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Increasing Wattage on Fender Bassman?

Discussion in 'Amps and Cabs [BG]' started by BassGreaser, Jul 10, 2005.


  1. BassGreaser

    BassGreaser

    Aug 22, 2002
    Austin, TX
    I have a 70's Bassman 135 that is around 100watts with 4 6L6's. My question is...Is there an way to bump the wattage closer to 200watts by possible putting in 6550's? If so, what else would I have to mod? I ask because I love this amp, and the straight raw tone I get from it. I know the tone will change some what, but I can deal with it :D
     
  2. short answer....no. That's be ridiculously hard and expensive to do (have to replace all the trannies etc.) Btw.. the route to go is 4 KT88's.

    Cheers,

    Nish
     
  3. 4Mal

    4Mal Supporting Member

    Jun 2, 2002
    Columbia River Gorge
    More efficient cab's is the answer ...
     
  4. DaveMcLain

    DaveMcLain

    Jun 19, 2005
    Cuba MO
    You could take your 135 Watt Bassman and run it into a THD Hotplate or some similar attentuator. Then take the line level signal and use it to run a much larger amp, say a 1200 watt solid state power amp into the cab of your choice. Now you've got the tone you like but it's MUCH MORE POWERFUL!
     
  5. BassGreaser

    BassGreaser

    Aug 22, 2002
    Austin, TX
    hmmmmm....what should I expect if I just dropped in the 6550's with changing out the trannies, and everything else
     
  6. The 0x

    The 0x

    Aug 24, 2003
    Timonium, MD

    You can't do that. 6L6s have 6 pins, whereas 6550s have 7 pins.
     
  7. DaveMcLain

    DaveMcLain

    Jun 19, 2005
    Cuba MO
    You could modify the amp to use a 6550 without too much trouble and it would probably work ok. I think you would find that the amp might have slightly more headroom and a different tone with a different midrange. The problem I see with the swap would be the fact that the 6550 heater draws much more current than a 6L6 heater, I don't know if the Fender transformer can handle the additional load. Rewiring the tube sockets and adjusting the bias supply for the 6550 would be pretty easy. If you're experiementing with different tube types I think I would try a KT66HP from Groove Tubes. Their version is made in Russia and it will handle the over 500 volt B+ of your amp. It's a 6L6 style tube with a similar bias point, same pinout etc. It's got a HUGE bottle size and that might be a problem. We've been using them in Marshalls instead of the EL34's and they sound great..... It would be an easy swap if they will fit in the cabinet, be sure to get the made in Russia Groove Tubes version, not the Chineese for an amp with more than 450 volts B+..
     
  8. This is you putting the tubes in straight up:

    The tubes are too big (size wise)
    The amp will overheat and melt (the fact that you're pumping an extra 100W through a transformer incapable of handling it).
    You will blow the fuse because it is not rated for the right amperage.
    You will blow the power transformer as it can't handle that kinda current.
    You will get a massive change in sound as the rectifier sags...constantly.
    You will have next to no b+ so your amp running the plates insanely cold.
    You'll probably melt some blow some of the non cement resistors in the power section.
    If you replace the power transformer, you have to replace:
    -The rectifier
    -The caps
    -Resistors in power section
    -Biasing resistors
    -Power section
    -All the preamp biasing resistors

    DO NOT DO STUPID THINGS LIKE THIS TO YOUR AMP.

    The smartest option has been mentioned above. Either buy a hotplate or Weber Mass attenuator, and use the line out to power another amp or get an isolation cab and amplify the miked signal.

    http://www.randallamplifiers.com/products/cabinets/isolation/index.asp

    No wonder I get so many hopeless amp's at my repair shop... :rollno:

    Nish

    Edit: This is all if you use the KT88's as I recommended as the only 200w soloution. If you're running the 6550's you'll experiance all of these if you dime the amp. You might be able to pull the 6550's off...but the amp would become very distorted, and not like a bassman at all. But even for the 6550's you hafta take it to a qualified amp tech to have it rebiased, and some components changed to allow you to put in those tubes.
     
  9. BassGreaser

    BassGreaser

    Aug 22, 2002
    Austin, TX
    I fully agree with taking the amp to a tech. I was planning (if I do this mod) have Jeff over at Jeff's Guitars do all the work, as he designs his own custom guitar head, and combos. As for tubes. I think I would go with 6550's, but before I decide to do this. I will talk with Jeff to see what he says.
     
  10. I'd say to sell it and buy another amp instead of modding it. If you change the tubes, you just won't get that same bassman tone at all. Either sell it, mike it, or do one of the other options I mentioned above if you still want that same tone but louder. If you don't mind a rather large tone change, go for the 6550's.

    Cheers,

    Nish
     
  11. I personally wouldn't do it, but it's not as hard as some people have made it out to be. 6L6's and 6550's have the same pinout, so rewiring the sockets is unnecessary. You don't need to replace the power transformer entirely, just add a separate filament tranny for the 6550's. The lessened strain will make the whole power transformer run significantly cooler and supply higher voltage peaks for the power tubes' plates and screens. You'll still only get 170 watts max IF you significantly upgrade the power supply, but the feel and headroom of the amp will change considerably. Think of it as a sorta Mesa D180.
     
  12. DUH!!! Ever hear of a drill? Just drill another hole in the tube sockets.

    Never ceases to amaze me the crackpot advice people give on the board.... :eek: :bag: :D

    Randy
     
  13. BassGreaser

    BassGreaser

    Aug 22, 2002
    Austin, TX
    excuse my ignorance...what is the power supply. :crying:
     
  14. Power supply = power transformer, rectifier diodes, and filter capacitors. When I say "upgrade" I am referring to the filter cap bank. The PT and rectifiers shouldn't need it.
     
  15. BassGreaser

    BassGreaser

    Aug 22, 2002
    Austin, TX
    Psycho may i ask why you wouldn't do this mod other than the fact that it is a Bassman amp?
     
  16. The fact that's it's a Bassman has little to do with with it. Bassman 135's are 'pariah' amps in the vintage community since they're all "Silverface" and are primarily clean sounding due to having ultralinear output topology. I wouldn't mod it because it's a serious modification and even an experienced tech can easily screw it up. For the amount of money you'll spend to mod the amp that way, you could almost buy a new Traynor YBA200.
     
  17. BassGreaser

    BassGreaser

    Aug 22, 2002
    Austin, TX
    very true.I will have to think about this.....
     

  18. :rollno: octal sockets already have 8 holes....

    As an amp tech myself..I'd say it's not worth it at all. That's the loudest bassman you'll ever find (as mentioned above) because the bassmans come with an ultralinear system on the output transformer that gives is a crapload a clean headroom. I'd say get something like a cheap clean amp, and put a sansamp in front of it, or just do one of the things I've listed above..

    Cheers,

    Nish
     
  19. You need to upgrade your browser. It apparently doesn't display sarcasm... :D

    Randy
     
  20. Ben Clarke

    Ben Clarke Liquidating to fund a new business. Buy My Gear!

    Jan 6, 2005
    Western NY
    The best advice here was to get efficient cabs.

    Also, I've played a couple times with the Valve Art KT66 in my 135, and I like em so far. They have a pretty huge envelope, but they fit. They sound pretty balanced to my ears, but I have no frame of reference for this particular amp.