What tube for Phase Inverter?

Discussion in 'Glowing Bottle Tube Amp Forum' started by guitar0621, Mar 16, 2018.

  1. Rick330man

    Rick330man Tele-Afflicted

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    In amps that call for a 12AX7 in the PI, my experience is that the 1980s era GE 5751s will improve your tone. They always seem to give amps a little better detail and definition. I can't tell you why, but I can tell you that my ears consistently hear the difference in amp after amp.
     
  2. BillG

    BillG NEW MEMBER!

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    I like the way my Monoprice 15 watt sounds with a JJ 5751 in the phase inverter slot. I have JJ power tubes in it, but the other tubes are stock. Right now in the PI (v3) I have a JJ 12ax7 short plate and I don't like it. The Chinese tube sounded better. I'm thinking about getting a mid gain JJ and a Sovtek LPS to see which sounds better, those and a 12at7.

    In this particular amp whatever you have in the PI slot has a pretty dramatic influence on the sound you get. I tried the 5751 in both v1 and v3. It tames the gain in either slot. It's missing something though I think, especially in v1. I do think I want a lower gain tube in that v3 and maybe V1 too. You have more control and can get some great sounds out of this amp I think with a lower gain tube in the PI slot. It's like the gain knob is less sensitive and it's a slower transition from a good gritty sound to way more overdrive than I want.

    The Chinese tubes that came in my amp are high gain. In v2 and v3 it came with tubes marked China 12ax7b. The "b" is higher gain than the one marked "a" I've read. V1 has an unmarked tube with a smaller plate. Stock it didn't have much clean headroom and it seemed like there wasn't much of a range of overdrive/distortion that I liked. I'm not into heavy metal or anything like that though. I'm on an es-335 and like cleaner tones. I could still get plenty of distortion with the 5571 in the PI when I cranked the gain way up.

    If you have the Monoprice 15 watt amp, don't believe people who tell you a lower gain tube in the PI won't affect your tone. They're just plain wrong. Maybe it works differently on amps with different circuitry, but on this one the tube in v3 can make a big difference in the sounds coming out of the speaker. Try different tubes there. It's like you're playing through a different amp.
     
  3. v__k

    v__k TDPRI Member

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    I threw 5751s in my 15w Monoprice amp into both V1 and V3. I'm liking it so far.
     
  4. BillG

    BillG NEW MEMBER!

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    Did you try a 5751 in just one of those slots and if so was there much difference putting them in both?
     
  5. v__k

    v__k TDPRI Member

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    I replaced V1 and V3 at the same time, I didn't really take the time to replace one at a time to see what the differences were.

    Overall it seems a bit smoother and breakup happens later on the gain knob for me.
     
  6. FerruleCat

    FerruleCat Tele-Holic

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    I haven't seen references to this being a problem, but this is enough to give me pause. Have people run into this issue? (Also, I'm considering this tube for V1, not for the PI, if that makes any difference.)

    Thanks!
     
  7. VintageSG

    VintageSG Friend of Leo's Ad Free Member

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    It may have been an isolated case. I tried a 12AT7 as PI in my Cub, and phut! went the internal fuse. The draw was -just- over the blow rating of the fuse ( when measured ).
    Undeterred, I replaced the fuse and phut!.
    Undeterred, I replaced the fuse with the next highest value I had knocking about. As a PI valve, I felt it gave less distortion. It was a nice enough sound, if a little sterile ( remembering sounds and trying to describe them?, not my forte ), but it did give some girth to the sound when pushed toward the upper end of the volume and gain knobs. It stayed cleaner slightly longer was the main thing I remember.

    I tried it in V1, and like every amp I've tried a 12AT7 in the first signal position, it was a flaccid, uninspiring mess. Dull, matted to a non-reflective finish.
    What my ears hear and my grey lumpen spludge interprets is highly unlikely to coincide with your hearing and experience.
    Try it.
     
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  8. Silverface

    Silverface Poster Extraordinaire Ad Free Member

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    "Balanced" preamp tubes only work as "balanced" in a amp where the driver itself is carefully balanced - and most aren't.

    Most players seem to like a fairly well balanced driver tube, so a badly unbalanced 12AX7, 12AT7 etc probably won't please you, and a 12DW7 isn't suitable.

    Beyond that you can experiment IF the amp can handle the higher current needs of a 12AT7, for example. Not all amps that come stock with a 12AX7 driver can handle a 12AT7, so random tube swaps can be a bad idea unless you know what you're doing.
     
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