Power tube falls out at high volume.

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by soniq7, Sep 20, 2008.

  1. soniq7

    soniq7 Member

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    Trippy. It just fell out and the sound verrrry slowly died. Never had this happen before. At first I didnt know what going on, and I kept upping the volume. Pretty soon there was no more sound :( , so I go round back to check the tubes and damn if theres not one missing!

    Opened the back of the 112 combo and sure enough, there lay the hapless 6L6. No damage. So I tightened up the buttfly retainers and put it back in.

    Have not turned it on yet, I was wondering if you fellas think its OK?
     
  2. oxydon

    oxydon Member

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    i started having the SAME problem today, and my very fine Sovtek amp sound really crappy now :s , i think one or two out of my four power tubes died, i hope it's not the same for you.
     
  3. SatelliteAmps

    SatelliteAmps Member

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    Tubes that fall might look ok, but not work when replaced. If that is all it is, you might just pop a fuse when you try to turn it on again.
     
  4. soniq7

    soniq7 Member

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    Its working, I got brave and fired it up.

    Thanks
     
  5. oxydon

    oxydon Member

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    good news, in my case the problem was with the speaker not the amp, i guess either the coil got a bit dettached from the cone and then when you turn the volume up it doesn't follow well, or maybe it's impedance mismatching, i got a no name speaker that says it is 8 Ohms but i think this is not precise at all, and i don't have a sufficiently precise multimeter to tell if it is really 8Ohm, can that cause problems at high volumes?
     
  6. FrankieSixxxgun

    FrankieSixxxgun Member

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    Vibrations and heat in combos can be a killer! 6L6s just seem to be suicidal too, I always hear of Fenders tossing their tubes.
     
  7. oxydon

    oxydon Member

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    it was not a combo, but a 100W head that gives to a poor no name speaker with medium size magnet and poor material, ... one could expect that xD.
    i open a subject on modifying cheap speakers to receive more watts and give more sound colouration.
     
  8. tim boehlert

    tim boehlert Member

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    Try re-tensioning the actual tube socket, and not so much the tube retainer. It's the socket itself that is loose. You could use a small dental-type tool to re-tension the individual pin holders - of course you need to discharge any voltages in the amp using the appropriate methods. This should take care of that problem, and then, yes, you can re-tension the tube base retainers - squeeze them in when the tube is out, then insert the tube.

    Fender's, and Boogies too as combos will always have problems with tubes slipping out of their sockets. Gravity works against you in this sense, and most of the 12AX7 style tubes, have no retainers, so your only option is to re-tension the sockets. I've been using my Boogies for about 30 years, and have only occasionally had to re-seat any tubes - a testament to their build, but that's not to say that the way I transport and handle my gear is anything like the way anyone else does it either. I'm very cautious, and transport way less now than I may have back in the 80's. But as a tech, that's always the first thing I check when setting up someone else's gear for a show - I can't tell you the number of 'guitar tech's' that I've worked with over the last five years that never had a clue about this or even checked. I distinctly remember one crew coming in, with some vintage style Fender's, and the guy simply fired it up without even checking for this common malady! When the amp is in STANDBY mode it's not much of a problem, and even when you turn the amp on to run, it won't be a problem UNTIL you start feeding it signal, then, yes, you can start to complicate the situation, and depending on the amp's architecture, you may increase your risk and cost to fix the problems.

    Re-tensioning these sockets takes a bit of finesse, and the right tools, and even some practice. ALWAYS discharge the amp - Gerald Weber has a great way to do this in one of his videos/books, which takes a minute or two, but fully discharges any dangerous voltages. Then simply remove the chassis form the cab, and get to re-tensioning! If you do it properly, it will take a bit more pressure to re-install the tubes, and then the base tension springs will do the job they were designed to do as well, without the extra effort required to compensate for the loose socket.
     
  9. tim boehlert

    tim boehlert Member

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    Measuring a speakers' impedance (AC) using a multimeter means that you're measuring DC resistance, NOT (AC)impedance - so expect an 8 ohm speaker to measure about 6 ohms (DC resistance), more or less...
     
  10. Nolatone Ampworks

    Nolatone Ampworks Silver Supporting Member

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    +1. Even if the tube clip is loose, a socket with reliable connections will have enough tension on the pins to hold it in.

    I recently worked on an old blackface Bassman head that had that problem. The tubes didn't fall out, but it would just cut out randomly.
     
  11. oxydon

    oxydon Member

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    Tim: yes i didn't know that, i always thought the 8 Ohm was the DC resistance given as an indication, but i think it's the impedance they measure at 1 Khz, the actuall DC resistance should be around 6 Ohm, my old analog multimeter is not accurate enough to measure such a small value, i think i should buy a digital one. thanks.
     
  12. rockon1

    rockon1 Member

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    My Rivera doesnt even have retainers on the power tubes. However the sockets have a "grip of death" hold on the tubes! Probably one of the only sockets I ever thought I might want to de-tension! At any rate +1 to re-tensioning the sockets. Bob
     
  13. Structo

    Structo Member

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    I have noticed on my amps that have the butterfly retainers that different brand tubes have different diameter bases.
    Some are smaller than the others and if you don't re-tension the retainer they could fall out.
    I think I would look into re-tensioning the socket pin connectors just to make sure they are making good contact.

    Then re-tension the butterflies and you should be good to go.

    Be careful when re-tensioning the socket connectors as they could have voltage on them from the filter caps.
     
  14. Structo

    Structo Member

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    And if you re-tension the pin connectors, it's a great time to use some DeOxit on the pins of the tube to clean the connectors.
     

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