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6550's in Mesa Bass 400

Discussion in 'Amps and Cabs [BG]' started by tombowlus, Jul 11, 2005.


  1. tombowlus

    tombowlus If it sounds good, it is good Gold Supporting Member

    Apr 3, 2003
    North central Ohio
    Editor-in-Chief, Bass Gear Magazine
    I just received my Bass 400 from ebay (in near mint shape, and with a cherry SUS-4 rack!), and it also came with the original operating instructions. Under "Power Tubes" it states:

    "The Bass 400 uses special Mesa STR 418 type 6550 power tubes... Do not replace these tubes with the larger metal base type 6550 such as Groove Tubes sell! First, they will not propertly fit into the hold down clamps; second, they are considerably more expensive; third and most important, they will fail constantly in normal use... Amplifier bias has been permanently set by us and should never need adjustment."

    On the schematic, it states:

    "V5-V10 use Mesa Type STR 418 6550 or 6L6."

    The amp came with 6L6's (STR 430), and the previous (and original) owner had also used STR 420's (also 6L6's). I'd like to run 6550's, but I am wondering what this "large metal base style 6550" bit is all about. Does anyone have any suggestions as to particular 6550's which would work well in a Mesa 400? Also, can the bias really be set such that it works well for both 6L6's and 6550's?

    Any comments or help are appreciated.

    Tom.
     
  2. The 0x

    The 0x

    Aug 24, 2003
    Timonium, MD
    It's Mesa's way of saying "buy our overpriced tubes that will only last a year so you can buy more of our overpriced tubes later."


    Get bias pots installed on there so you can use any brand of 6550s or KT88s in that sucka.
     
  3. tombowlus

    tombowlus If it sounds good, it is good Gold Supporting Member

    Apr 3, 2003
    North central Ohio
    Editor-in-Chief, Bass Gear Magazine
    Does that mean that I cannot use any other 6550's now? I know in my Strategy 400 (which is designed to run all 6L6's, except for 4 of the sockets, with will also accept EL34's), I had a choice of several 6L6's which were "close enough" to the Mesa "brand" to work without a bias control mod.

    Is it possible to find 6550's which are "close enough" to the Mesa STR 418's?

    Tom.
     
  4. Chef

    Chef Moderator Staff Member Supporting Member

    May 23, 2004
    Columbia MO
    Staff Reviewer; Bass Gear Magazine
    PBG?
    Bob at Eurotubes might have info for you...
     
  5. BurningSkies

    BurningSkies CRAZY BALDHEAD

    Feb 20, 2005
    Seweracuse, NY
    Theoretically, if you're running 6 x 6L6, aren't you only getting about 150 or so watts?

    I thought each of these tube types also had a different number of pins.
     
  6. tombowlus

    tombowlus If it sounds good, it is good Gold Supporting Member

    Apr 3, 2003
    North central Ohio
    Editor-in-Chief, Bass Gear Magazine
    Yeah, I was hoping to hear from Psycho, as his advice is consistently excellent. But, I can alway talk to Bob, or Christian, or Doug...
     
  7. tombowlus

    tombowlus If it sounds good, it is good Gold Supporting Member

    Apr 3, 2003
    North central Ohio
    Editor-in-Chief, Bass Gear Magazine
    Yes, that's why I'm interested in switching to 6550's (@ 300w).

    The pin configuration appears to be compatible.
     
  8. Hounddog

    Hounddog

    Dec 2, 2004
    Southern, Illinois
    Sadowsky Featured Artist
    Tom,

    Does the Mesa 400+ live up to your expectations ? I hope so I am gonna get me one this week.

    Mike
     
  9. tombowlus

    tombowlus If it sounds good, it is good Gold Supporting Member

    Apr 3, 2003
    North central Ohio
    Editor-in-Chief, Bass Gear Magazine
    Mine is the 400, not 400+, and I just got in via FedEx today, so I have not had a chance to fire it up. I've played a 400+ in a store, though, and it does the "tube head thing" very well!

    More to come, for sure!

    Tom.
     
  10. Here's what Psycho wrote in a previous post:

    I guess that doesn't address swapping 6L6s for 6550s, but note the reference to the power supply. Best to wait until he chimes in.

    Hope that helps, Tom.
     
  11. I always preffered the Ampeg SVT, I believe it is because of the tubes.
     
  12. Chef

    Chef Moderator Staff Member Supporting Member

    May 23, 2004
    Columbia MO
    Staff Reviewer; Bass Gear Magazine
    "Thread Swerve"

    Hound Dog, you buying one of thsoe from GC?




     
  13. Lebowski

    Lebowski

    Jul 11, 2005
    So by going with the 6550's, you get more "power" out of the 400+ than with the 6L6's? How does that work?
     
  14. BurningSkies

    BurningSkies CRAZY BALDHEAD

    Feb 20, 2005
    Seweracuse, NY
    Assuming the transformers can take it (and I'm sure they can, as I believe it's designed for 6550's more than 6L6's), a 6L6 can really only output 25w per tube in the best of conditions...while a 6550 produces twice that, doubling the power.
     
  15. tombowlus

    tombowlus If it sounds good, it is good Gold Supporting Member

    Apr 3, 2003
    North central Ohio
    Editor-in-Chief, Bass Gear Magazine
    Keep in mind, this is only an option with the Bass 400, not with the 400+! Do not try this with a 400+!!!
     
  16. Lebowski

    Lebowski

    Jul 11, 2005
    ??? Too many tubes?
     
  17. This is a 400, but yes, the 6550s produce more power. I believe that a 6550 is capable of about 50W or so. A 6L6 gives about 25W. The old 400 took 6 tubes, so it would give about 300W with 6550s. The newer 400+ gives about 300W with 12 6L6s.
     
  18. Awwww!!! But come on! 600W! :D
     
  19. The irony of this is that Mesa was being honest. At the time they made the Bass 400, it came with either Philips 6550A's or 7581's, both excellent tubes. (The 7581 is the latter-day TRUE STR 6L6GC.) At the time Groove tubes was selling junk Chinese 6550C's and touting them as equivalent to old American 6550A's, which is not even a funny joke. The ironic element is that after Mesa exhausted their supply of real Philips 6550A's, they started selling the SAME junk Chinese 6550's and assigned them an "STR" number to make them appear as though they were real STR tubes (which of course, they are not).

    Unless the amp uses "beartrap/ butterfly" tube clamps, the base size makes no difference. The other thing to remember, but it's a HUGE thing, is that sometimes the screen
    grid is tied to the metal base ground connection in SOME 6550A's. If you grab the base while the amp is running, you'll get a few hundred volts of DC through you.

    ANY decent ones should work.

    Nope; Mesa was full of it.

    BTW, the pinout of 6L6GC's is identical to 6550A's.
     
  20. Lebowski

    Lebowski

    Jul 11, 2005
    If the 6550's are not an option for the 400+, then are there any tubes better than mesa's 6l6's? i.e. higher watt output?