nothing plugged into the input), it will make these sort of random, scratching/muffling noises, kinda like someone's rubbing the other end of an instrument cable against their shirt. it kinda comes and goes and isn't very loud or anything, but audible. is this normal behavior? does not do it when something is plugged in I dont believe.

    3) When playing in a room that has ****** wiring, you know, sometimes I'll get that bad grounding thing going on, for lack of a better word, where you get hum if your hand isn't on the instrument's metal or whatever. I realize this is just a limitation of some rooms, but does it have any negative effect on the amp other than the hum?

    Thanks a ton.
     
  4. spaceboy

    spaceboy Member

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    ahhhh, I thought that was because there was something wrong with the grounding of the guitar! yay - my guitar's fine! but the wiring of my bedroom obviously isn't...

    cheers!
     
  5. Jimbob

    Jimbob Guest

    yeah man :)

    When I bought my first single-coil bass it REALLY became apparent, and I thought the instrument wiring was off... but later I realized it only did it in my house with ****** electrical wiring, if i went somewhere nice like my parent's house there was no grounding issue.
     
  6. spaceboy

    spaceboy Member

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    actually, I just happened to be screwing the trem claw farther in for increased tuning stability when i noticed that the ground wire wasn't actually attached to the claw! it had the big blob of solder on the end, but no connection. i spent ages trying to get it to hold - and it just bloody wouldn't. would just slide off again. argh! so maybe I do have a grounding issue... i think I'll start my own thread about this...

    PS. your amp'll be fine :D
     

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