retainer springs making tube microphonic?

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by spikeRI, Oct 3, 2005.

  1. spikeRI

    spikeRI Supporting Member

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    just got a Lightning clone in a trade. It sounds real good but has a problem when guitar volume is over 7........it starts this buzz that sounds like a bad speaker. Already tried a extension can with 2x12's and still does the same thing. I also replaced all tubes with proven tubes and inspected everthing fo make sure nothing was loose, burnt or obviously broken.
    I am able to get a reasonable amount of volume, but as soon as I turn up the guitar the problem comes back............I suspect the retaining springs on the el84's.......they are awful close to the tubes and to my thinking my be touching the tubes once the get cooking and vibrating a little.....
    anyone ever had a problem similiar to this?
     
  2. Wakarusa

    Wakarusa Member

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    If it does it thru the extension speaker (internal speaker disconnected, right?) then vibration is an unlikely cause. Do you get the buzz with the preamp turned up and the master volume turned down?
     
  3. Reeek

    Reeek Member

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    I just think you have a microphoic tube or tubes and I'd actually start by replacing the preamp tubes first. A combo environment is a brutal environment for vacuum tubes already then some combos are worse than others with respect to vibration.

    I once owned a Carvin Bel Air (4xEL84) and that thing just ate tubes left and right and most of the time, it was when it was turned up beyond 4 which is pretty loud. But sure enough, it vibrated like a cheap motel bed and much more than other combos I have. Just laying my hands on it while striking a chord proved to me that all combos are not created equal in this area.

    One thing I did learn though is that those combos that have a closed cell foam strip around the contact point between the chassis and the cabinet should not be tightened so tight that the foam is smashed tight. I learned that if I left some shock absobtion area in the foam, it wasn't as bad.

    Good luck!
     
  4. spikeRI

    spikeRI Supporting Member

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    microphonic tubes is what it sounds like............but, I replaced them with several sets.....too make sure. I did try tapping the tubes with a pencil and V1 had a slight ring to it (no matter which tube I tried in there)

    Todd, did not do much messing with the master.....I'll try tonite and yes the buzz was in the extension cab(internal dissconected) also (which made me rule out anything mechanical), but this idea about the retainers came from feeling vibrations even when hooked to the extension instead of the internal speaker...
     
  5. Wakarusa

    Wakarusa Member

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    The check with MV turned down is looking for problems in the preamp. A bad plate load, ferinstance, will create the nasty buzzing when you turn up the gain (tho sometimes the amp has to get good and warm before onset of the buzz in this situation). Could also be a bad coupling cap, though this is usually evidenced by a more intermittent buzz/shriek/crackle/howl.
     
  6. spikeRI

    spikeRI Supporting Member

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    appreciate the info and definately will fiddle around w/the MV to try to further isolate the problem....

    sounds like my retainer spring theory isn't going to hold, but worth asking about.....

    another bit of info I can give is this buzz starts right about where the amp starts flubbing (similiar to where a old fender flubs, which is typical of this amp(except the buzz part).......so I hear)
     
  7. Enzo

    Enzo Member

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    If you want to be scientific, just remove the retainer springs. If it still rattles, it ain't the springs.

    EL84s are notorious for rattling inside the tubes. Even new tubes will rattle. I like to rap on the side of the tube with my knuckle to test for inner looseness. if I can hear it rattle inside when I hit it with my knuckle, I can count on it rattling in the amp.

    Alternatively, have someone grasp the EL84s while you play in the way that makes the rattle. Use a rag or gloves if the tubes are too hot. If holding them stops the rattle, it is the tubes.

    This is a common problem.
     
  8. spikeRI

    spikeRI Supporting Member

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    turned the MV down as Todd suggested brought the volume up and it started fairly early.............not as bad with the volume level down, but you could hear something amiss.
    So, it off to the shop and let someone less dangerous than me do the troubleshooting.
    I will try enzo suggestions just for my sake, but doubt both pair of JJ's rattle...

    appreciate the suggestions....
     
  9. VacuumVoodoo

    VacuumVoodoo Member

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    Power transformer may vibrate if it is not properly tightened and firmly attached to the chassis. This vibration can cause retainer springs to vibrate against the tubes.

    Just one more probable cause.
     
  10. spikeRI

    spikeRI Supporting Member

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    gotta admit, didn't check...........tho I think it was tight (will recheck and thanks!!)
    a friend on another board suggested something might be amiss with V1 because it "rings" when tapped with a pencil
     
  11. Wakarusa

    Wakarusa Member

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    If V1 makes excessive noise when tapped (excessive is tough to describe) then it can certainly be contributing to the problem, but a microphonic tube usually won't wreak havoc when playing through an extension cab (as you tried earlier) -- decouples the vibrations.

    If you get the nasty buzz with the gain up, but the volume down (or, from the point of view of the controls, volume up, master volume down), and you've replaced all of the tubes with known good ones, then it's time to start looking for marginal plate load resistors and leaking coupling caps in the preamp. I think your decision to visit a tech is the right move.
     
  12. spikeRI

    spikeRI Supporting Member

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    yea, I can do a few things with amps, but only with guidance........I'm just smart enough to know when and where I should stick my fingers without getting lit up or destroying my amps.
    Its still worth trying the obvious first before going to the tech. Every once in awhile you can get lucky and the problem is something EZ.....
    While I'm getting it fixed, I'm going to have one of the caps(something that was discussed on the Trinity Lightning BB) changed which supposedly will cure the flubbiness in the bass...

    Thanks for all the help, I'll post the results when I get it back
     

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