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My vintage Mullard 12ax7 is microphonic. Any hope?

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by skhan007, Feb 13, 2009.

  1. skhan007

    skhan007 Supporting Member

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    I noticed a high pitched constant squeal in my 1974x 18 watt amp and discovered the culprit was my vintage Mullard in V3. It's a shame because the tube sounds fantastic in that position otherwise. The squeal goes away when I turn the TMB channel volume down to about 11 O'Clock, but I like it at about 3 O'Clock for the music I play.

    The high pitched squeal is most noticeable when I'm not playing and very faint in the background when I am playing. I've just swapped in an old GE 12ax7 and an old RCA 7025 into V3 and the squeal is gone, so I know it's this Mullard. Any hope here or is this tube now trash?
     
  2. SatelliteAmps

    SatelliteAmps Member

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    You can get a tube damper to put on it and hope for the best.
     
  3. nitehawk55

    nitehawk55 Member

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    Iit may or may not help but try a rubber band wrapped around it a few times, they don't get hot like your power tubes . Good for a try before spending $$'s on rings .
     
    Last edited: Feb 13, 2009
  4. jcs

    jcs Member

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    try a few of the silicone rings like ted weber sells,it may or may not work..
     
  5. Timbre Wolf

    Timbre Wolf GoldMember Supporter Gold Supporting Member

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    Tube dampers do work, to an extent, in my experience. I use the "brass ring" that Brent Jesse sells, in more extreme cases. But the other redeeming use for a coveted microphonic tube is as a phase-inverter.

    - Thom
     
  6. jcs

    jcs Member

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    hey i've been tempted to try one of brent jesses' brass ring dampers.

    so they really help?
     
  7. fisheric

    fisheric Member

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    sometimes the tube can be used in another amplifier correct?

    some circuits only use 1 side of 1 12ax7? so if one side is microphonic the other side might be okay?
     
  8. Timbre Wolf

    Timbre Wolf GoldMember Supporter Gold Supporting Member

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    Yes - I've found them to be helpful. The only drawback is that if you take the damper off several times, it becomes kind of loose. You can fix that, a little, by straightening the "hairs" on the velcro-like stuff inside the damper.

    - T
     
  9. Timbre Wolf

    Timbre Wolf GoldMember Supporter Gold Supporting Member

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    Sure - take it out of a combo, and use it in a head (or a rack unit). That just reduces the vibration, but it does work.


    - T
     
  10. skhan007

    skhan007 Supporting Member

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    Thanks guys. You know, it is in a 2x12 combo that shakes a lot. But I've been using one of those aluminum sleeves on the outside (spring-loaded inside) and that didn't do anything for the microphoinics. Would a dampener be any different? I'll try it in my Marshall head and see if it works there.

    I like the idea of using it as a phase inverter too. Right now, my phase inverter tube is an old Amerpex Bugle Boy, which works great in that position. I'll do some swapping around and see what happens. Much appreciated!
     
  11. rockon1

    rockon1 Member

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    Got a faucet repair kit around the house? Usualy they have a bunch of rubber o rings ot even rubber grommets that will fit the tube and take the heat. Try about 4-5 on the tube. Bob
     
  12. Timbre Wolf

    Timbre Wolf GoldMember Supporter Gold Supporting Member

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    Well... make sure they're the kind that are circular in cross-section (nitrile), not the flat kind. True rubber will degrade and stink. Nitrile is heat-resistant, and wont make your practice pad even worse-smelling.

    - Thom
     
  13. 59Vampire

    59Vampire Silver Supporting Member

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    I was going to suggest the same thing. My 18 watt is VERY sensitive to microphonic tubes! Even one that is good in one amp will be bad in this amp. I sell parts of my stash from time to time when needing money and running the tube through the poisitons in the 18 are part of my QC!

    Good luck with the damper
     
  14. rockon1

    rockon1 Member

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    Faucet orings are fairly high temp-they have to be. Anyways Ive used them. BTW I make my living messing with orings-high temp and otherwise. Viton,silicone,nitrile.... Bob
     
  15. skhan007

    skhan007 Supporting Member

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    I swapped the microphonic Mullard into the phase inverter position and put the Amperex Bugle Boy where the Mullard was. Sounds good and no microphonics now. Not ideal, because I liked the Mullard in the position it was originally.

    With respect to the tube dampener idea- the goal is stop vibrations, but the mullard makes the high pitched noise even when I'm not playing. Not sure the dampeners would do anything- please chime if I'm wrong.
     
  16. Timbre Wolf

    Timbre Wolf GoldMember Supporter Gold Supporting Member

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    I just wanted to make sure nobody was using a cheap hose bib. That'd really stink!

    - T
     
  17. Timbre Wolf

    Timbre Wolf GoldMember Supporter Gold Supporting Member

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    It sounds as if that Mullard is microphonic. It can happen even with the slightest provocation (low-vibration). Did you try re-seating the Mullard back in its original position?

    - T
     
  18. rockon1

    rockon1 Member

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    Try it. Temporarily use a couple rubber bands on the tube. Bob
     
  19. fisheric

    fisheric Member

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    this will work on some tubes. what have you got to lose? a couple O-rings that you can use on another tube if they dont work, or your precious mullard.
     
  20. skhan007

    skhan007 Supporting Member

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    Yes, I put the Mullard back into V3, turned on the amp, and it was fine... Until I hit the first chord, then the high pitched constant squeal was back.

    Great idea. I'll find some and give this a try. I was going to go to Lowe's tomorrow anyway for other supplies, so I'll try to find some the O-rings mentioned by others as well.


    Definitely. I've got nothing to lose, so I'm going to listen to every bit of advice offered by you kind gentlemen and see what happens. I've only had this Mullard for about 2 months, so I'm bummed it's microphonic- but I'm not surprised because it was made in 1958 and has been used prior to my receiving it. The wife will be out of the house for a few hours tomorrow and I'll just be a really good father and put the kids in front of the TV and experiment with my tubes in the other room! I'll keep everyone posted on the progress.

    Another quick question (that could actually be a separate topic, but I'll ask any way since we're all talking vintage tubes here): I currently store all my tubes in the small cardboard boxes that some came in. Is there a tube storage case made by anybody that I should be aware of? Maybe something that'll allow me to inventory them in some fashion? Thanks again everyone.
     

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