Tube replacement for Fender Bassman 50

Discussion in 'Amps and Cabs [BG]' started by 8_finger, Oct 13, 2004.

  1. 8_finger

    8_finger Supporting Member

    Jun 1, 2002
    Baltimore, MD
    Two of the preamp tubes are dead. According to the shematics they're 7025/12AX7 if I understood it correctly. My question is: can I replace them with any 12AX7 tube?
    Are there different types 12AX7 tubes, and what types/brands should I avoid?
    Any info is greatly appreciated :)
  2. How did you determine that your amp's problem is the preamp tubes?
  3. 8_finger

    8_finger Supporting Member

    Jun 1, 2002
    Baltimore, MD
    Well there are 6 tubes in bassman 50 (from left to right):
    2 6L6
    3 7025/12AX7
    the last two of the 12Ax7's are dead - no glow in them :)
    I may be wrong, but tubes glow when they work :D
    Anyway I know I must buy replacement tubes for the two dead ones. And if there is another problem I'll take the amp to local tube amp repairman.
    But first I must know what tubes to buy
  4. Does the amp work? I noticed you don't mention any problem with it; you just asked about replacing "dead" tubes. Those two 12AX7's may be working just fine, but you may not be able to see the heater filament. That doesn't mean they're dead. They COULD have shorted heaters which WOULD render them useless, but not every tube has a filament you can see glowing, even when it is. Every tube type has a slightly different construction, depending on the manufacturer and there are SEVERAL examples of 12AX7's that have barely visible heater filaments.

    Have you tried playing though the amp? If the preamp tubes are dead, it won't hurt it to try to play through it; the amp just won't make much, if any, sound. If the amp works, you'll know the tubes are fine.
  5. 8_finger

    8_finger Supporting Member

    Jun 1, 2002
    Baltimore, MD
    The amp works just no sound coming out of it, actually almost no sound - it's barely hearable. The story with the amp is: this amp is in my band's practise room, the room is also rented to other bands and someone changed (well if you think about it - stole) the two premp tubes (which were almost new) with old, probably dead ones. The amp was working fine before that, so, I presume that it will work fine with new tubes. I'm taking the amp to local tech to check the amp anyway, but first I thought I'd buy replacement tubes.

    PBG thx for the help - I really appreciate it - I don't know much about tubes so I apologise for any annoying questions - I presumed that all tubes glow when they work because all other tubes in the amp glow exept th two 12AX7's
  6. 4Mal

    4Mal Supporting Member

    Jun 2, 2002
    Columbia River Gorge
    JJ's are really popular in the US for new. They are Chzech (?sp) made so they might be more available to you in Croatia. I run a JJ 12AX7 in my tube preamp and JJ 12ax7's and 12AT7's in one of my guitar amps. That one also uses JJ's EL34's. I look for those. Sovtek is a decent tube. I think the JJ's are 'sweeter' though.
  7. I second the recommendation for JJ 12AX7's. They're great and cheap.
  8. 8_finger

    8_finger Supporting Member

    Jun 1, 2002
    Baltimore, MD
    I'll check the JJ's then :)
    Thanks forr all the help
  9. Aaron Saunders

    Aaron Saunders

    Apr 27, 2002
    Sovtek tubes made a huge difference when one of the guys in the program bought some for his Bassman (he runs a Tele through it). There are even recoreded examples, and I've gotta say -- the Sovteks made a pretty muddy sounding distortion end up with a crystal clear crunch. Sounds fantastic now.