12ax7 in old Bassman

Discussion in 'Amps and Cabs' started by moss, Dec 6, 2016.

  1. moss

    moss Member

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    Is there any danger in running 3 12ax7 in a fender bassman 5e6.
     
  2. Humble Texan Fan

    Humble Texan Fan Member

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    Not if it has noval sockets for them. You may not like the sound of them, though, and they may not electrically perform their best but I couldn't see any harm coming to the amp as such.
     
  3. bob-i

    bob-i Member

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    Why would they not perform electrically at their best? This amp uses the same values for Rp, Rk and Ck as a super reverb.

    I've done this, and it just seems like a tad too much for what that amp should sound like.
     
  4. kimock

    kimock Member

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    You mean 12AX7 instead of 12AT7 for V3, right?
    Some guys prefer it, I'm fine with the AT personally.
    Can't imagine how it'd be a problem.
     
  5. Steppin' Wolfe

    Steppin' Wolfe Member

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    Using a 12AX7 in the input stage will up the gain throughout the signal chain....Marshall did it when they cloned the 5F6A. IF you like it, use it. One aspect of the second stage there is the cathode follower voltage. The AY has a max spec heater to cathode voltage limit of 90vdc. There may well be more than that on that tube. For the 5F6A, the schematic shows 180vdc on that cathode, and Fender went to a 12AX7 in that amp. The 12AX7 has a limit 180vdc on the heater to cathode. The 12AY7 has a gain factor of 40, the AX has a gain factor of 100. IF a person wanted to keep the gain lower in the second stage and yet felt that some accommodation be made IF the voltage on that cathode follower was high, one could run a 12AZ7, which has again of 60 and a heater-to-cathode limit of 200vdc.
     
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  6. moss

    moss Member

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  7. bob-i

    bob-i Member

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    Actually in that amp v1-2 are 12AY7 and v3 is 12AX7
     
  8. bob-i

    bob-i Member

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    The 5e6 shows 130v on the cathode of the CF. should be a problem for an ax7.

    The gain factor is a biggie though, but the tube should run fine.
     
  9. moss

    moss Member

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    No it calls for 12ay7 in v1 and v2
     
  10. kimock

    kimock Member

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    Cool! I must have been thinking of the wrong amp.
    I'd have to think swapping out a pair of 12AY's for a pair of 12AX's would be a more dramatic diff than my previous "wrong amp" comments.
     
  11. moss

    moss Member

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    Sorry I had to step out. Is it ok if i like it ? The amp sounds good with 12ay7 in V1 but will not break up at all. 12ax7 in V1 gives me some break up. But I don't want to fry anything.
     
  12. mad dog

    mad dog Silver Supporting Member

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    Mine is not an old one, but is a really good sounding replica. Sounds best to me with 12ay7 in V1, 12ax7 in V2, I think a 12ax7 in V3 also. I tried 12ax7 in V1 ... got a little too wild too quickly, earlier break up.
    MD
     
  13. woof*

    woof* Member

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    It wont hurt your amp
     
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  14. moss

    moss Member

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    Yes mine was restored buy Clark and that's how he shipped it. after about a year I got curious and stuck a 12ax7 in the V1 spot yesterday and was surprised at the difference it made. Was actually only looking for a little breakup as the amp can be cranked with no breakup in site. Do you jumper the channels with a y cord ?
     
  15. Steppin' Wolfe

    Steppin' Wolfe Member

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    Moss, you can try a 5751 in V1 for a gain factor in between the 12AY7,with a gain of 40, and the 12AX7, with a gain of 100. the 5751 has a gain factor of 70 and is designed to be a tone processing tube along with the AX and Ay. As noted above, you will do no harm.
     
  16. Steppin' Wolfe

    Steppin' Wolfe Member

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    The gain thing is the reason I mentioned the 12AZ7 for V2. IT has the heater to cathode voltage covered and is not as high gain as the AX.
     
  17. moss

    moss Member

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    thanks I will give it a try
     

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