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HELP! I just set my amp on fire!

Discussion in 'Amps and Cabs [BG]' started by johnbegone, Mar 16, 2005.


  1. johnbegone

    johnbegone

    Sep 16, 2004
    Chicago, IL
    OK, so I use an Ampeg SVT-3Pro and have for about 8 months now with no problems. I usually use it through two ampeg 4x10s (8ohm each for a 4ohm load... I'm not sure if this matters yet with my problem). So just yesterday I bought a 70's Ampeg 8x10 which is rated at 4ohms. When I bought it I plugged MY amp in and tested it and it sounded wonderful and all was well. Today I got it back in my house and was testing it out again, it was sounding loud and awesome and then all the sudden the amp shut down and the fans kicked into high gear. Obviously I freaked out and shut the thing off ASAP. A few minutes later I decided to turn it back on (stupid) at this point the lights on the front of the amp started flickering and then inside the amp I heard the sound of something small being set on fire and I saw a couple flashes of light from behind all the knobs. I turned it off and unplugged anything that was plugged into it (all cables, etc) and after a few minutes it started smelling like burnt electronics..........

    I'm about to take it all apart and see if I can tell what happened, but I am by NO means an amp expert. Has this thing happened to other people, if so what are the possibilites as to WHY this happened and what can I do to a) fix it and b) prevent it from ever happening again.

    Things I've thought of: maybe the 8x10, since it's so old, got rewired along the way and is at less than 4ohms, but I don't know if this would cause this reaction in such a short amount of time of having the amp going (about 5 minutes).

    Maybe a preamp tube blew out?

    Maybe I blew the transformer?

    Any help is MUCH appreciated. Thanks guys.
     
  2. Warwick player

    Warwick player

    Dec 31, 2002
    Bucks, UK
    You didn't have any other speaker cabs connected when you were testing it? :meh:

    Just remember to unplug it from the wall when you do go in there and ensure any capacitors have had time to discharge! Even though you have unplugged it they can still hold a nasty shock if you don't know what you are doing. :(

    Good Luck and be careful
     
  3. johnbegone

    johnbegone

    Sep 16, 2004
    Chicago, IL
    Nope, I just had the one cabinet plugged in. I just took the cover off and looked around and I can't see anything out of the ordinary..... I looked at all the tubes (5) and they seem OK? I don't know much about tubes, but they didn't seem like they had been on fire ever. I'm pretty confused right now.
     
  4. Sutton

    Sutton

    Mar 3, 2005
    Plainwell, MI
    did you try it again with the old cabinets connected to it?
     
  5. johnbegone

    johnbegone

    Sep 16, 2004
    Chicago, IL
    I have NO intentions of plugging this in again until I figure out what could be the problem. So, no.
     
  6. Sutton

    Sutton

    Mar 3, 2005
    Plainwell, MI
    Ok, well are you positive that it was the head that did all this?? I just find it wierd that all this happened, when you tried an used cabinet that you just got.
     
  7. johnbegone

    johnbegone

    Sep 16, 2004
    Chicago, IL
    I'm open to the possibility that the cabinet caused the amp failure, but regardless, the amp was on fire so I'm not plugging in back in.
     
  8. Warwick player

    Warwick player

    Dec 31, 2002
    Bucks, UK
    I don't think it would be smart to plug the other cabs in! ;)

    Can you identify the area where you saw the lights or sparks coming from?

    Does it have any fuses in there which could have blown?
    Do you have any test gear you can check components over with?
     
  9. Sutton

    Sutton

    Mar 3, 2005
    Plainwell, MI
    How sure are you with the fire claim? Because if it was a spark, its not always an expensive thing, fires are almost always expensive
     
  10. johnbegone

    johnbegone

    Sep 16, 2004
    Chicago, IL
    It was definitely more of a series of sparks (two maybe?) then a fire. I mean... there were never flames, so I may have over-dramaticized that aspect. and I don't really have any test equipment. The sparks were seen on the left side of the amp (where all the preamp tubes are).
     
  11. Sutton

    Sutton

    Mar 3, 2005
    Plainwell, MI
    Hmm, ok Well if you dont know alot about amps, I wouldnt recommend you opening it up and playing around with it too much, except to maybe look for burn damages.

    My experences with Ampeg hasnt been exactly well. I've seen and heard stories of them doing stuff somewhat similar to this. There tone is great, but the quality has seemed to go down in the last years.

    I'd recommend that you just send it off to a guitar shop near by, and explain to them what happened, and see if they can figure out the problem
     
  12. Passinwind

    Passinwind I Know Nothing Supporting Member

    Tubes don't catch on fire. Transformers don't blow very often at all either. Your amp has a solid state power amp, and that's likely to be where the problem happened. Since a "new" cab coincides with the failure, expect impedance issues to be at the root. I'd open up the cab, and meter out all the wiring in it. You can start by metering at the speaker cable though, without opening anything up. If you don't own a meter, buy one, they're cheap. Every electric musician can benefit from having one. Look for a short somewhere in the wiring, an open would be far less likely to cause these symptoms. I'd guess that either a driver shorted, or the cab has non-original drivers installed. The amp could've just decided to fail at this time coincidentally though.

    You could be lucky, and maybe a small resistor cooked. More likely, power transistors or power supply components did. You'll need to get the amp, and preferably also the cab, to a technician at this point. Don't poke around in the amp and make things worse. Don't turn the amp back on, at all, unless you have a Variac and the skills to know what to do with it. When I was in the repair biz, I saw way too many pieces that someone had tried to self-diagnose, and had screwed up.

    I've been promising IvanMike to write a little tutorial on self-diagnosing gear, and I've been slacking miserably in getting it done. I'll see if I can do better with that. Good luck, and be careful!
     
  13. johnbegone

    johnbegone

    Sep 16, 2004
    Chicago, IL
    Passinwind, thanks for the input. Now that you mention it, one of the drivers had been replaced with a new one from Ampeg. So it's got 7 old old drivers and one new. I'm working on taking the speakers out to check individual impedance ratings and to check how it's been rewired after that switch.
     
  14. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    My understanding of the Ampeg 810's is they have 8 drivers of 32 Ohms each, all wired in parrallel to get a 4 ohm load. If all drivers are 32 Ohm, there isn't a wiring combination possible to get below 4 ohms. If the replacement driver anything other than 32ohms, we may have found the cause of your problems.

    I suspect that whoever replaced the driver has assumed all Ampeg 10's are the same, the store had some 8 ohm 10's in stock, so that's what they used.

    Checking the resistance of each driver is a good idea. Remember that you're actually measuring DC resistance, so they won't read 32 ohms exactly. Typically a speaker with 8 Ohm nominal impedance will read aproximately 6 Ohms DC resistance, so I suspect a 32 Ohm speaker should read somewhere in the 20's.

    It probably wouldn't hurt to also test the DC resistance of the entire cab first, before you start disconnecting things and possibly changing the wiring configuration.
     
  15. bigbeefdog

    bigbeefdog Who let the dogs in?

    Jul 7, 2003
    Mandeville, LA
    Happened to have a caculator close at hand..... if this was done, the overall cab impedance would have been reduced to ~2.9 ohms, too low for the SVT 3.... indeed could have been the problem.

    If you find an 8-ohm replacement driver in there, the shop that repaired your cab is now responsible for the damage to your head. :meh:
     
  16. johnbegone

    johnbegone

    Sep 16, 2004
    Chicago, IL
    The new replacement driver is 32-ohm.

    What else can I check? I don't have a DC Resistance checker. How much and where can I get one?
     
  17. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    Any multimeter should do it. Mine was only $10 Australian (So About $8US) and I bought it from Radio Shack. Every musician should have one.
     
  18. Jerrold Tiers

    Jerrold Tiers

    Nov 14, 2003
    St Louis
    1) How long ago was the amp bought?
    2) Do you have your (or the original) sales slip?

    If the answers to 1 and 2 are "less than 5 years" and "yes", then don't mess with it, make us fix it under warranty. That is what the warranty is for, to protect you against problems.

    The amp is protected against the usual forms of abuse, but as with all things, stuff happens.

    No, we aren't going to complain about a shorted load voiding a warranty, if yours is still in force. The amp has protection which should take care of that, so.......

    I don't know what happened, but the unit drives 4 ohms fine. So that wouldn't be the issue in general. Fans going to max typically means over-temperature. Could be due to speaker. Might be that the amp just failed right then, and the speaker had nothing much to do with it except encouraging you to crank it.

    From what you said so far, you did nothing that wouldn't be "expected". You turned it off when it had a problem. You turned it on again later to see if the problem went away....reasonable things to do, although I might have unplugged the speaker at first, myself.

    Hopefully your warranty is still in force.

    As far as the speaker, there you need to look and see if any wires could have gotten crossed, fallen away from their intended connections, etc. Are any drivers stuck, or not freely moving, rubbing etc?

    If I had no test equipment, I'd try it with a battery...like a 9V, and see if it went "thump" with all drivers when I hooked up the battery briefly. That won't hurt the speaker (its bad for the battery, but whatever) and gives useful info. If they all move, and you don't see any wiring issues, very possible there is no problem at all.

    Yes there are 8 32 ohm speakers, all in parallel, in the Ampeg 8-10, so the wiring is particularly simple.

    Now, if someone wired in a 4 ohm driver, the total would be a bit over 2 ohms. Too low for the amp, but it still shouldn't have failed.
     
  19. johnbegone

    johnbegone

    Sep 16, 2004
    Chicago, IL
    The amp is about 13 years old, so any thoughts of warranty are out the door. For some reason I decided to plug it back in with the top off (this time I plugged in my 4x10 instead of the new cabinet). Right away it sparked up and had a tiny fire. This time I could actually see exactly where it was coming from, which was over by the power section. I took pictures.

    [​IMG]
    [​IMG]
     
  20. cb56

    cb56

    Jul 2, 2000
    Central Illinois
    If you need to borrow an amp to get through a gig let me know. I'm right down the road from you. Just don't plug it into that older cab until you get it checked out. :)