Main tubes or preamp tubes?

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by cr8z4life, Mar 28, 2005.


  1. cr8z4life

    cr8z4life Silver Supporting Member

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    I replaced my eh 6L6's with Sed's c logo's in my Top Hat Super Deluxe. and loved the change....played it wide open for an hour or two on friday.....played it today the same for maybe 15 minutes and then there was rattling....sounded like metal on metal.... just loud rattling sound.....obviously the tubes but which ones.....I would bet one of the Sed's are bad but figured I would check with you guys......
     
  2. Blue Strat

    Blue Strat Member

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    There's a very scientific way to find out.....put the EH 6L6s back in and see what happens. Even the most experienced tech with the amp sitting in front of him would use this method. There's very little magic in troubleshooting amps.
     
  3. cr8z4life

    cr8z4life Silver Supporting Member

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    Guess that would be the easiest, wouldnt it! Just figured I would ask....I cant see how the preamps could make a rattling sound that loud.
     
  4. Reeek

    Reeek Member

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    Oh, but the preamp tubes can indeed make a huge ruckus. What Mike suggested is just the first and easiest thing to try first. Certainly, if the noise is still present after the original power bottles are installed, you'll then be working through the preamp tubes to isolate the culprit(s).
     
  5. WailinGuy

    WailinGuy Member

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    Take a chopstick or a pen and tap each tube. If one of them is badly microphonic, it will announce itself when you tap it.
     
  6. cr8z4life

    cr8z4life Silver Supporting Member

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    I tapped the bottom of the 6l6's while they were in the amp with my finger....one - nothing....the other kinda made a rattle.....thats why I figure its the main tubes
     
  7. Blue Strat

    Blue Strat Member

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    Lots of good tubes will make some noise when tapped. You can try swapping in one of the EHs for the one SED tube and see if that calms things down.
     
  8. cr8z4life

    cr8z4life Silver Supporting Member

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    I will actually try taking them out this weekend and putting the EH's back in....if it doesnt do it....the sed's are going back for new ones.....if it does,,,, time to change the preamp tubes.......by the way....forgot to mention a bit of a burning smell....didnt think anything of it because I just figured it might be the new tubes burning in...
     
  9. Blue Strat

    Blue Strat Member

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    Yep, "tube scent" for the first few hours is normal with new power tubes.

    BTW, if that's a fixed bias amp, did you rebias? You must or you risk destroying the tubes, damaging the amp, or possible rattles or bad tone.
     
  10. cr8z4life

    cr8z4life Silver Supporting Member

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    i shouldnt need to....the Top Hat super can change between 6L6's and el 34's without bias so why would I need to bias it to change 6l6's?
     
  11. Blue Strat

    Blue Strat Member

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    Hence my question about whether or not it's a fixed bias amp.

    Also note that "self biasing" amps don't self bias under all conditions. In fact, a self biasing amp that "can run both el34s and 6L6s" typically runs 6L6s way too hot.
     
  12. cr8z4life

    cr8z4life Silver Supporting Member

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    Well, got it from the horses mouth (Brian at Top Hat) As long as the tubes are well matched- no Bias needed
     
  13. bigroy

    bigroy Member

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    This post is timely for me.

    I bought a used TopHat Club Deluxe last week, played it at a jam session. Loved it. Sounded great. Took it to a rehearsal for a pit band gig two nights ago, and got kind of a crackling static when I would dig in really hard on a note, or when I kicked in a OD pedal. I'm guessing it's a preamp tube, so tonight I have the chopstick method, with a little swapping of tubes. Most of the noises that I have self diagnosed successfully have been preamp tubes. I'll post a follow-up later tonight or tomorrow.

    I would start with the #1 preamp tube, the one closest to the input.
     

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