GK Fusion 550 Preamp Tube Problem???

Discussion in 'Amps [BG]' started by zot, Jan 5, 2014.


  1. zot

    zot

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    Hello all.
    I am in need of some help if anyone can provide it. My Gallien-Krueger Fusion 550 just isn't producing the power that I would assume that it should be. I bought it a few years ago from a music shop in Tennessee and got it home to Texas. It never produced very much volume...seemed really underpowered. I contacted GK but their rep told me that warranty starts at build date...not purchase date, so I was out of luck as far as warranty coverage was concerned. Not having the money to pay to have it checked out, it just started collecting dust until I could take it to and authorized GK repair shop....the nearest is 150 miles away. Unfortunately that still hasn't happened. At this point, I'm already out the money and still can't afford the shipping and labor costs...so I figured what the heck, I'm just going to try to do things myself.

    I took the lid off of it and started to check things out. The only thing that I noticed that seemed to be a bit peculiar to me was the middle 12AX7 preamp tube. The dual filaments of the two preamp tubes on either side both burn at a relatively even glow. The middle one has one side that is burning a lot brighter on one side...even compared to the other ones... and barely on the other. Could this be leading to the problem?

    I've added a photo, and it makes the filaments look a lot more even, but with the naked eye, the middle one almost looks like the one side isn't burning at all and the other one is much brighter. I know this isn't a great way of diagnosing things but I have to start somewhere. Can anybody help?
     

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  2. B-string

    B-string Gold Supporting Member

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    Warranty only starts on the build date if you don't have a sales receipt. Where is the gain set and the Woofer master? Do you have the switch set to active instead of passive. It takes a VERY hot active bass to overload that preamp.
    It is possible that center tube is defective as all tubes from the same maker should look pretty much the same. That glow is a heater the warms up the cathode inside the tube so it will "give off" electrons.
     
  3. zot

    zot

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    Hmmm....I had a receipt...Luis was the guy that emailed me back and told me that it was out of warranty due to build date. Never mentioned a thing about with or without receipt. Oh well...

    The gain was set at about the 1 o'clock position and the master at about the 3 o'clock position. The switch was set to passive using a passive bass. It starts to growl with the gain turned up higher but it just doesn't produce the volume that it should. It was basically set up like the "rock" sample setting in the owner's manual.
     
  4. Simon Langley

    Simon Langley

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    If it doesn't sound like it is putting out the amount of volume it should it probably isn't. These amps a foolishly loud and when I owned one (now a MB Fusion) I was always amazed at how low my volume settings were at gig volume. Barely even pushing it.

    First off, all of B-Strings questions might sound kind of dumb but are good ones and will help us help you. Something I'd like to add is a cheap and easy test for the tube is to swap it with one of the other two and see if anything changes. If the uneven glow follows that tube then it most likely is a bad tube. If the uneven glow stays in the middle position with a different tube that would indicate a problem with the amp. Also if the output level changes for better or worse when swapping tubes around you'll know it is the tube or tubes causing the problem. I had a ca strophic tube failure in my 550 once. I heard a loud pop and then no volume at all. If I remember correctly it was the middle tube that failed in mine as well. Hope this is the case for you as well and you are able to get up and running without much trouble.

    Last thing I'd like to offer is that if you do find it is a tube I have many extra new JJ preamp tubes (like they use in the 550) on hand and would be happy to send you one at no charge since it sounds like it might be tough for you to get your hands on one. When my tube failed the kind folks at GK sent me a brand new set of three at no charge even though a bad tube is definitely not their fault. Jason at GK is apparently very particular about the tubes they put in that preamp which, as I understand it, is why they come stock with premium JJ tubes. It's not much but it would be a way for me to pay forward what GK went out of their way to do for me. Also, I'd hate to see you give up on this amp as it is such a sweet sounding piece of gear. I'd still have mine but my aching back was begging me to go class D and I was losing the argument.
     
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  6. Simon Langley

    Simon Langley

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    Wow, gain at 1:00 and master at 3:00?!?!? That should have been loud as f$&k if you'll pardon the expression. Any buzzing, static or other unusual noises? Was the signal distorted or just low in volume?
     
  7. B-string

    B-string Gold Supporting Member

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    Your trouble may actually be the first tube on the left. That one is the first gain stage. At those settings even with an 8 ohm 212 it would be driving everyone from the room unless you have the volume low from your bass/bad battery in an active or shorted cable somewhere. The Fusion 550 is my gigging amp, unless I'm outside not in the PA I can get to 11:00 on the master.
     
  8. zot

    zot

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    Thanks so much Simon! I'll PM my address to you. No other unusual noise, just low volume. I figured it should have rattled the rafters at that point from all that I've heard. I've been afraid to push things too much so I didn't inadvertently cause more damage. I didn't want to give up on it either as I have heard so many good things about GK equipment. I really appreciate that you and B-String are trying to help me get to the bottom of this issue!!
     
  9. Simon Langley

    Simon Langley

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    No problem, let me know your findings after swapping the tubes around.
     
  10. zot

    zot

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    Thanks, B-String! I'll check that out and see what happens
     
  11. B-string

    B-string Gold Supporting Member

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    No trouble. Tubes are the easy things to swap and I can't see giving up my 550 unless both hands stop working and I couldn't learn to play with my feet. You need to experience it :)
     
  12. zot

    zot

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    Well, I swapped the tubes around with no real effect. The one tube is definitely burning differently than the other two. I'll see if replacing it helps and go from there. I'll keep you posted.
     
  13. elwuss

    elwuss

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    Simon, did your episode with the bad tube caused any damage to the amp?
     
  14. GretschBassist

    GretschBassist Banned

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    I suggest not to power up the amp until you have all tubes swapped for new ones. GK used JJ 12AX7 Tubes in this amp, they can be found here.

    I looks like one stage (remember this is a dual triode) of the one tube is malfunctioning but I find it easier to swap all the tubes at once so I won't have to remember when I put in which tube if that makes sense.

    The amp is supposed to put out enormous volume so this sure is a malfunction and your first start is always the tubes. Next would be checking the circuitry but that doesn't have to be done by a GK dealer, that has to be done by a good amp doctor because there is no special "GK magic" in it that no one else would understand. The schematics are actually painted on the amp, right? ;-)

    Keep us posted please, I'd like to see you happy with the amp as I think this is DAT amp really ;-)
     
  15. Simon Langley

    Simon Langley

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    No permanent damage. Popped new tubes in and away I went. Will try and get new tube out to you this week.
     
  16. godsey

    godsey

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    I bought one of those amps when they first came out and in about a month it did the same as yours,the dealer sent it back and ordered me another.never did find out what it was.
     
  17. elwuss

    elwuss

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    maybe a bad batch of tubes?
    mine works fine for the past year - rehearsals, tours, no problem whatsoever.
     
  18. bray101

    bray101 Supporting Member

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    When I first got mine, it had the exact same issue. I bought it used off of here and the seller had no reported issues with it so I knew it had to be tubes. I took the top off, powered it up, and the middle tube was the fault.

    I changed it for a Mesa 12ax7 that my guitarist had in his vht special 6 combo in his bedroom. When this worked, I just dropped a new set of JJs in there that I happened to have laying around and haven't had a single issue since.

    5 minute fix once I figured out the problem.

    This may sound extremely basic, but tubes are super sensitive. They have to be placed in those slots just right or they'll fault.

    Hopefully this helps. I'm actually in awe if you have the master at 3:00! I can't imagine the volume that would throw out if I did that to mine. Never had it past noon, and even then was solely to see how loud it was. I play with a loud guitarist with a Marshall JCM900 through a Marshall 412 and Orange 412 and I smoke him with my Fusion 550 and Neo 412 if I'm on 11:00. Can't imagine 3:00. Haha. Normal practice volume is only around 9:00 for me and that is crazy loud also. Please turn that master down once you change the tubes when first trying it out!

    If you're issue is just very faint output, almost fuzzy sounding, 9/10 it's the preamp tubes. Before I really knew anything about this stuff I had an ampeg SVT-3 Pro. Went to trade it at Guitar Center and the second I walked in there, this happened. Salesman plugged in and barely got anything. Sent me on my way and I overpaid some tech at a local ship to change a tube. Wish I knew then what I know now.

    Hopefully that free tube fixes you up!
     
  19. elwuss

    elwuss

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    same here!:D

    one of my guitar players has Marshall Superbass JMP with 4x12, the other has 2 Fender Twin reverbs with and extra 1x12, so 6x12 altogether.

    I play through Ampeg SVT 810E.

    Never go beyond 10 o'clock.
     
  20. bray101

    bray101 Supporting Member

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    Yea. Pure insane headroom on that.
     
  21. zot

    zot

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    Thanks for all of the help!!! :) I really hope that the simple fix does the trick. With my luck, I'm not going to hold my breath. Just saying that I'm disappointed with this whole thing is an understatement. I really stressed over what amp to get and after seeing all of the positive comments about GK. I thought I had made a wise decision. I'm still afraid that I might have a $1000.00 brick on my hands. I guess that's what I get for being a nice guy and not raising hell with GK over the warranty back then.
     

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