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Thread: Please recommend me tubes for my Bassman

  1. #1
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    Please recommend me tubes for my Bassman

    Howdy,

    I recently purchased a silverface 70 watt Fender Bassman Ten amplifier. It has an ultralinear OT and two 6L6GC tubes in the output section. Since it's old, I'm doing a cap job and decided to replace the output tubes as well. I have basically two options in my local store, the cheaper 5881WXT (branded Fender Groove Tubes) and the more expensive JJ 6L6GC.

    Which ones would you recommend? I don't play very loud and keep it mostly in the clean/blues area. Since money is an issue, I was thinking going for 5881WXT's. Are they up to withstanding the higher plate voltages and dissipation requirements? Is their sound any good?

    Thanks for any advice!

  2. #2
    Supporting Member Jazz P Bass's Avatar
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    What is wrong with the tubes that where in the amp?

  3. #3
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    Well, the first thing I noticed is they are not made by the same manufacturer. One is branded Fender, the other one Zenith and they look very different regarding internal construction. One is short and fat and the other tall and thinner. As far as I know, the point of push-pull output stages would be to ideally have identical amplifying devices for both half-periods of the input signal.

    I have no way of telling how old or worn the tubes are either, so I thought it would be best to replace them.

    The amp doesn't sound bad, I just thought new tubes would make it sound a little better.

  4. #4
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    The amp needs to be adjusted to suit output tubes, process referred to as biasing. It would be a bad idea just to fit them yourself; far more beneficial, in terms of tone, tube life and amp reliability, for a competent experienced tech to do this.
    He should be able to fit the tubes, bias the amp and give it a basic checkover for a minimum bench fee. The checkover may reveal that further work would be beneficial.
    The Fender UL amps can be very hard on the output tubes, if the amp is overdriven; there's another thread on 'best current production 6L6GC' in which recommendations were made (Sovtek 6L6GC WXT+ = Electroharmonix 6L6GC from memory) for these amps.
    Pete.

  5. #5
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    Thanks for your reply! As far as I can tell from the schematic, my Bassman has a fixed bias and only a bias balance pot. There is no way to adjust the overall bias voltage without modifying the original circuit. I planned on installing new output tubes, measuring and balancing their idle currents. If these values are out of specs according to the datasheet (e.g. excessive anode dissipation for the measured plate voltage), I'll have to throw in another trimmer to allow for true bias level adjustment.

    As far as output tubes go, I can basically choose between Fender 6L6 Groove Tubes (which is a re-branded 5881WXT) and JJ 6L6GC from the shop or some chinese made 6l6GC rebranded as Mesa STR-440 from my country's equivalent of craigslist.

    Which ones do you think I should get? Thanks for all your help people!

  6. #6
    ToneOholic! big_teee's Avatar
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    Here's a 6l6 tube review using a Bassman.
    "Wild Bill" Costello 6L6 Review
    John Templeton's 6L6 / 5881 Tube Review
    I buy tubes from TubeDepot.
    They have about the best prices in my area.
    6L6 / 5881 / KT66 / 7027 Tube Types
    I have the Sovtek 6L6WXT+ in a Traynor Amp.
    They are 3 years old and sound great.
    Good Luck,
    Terry
    Technicians Run the World, but Bankers, Lawyers, and Accountants, Take All The Credit!
    Keep Rockin! B_T
    Terry

  7. #7
    Supporting Member Jazz P Bass's Avatar
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    I would go with the Sovtek 6L6 WXT.
    Make sure you check the bias though, as they do tend to run hotter than other tubes.

  8. #8
    Old Timer Gtr_tech's Avatar
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    I haven't had good luck with the 6L6wxt+ and its variants in an ultralinear output section, so I dunno if I'd go that route. The JJ is a stout tube and should be fine in that application. The EH/Sovwreck wxt+ is fine in a standard non screen tapped output section, but for whatever reason doesn't like UL operation.

    The Ruby 6L6GC-MSTR is a good sounding durable tube as well.
    The farmer takes a wife, the barber takes a pole....

  9. #9
    ToneOholic! big_teee's Avatar
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    What about Tung Sol Reissue 5881s?
    I Have read where they are supposed to be a good match for the Bassman Circuit.
    B_T
    Technicians Run the World, but Bankers, Lawyers, and Accountants, Take All The Credit!
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    Terry

  10. #10
    Old Timer Gtr_tech's Avatar
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    I wouldn't use a "real" 5881 in anything but a tweed bassman setup.

    I need clarification here. Is this amp a "Bassman ten" or a "Bassman 70"? They are very different amps. The Ten you can use pretty much any good quality 6L6 type. The "70" will eat substandard tubes in no time due to the UL operation.
    The farmer takes a wife, the barber takes a pole....

  11. #11
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    This is a "Bassman Ten" but manufactured after they switched them to UL. Five wires out of an OT primary is too much for a classic power amp. I googled the output transformer markings and it checks out. Basically, it has a very similar circuit to the 70.

    I'd like to thank everyone for the input, I'll probably go JJ to be on the safe side.

  12. #12
    Old Timer Gtr_tech's Avatar
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    Yea, if thats UL don't use 5881s in it (unless its the Sovtek 5881, which ain't a 5881 at all). I generally look at a 5881 as a 6L6g, since they're close to that in specs.
    The farmer takes a wife, the barber takes a pole....

  13. #13
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    My personal favorite in that application is the TungSol 6L6GC. Really nice sounding tubes for a good price, and they seem to have a good life span. New Sensor really got this one right.
    John R. Frondelli
    dBm Pro Audio Services, New York, NY

    "Mediocre is the new 'Good' "

  14. #14
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    I'll second that!

  15. #15
    Senior Member Enzo's Avatar
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    And that bias balance? Ther is a simple and easy way to do that, it is how the factory tells you to do it.

    Warm up the amp with a speaker connected, no guitar plugged in, just amp alone. Then listen to the speaker closely - scan the balance control back and forth to the setting that minimizes any hum. That is the balanced condition, it cancels power tube stage hum. You also null the heater hum balance on amps that have one the same way.

    You can get out the bias probes and measure this and that, but the reason to balance the outputs is to set it symmetrical. And equal idle DC currents isn't necessarily as well balanced as simple audio nulling because of things like differences in transformer winding resistance.
    Education is what you're left with after you have forgotten what you have learned.

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