12AZ7 question

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by smolder, Oct 25, 2008.

  1. smolder

    smolder Gold Supporting Member

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    Anyone know how a 12AZ7A (GE NOS) differs from a 12AT7 or 12AX7?
     
  2. SatelliteAmps

    SatelliteAmps Member

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    Less gain. The gain factor of a 12AX7 is 100, and I think the 12AZ7 is 60.
     
  3. smolder

    smolder Gold Supporting Member

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    I did find out from another source that is is basically an 12AT7 (with similar gain) but that it has a better heater. Not sure how that would effect tone. My guess is that is will not sound significantly different than the T.
     
  4. wingwalker

    wingwalker Fuzzy Guitars

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    I use 12AZ7s' in place of 12AT7's in my vintage Twin Reverb...they are nearly the same as T7's...in truth I bet 98%+ poeple couldn't tell any difference
     
  5. clamdip7714

    clamdip7714 Guest

    I am using a GE 12AZ7 in my Phase Inverter and from what I have been told it uses a bit more current and is a bit slower warming up, otherwise gain is the same. I have a RCA and Raytheon as spares for later.

    I have to say it really added a ton of clean headroom to my amp. Jack "the builder" turned me on to it as an alternative to a 12AT7. The plus is people aren't asking for body parts in payment for them yet. ;)
     
  6. 59Vampire

    59Vampire Silver Supporting Member

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    wow I thought I knew about tubes. never heard of a az7. thanks for the schoolin!
     
  7. Gris

    Gris Member

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    The 12AZ7 is generally regarded as too microphonic for amplification use. Original use was for TV tuners. However, I am sure there are exceptions. I actually have a NOS one in my box. Never bothered to try it. Now I may give it a whirl in the old PI just for kicks and to test the microphonic theory. I wonder if mine is balanced...
     
  8. smolder

    smolder Gold Supporting Member

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    I popped my 12AZ7A (NOS GE) into V1 of my Dr Z Carmen Ghia and moved the 12AX7 into V2. I did an A/B with it and a (also NOS GE) 12AT7... both reduced the gain and added some brightness. The Z7A seemed slightly more defined... clearer (the opposite of muddy) to me. I know the (toneQuest guys) pros do this sort of thing for hours back and fourth and over a period of weeks... so YMMV... I spent about a half an hour.
     
  9. clamdip7714

    clamdip7714 Guest

    In a combo that might be an issue for sure. I have a head and I actually place some foam between the head and the cabs reducing any microphonic which could happen. I have a much better time now doing that, plus it extends the tube life. :)

    The AZ in the Phase Inverter sure seems to be the trick. I like the clarity and headroom. It had a 5751 in that position until now.
     
  10. nomadh

    nomadh Member

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    Can't believe I have'nt heard of this tube before. If you want more gain try the oddball 12bz7. Its a taller stacked gain ax7 it seems.
     
  11. rockon1

    rockon1 Member

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    I have a few and yes they tend to be too micro to use in any V1 spot at least. I have so many 12AX7's,5751, etc I just put them aside. Bob
     
  12. Steve Dallas

    Steve Dallas Supporting Member

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    I have several of these around here. I agree that they are too microphonic for most positions, but seem to do well in the PI position.
     
  13. Freepressright

    Freepressright Member

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    I used to think a tube being microphonic made it completely worthless for use in a guitar amplifier until I discovered high-temperature O-rings at my local hydraulics shop. I pay roughly a dollar a piece for them. Even the worst of microphonic tubes see a drastic improvement.

    I make sure I find a set that fits tightly and put two at each mica and one in the middle. Then install as normal. Guarantee you could probably make good use of a 12AZ7 in a guitar amp with a few of these O-rings.
     
  14. Timbre Wolf

    Timbre Wolf GoldMember Supporter Gold Supporting Member

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    Yes, that's true. Or you can use a microphonic tube as the phase-inverter, without the rings.

    - Thom
     
  15. frapat

    frapat Member

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    Can you show pictures of those O-rings and where do you put them ?thx
     
  16. smolder

    smolder Gold Supporting Member

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  17. Peteyvee

    Peteyvee Premium Platinum Member

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    You do realize that the post you quoted is almost 3 years old, right? ;) Just google "tube dampers" and you'll find out more than you ever wanted to know about the subject. Oh yeah, welcome to TGP!
     
  18. Mike9

    Mike9 Supporting Member

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    The red silicone dampers work wonders. They make tubes that might otherwise be thrown away useful.

    For a lark try a 12BZ7 - two 12AX7's in one bottle - Your PT needs to be up to snuff (enough current for another tube) In the right spot these are over the top -
     
  19. Ronsonic

    Ronsonic Member

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    I was going to mention that one. Fun tube in the right place.
     
  20. Scafeets

    Scafeets Silver Supporting Member

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    I've been using the red ones for a couple of years and they're great. If you buy 'em from a tube/music gear place they're about 2 bucks each. Get them from a local supply shop or http://www.oringwarehouse.com/ and they're about 15 cents each.

    EDIT: Looks like these guys went out of business. However, you can get them on Amazon now, among other places.
     
    Last edited: Mar 10, 2018
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