Fender Blues Jr NOS and a Tungsol 12ax7

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by Rai, Feb 7, 2015.

  1. Rai

    Rai Member

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    I apologize for the noobiness.
    I just bought a new BJ NOS. All stock and I haven't done any mods (I don't know how and what).
    I also have 1 unused new production Tung Sol 12ax7 lying around here.
    Can i swap this with one of the groove tubes of the bj or does an amp always have to have the same kind of preamp tubes? If i can swap it, which one where i can have a higher headroom?
    Thanks in advance.
     
  2. Rai

    Rai Member

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    Or can that change only when you change the type of tube (not the brand)?
     
  3. Dan40

    Dan40 Supporting Member

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    Any of the 12ax7 preamp tubes can be swapped with any other brand of 12ax7 tube. Which brand sounds best and in what position is totally up to your ears and your taste. V1 is usually the spot with the most influence and the phase inverter can also make a difference.
     
  4. Rai

    Rai Member

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    Thanks. I'll go try it.
     
  5. swampbillly

    swampbillly Member

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  6. Stratobuc

    Stratobuc Member

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    Any 12--7 tube can be swapped for a 12AX7. The gain factor is higher with a 12AX7, and goes down from there. A lower gain pre-amp tube may give you more perceived headroom. A 15 watt amp will not have a lot of headroom anyway.

    [​IMG]
     
  7. kbgear

    kbgear Member

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    That's not strictly true; there are circuits designed around the higher plate current variants that could cause the lower plate current variant tubes to fail, and transformers that were not specced for the higher heater current variants and could thus fail. The former is more likely than the latter is far as I can tell, but it's not a simple yes or no.

    In this case, yes, V1 in a BJIII sounds best to me with an RCA, Tung Sol RI, or JJ ECC803s in that order. Only one of the triodes in V2 is used, so it doesn't have a big impact. I'd keep the V3 as-is, or maybe an 803s -- the Tung Sol RI IME made an already bright amp a little too detailed. I don't find the BJIII to be too gainy, but a 5751 might be a good choice for V1.

    YMMV etc, but short of the long is "sure, V1 is your best bet". ;-)
     
  8. Rai

    Rai Member

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    Thanks for all the great info and links! Read billm's articles on his site. Hope he is ok. Gonna do that wire dress tip. The rest I can't touch as it might void the warranty.

    So i put the Tung Sol in V1. Does not sound any different in my apartment but i'll know (hopefully) when i turn it up at band practice. Thanks again!!
     
  9. kbgear

    kbgear Member

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    Yeah, it's pretty subtle, though less so for all the tube-rollers out there. ;)

    I'd expect a different midrange and a but more treble and definition. That being said, I have experience with a BJIII with a Cannabis Rex, which just goes to show that you should always use what sounds best to you and not stuff that anyones says is the best. :)
     
  10. ylo

    ylo Member

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    FWIW, I have read on TGP that the Tungsol reissue and similar LPS 12AX7 tubes do not last long in the PI position. You might want to do a search here for more info on this.
     
  11. kbgear

    kbgear Member

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    Hmm, the LPS is a hugely popular PI. Maybe you're thinking of the Tung Sol RI in a cathode-follower position, which the BJIII doesn't have.
     

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