amp messed up?

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by Prymo, May 17, 2005.

  1. Prymo

    Prymo Guest

    I recently noticed on my 2003 Dual Rectifier solo head that all the tubes were gloing on the amp when in standby, but when i switched standby off only 3 of the power tubes had that blue glow from the voltage hitting them.

    I thought the 1st tube was dead because of this. so i went and bought a quartet of tubes and retubed today. But the same thing is happening. Only 3 of the tubes are glowing blue from full voltage.

    Should i be worried about this, or am i freaking out about nothing?
    the tube jack in question is the 1st power tube on the near the output transformer.

    is there something wrong with the amp, a simple fix, or will if be costly.
    what do you guys think.

    btw the thing sounded great! im just worried that im not getting 100% of the power. and the ohmage will be messed up.
     
  2. John Phillips

    John Phillips Member

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    First, swap one of the tubes that does glow blue into that spot and see if it now glows, that will rule out the coincidence of getting another 'odd' tube in the new set of four.

    If the tube still doesn't glow blue in that spot, pull all the other power tubes and see if the amp works with just one in that socket - just at low volume, you don't have to run it for long to find out and it won't do any harm.

    If you get no sound, the socket isn't operating properly. The most likely reasons are a failed screen resistor, or the socket contacts being a bit loose and not making proper contact. Not a big fix either way, although you may need a tech if you aren't experienced at this sort of thing.

    Don't worry about harming the amp having run it with only three tubes operating (if in fact you have) - the mismatch isn't severe and won't have caused any problems.
     
  3. Prymo

    Prymo Guest

    hey thanks alot John. i will try those things and see if it will work with just 1 tube. i dont think its a big deal, it sounds great. i just noticed this a few days ago while i was fixing the power source it was plugged into(it was shorting out)
     
  4. Prymo

    Prymo Guest

    ok, i pulled the three other tubes out, and there was sound but it was very quiet and when i raised the volume it started cracking. so i moved that same tube to the socket next to it, it lighted up blue, and sounded normal no crackeling- huge difference form the frist try.
    so there must be something wrong with the tube socket.. its not loose cause i was getting some sound out of it. but sounded kinda like a short or something.

    there is no mesa dealer around here. should i bring it to a local tech?
     
  5. John Phillips

    John Phillips Member

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    Yes. It's bound to be something simple since it must be directly related to that socket alone - both of the sockets on that side are in parallel, so if it works with the tube in the other one, it can't be anything other than the socket itself, the screen-grid resistor (which are separate, one per tube), or a bad solder joint. Should be quick and cheap to fix.
     
  6. Prymo

    Prymo Guest

    ok, thanks alot John,
     
  7. mc5nrg

    mc5nrg Supporting Member

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    JP is a great asset to these boards.
     
  8. Prymo

    Prymo Guest

    hey John, good call. It was a screen resistor, i think this happend befor i got the amp because i got it used. but it almost melted right through the board.

    but its getting fixed now.
     

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