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Phase inverter, 12AT7 or 12AX7?

Discussion in 'Amp Central Station' started by JohnnyCrash, Jun 15, 2019.

  1. kbold

    kbold Friend of Leo's

    Jul 21, 2015
    I find all the GE JAN tubes to be consistently good, and still a good price compared to some of the cork-sniffing prestige NOS tubes (read as very expensive).
  2. 11 Gauge

    11 Gauge Doctor of Teleocity

    Mar 21, 2003
    Near BWI Int'l
    ...I guess it's getting off topic, but yeah, I have a similar thing going on - I've had a CMI Electronics 4X10 "SG" Gibson/Standel amp in my garage for at least two years now. My cousin gave it to me after fixing a bunch of gear for him. It has four alnico 10" speakers in decent shape. The preamp is all SS, and includes a Gibson Maestro phaser as a built in effect. The PI and power section are all tube, but the tubes are oddball 8417s - ~$150 a pair used - probably more than the value of the amp!

    Before he dropped it off, my cousin fired up some kind of Brit-sounding cab thru the SG's alnico 10s, just to show me how good they sounded. IDK if they are CTS are what, but yes, I've been tempted just to have that monstrosity serve as just a cab...

    ...But even if the thing isn't a collector's item, I've been reluctant to gut it, and put something all tube in there, in the 30W - 60W range. The PT will do 500VDC+ rectified, but there's no tap to really give the proper negative bias voltage. So the most straightforward thing to do would be cathode bias for 6L6s or maybe EL34s, but that seems kind of silly.

    I should probably just put aside the existing chassis and drop in something completely rolled from scratch, but I don't have much of either the time or desire to do that. So...the thing will sit in my garage for who knows how much longer.
    Greg_L likes this.
  3. zombiwoof

    zombiwoof Tele-Afflicted

    Oct 17, 2008
    Tujunga California
    My '65 Princeton Reverb that I've had since I was a kid has the circuit that calls for a 12AX7 in the PI position. I don't remember what circuit revision it is off hand (might be AA*65 or something like that), nor do I know if any of the other Fenders from that era had the AX7 PI tube. I have never tried anything but a 12AX7 in it, either.
  4. Commodore 64

    Commodore 64 Friend of Leo's

    Mar 1, 2010
    Kent, OH
  5. archetype

    archetype Fiend of Leo's

    Jun 4, 2005
    Williamsville NY
    Here ya go, folks. Tube Depot has NOS millitary 12AT7 tubes on ONE DAY sale 6/19/19. Philips @ $10 and GE @ $15. I grabbed a couple of Philips for my stash the last time they had them on sale.

    12AT7 and other NOS on sale
    Last edited: Jun 19, 2019
  6. Riffage

    Riffage NEW MEMBER!

    Apr 18, 2021
    Old thread but always relevant..
    Most amps react differently with various types, and most ears do too.
    Keep a nice variety of 12ax7's, 12at7's, and whatever power tubes you use on hand, so that you can perfect your sound. For the past week, I've been trying a variety in my peavey vtm 60. For the pi, I thought I'd settled on the ruby chinese 12at7 hg, but the at's ended up being a little bright and less ballsy than the ax7, which, In the end, for hard rock, my speakers, the mic and room; only enough, I found the sovtek 12ax7wb worked well. Never can tell..
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