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Can mis-located phase inv. tube cause power tube to blow?

Discussion in 'Amp Central Station' started by stebon, Apr 25, 2004.

  1. stebon

    stebon Tele-Meister

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    I just unpacked a '65 Bassman head, AA864, installed the two power tubes and turned it on. In my excitement, I neglected to check the other tubes first and after noticing the second 6L6 was not lighting up or getting warm, I shut the amp off and checked other things. What I noticed was that the first tube after the power tubes was a 7025, not a 12AT7 as per the tube chart. The previous owner had a 12AX7 in the last position where a 7025 was supposed to be. Two questions, could this mis-location cause the second power tube to blow, and what is the difference, if any, between a 12AT7 and a 12AX7? Any input is greatly appreciated.
    Thanks in advance.
     
  2. Pierce

    Pierce Tele-Holic

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    7025 = 12ax7

    just a milatary number..

    switch power tubes around and see if it's a bad socket (the formerly lit tube doesn't light) or a bad tube..which still won't light up
     
  3. Dacious

    Dacious Poster Extraordinaire

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    No. Earlier Fenders used a 12AX7 for a phase inverter, as do Marshalls and Vox amps amongst others.

    The 12AX7 had more gain and many people like to sub them in to get more dirt, although SF and most BF Fenders are optimised for 12AT7s. If a tube is not warming up - a socket pin for heaters may be not making contact. Or the heater element in the tube may have broken in transit - perfectly possible.

    It sounds like the amp might need some attention.
     
  4. stebon

    stebon Tele-Meister

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    Thanks, that was fast! (e.o.m.)
     
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