Replacing 6V6s in an Allen Accomplice with 6L6s

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by iim7v7im7, Jun 26, 2008.

  1. iim7v7im7

    iim7v7im7 Member

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    Hi,

    I own an Allen Accomplice Head that I use with a 1 x12" cabinet outfitted with an Eminence RW&Bs. I wanted to experiment to see what 6L6 power tubes sound like in the amp.

    Musically, I mostly play blues (Fender Nocaster) and occasionally jazz (Heritage archtop). For distorted tones, I tend to drive the amp with some OD pedals.

    The amp currently has JJ 6V6s installed in it (22w). It will begin to break-up somewhere between 3 and 4 on the volume control. I am hoping for increased headroom and a somewhat less dark tone.

    Who's 6L6s should I consider and why? What online dealers should I consider buying from?

    Thanks,

    Bob
     
  2. Blue Strat

    Blue Strat Member

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    Definitely consider the SED 6L6GCs. Excellent track record for longevity and tone.

    Be sure to rebias no matter which brand you choose.
     
  3. Structo

    Structo Member

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    Don't the output tubes like to see a different primary impedance from the output transformer on those two different tubes?
    Something like 8K for 6V6's and 4K for 6L6's?
     
  4. teleamp

    teleamp Senior Member

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    The Accomplice has a speaker ohm selector that lets you use the 4 or 8 ohm OT taps, when using 6L6's you switch to the 4 ohm setting and use with the 8 ohm speaker so that the 6L6's are seeing 4K.


    And, another vote for the SED 6L6's, rugged robust tubes.
     
  5. iim7v7im7

    iim7v7im7 Member

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    Hi,

    I think because power tubes are relatively inexpensive, I will try two alternative sets:

    - JJ/Tesla 6L6GCs
    - SED S6L6GCs

    Additionally, I may try alternative pre-amp tubes after first comparing the 6L6 sound to the 6V6 sound. I will curious to see how my OD pedals work with the 6L6s. They work well with the 6V6s.

    :)

    Bob
     
  6. picnic

    picnic Supporting Member

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    I had Sovtek's in my Accomplice. There wasn't much difference in the tone from 6V6's
     
  7. bbarnard

    bbarnard Member

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    I believe Allen also recommends a rectifier change when you do the 6v to 6L swap. Check with him on that.
     
  8. teleamp

    teleamp Senior Member

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    Nah, GZ34 for either 6V6 or 6L6, just switch the speaker impedence and rebias, simple. The Allen has the bias test points on the back of the chassis and the bias pot is underneath the chassis.
     
  9. hasserl

    hasserl Member

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    I think you've got that backwards Mike.

    If 8 ohms into the 8 ohm setting results in 8k primary Z, and
    4 ohms into the 4 ohm setting results in 8k primary z, then
    8 ohms into the 4 ohm setting will result in 16k primary Z.

    Not a good thing for 6L6's.

    4 ohms into the 8 ohm setting will result in 4k primary Z
     
  10. Blue Strat

    Blue Strat Member

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    The bottom line is (bypassing our knowledge of primary Z) that 6V6s want to see about 2X the load impedance that 6L6s do.
     
  11. tommytomcat

    tommytomcat Member

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    My guess is Dave uses a 35w bandmaster/pro/tweed super style OT in that amp. If that's so, it has a 4K primary for 6L6's and the secondaries = 4 & 8 oms. When using 6v6's the 4 ohm tap will = 8 ohms (8 ohm tap will = 16ohms).. so either way, one of those taps will = 8 ohms for your single 12. Email Dave and he'll tell you for sure. +1 for the SED's.
     
  12. dougk

    dougk Silver Supporting Member

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    Your right.

    I've been playing for a while on my Encore and I think I've finally found the setup I really like. Started with JJ 6v6's, then some NOS Phillips, then 6l6's I "borrowed" from my bassman and now JAN 6l6 Phillips I bought from http://www.unclespot.com/ and LOVE those.

    Make sure you use the correct rectifier when you do the swap and rebias.
     
  13. teleamp

    teleamp Senior Member

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    Thanks, the Accomplice has a switch for 6L6 or 6V6, I have forgot the details. The amp comes with a 8 ohm speaker and an OT with two output impedances (in one position the tubes see 4K and they see 8K on the other). I have built two Accomplices and they run either tube, its just a matter of r&r power tubes, flick a switch and a rebias, which is a breeze on the Accomplice.

    And, if you change rectifier types, you will need to rebias as well. But the Accomplice ships with a GZ34 that is for use with 6V6's or 6L6's.
     
  14. bbarnard

    bbarnard Member

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    That's not what Allen told me when I asked him that very question when I owned my Old Flame. He suggested a rectifier change as well.
     
  15. teleamp

    teleamp Senior Member

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    From the Allen website about the Accomplice: "Tube Compliment (4) 12AX7, (2) 6V6GT or (2) 6L6GC, and (1) GZ34".

    I've used 5Y3GT, GZ34, and 5U4GB, and the only thing I had to do was check and adjust the bias if needed.
     
  16. Blue Strat

    Blue Strat Member

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    What plate voltage are you getting with 6V6s and a GZ34?
     
  17. teleamp

    teleamp Senior Member

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    I'll see one of the Accomplices that I take care of in a week or two, I'll check.
     
  18. hasserl

    hasserl Member

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    That's the same as you posted before, it's backwards. The turns ratio between the primary coil and the 4ohm coil is greater than it is between the primary and the 8ohm coils. The ratio between the two coils is what determines the transformation ratio. The same load applied to the 4 ohm tap will result in twice the primary impedance than the same load applied to the 8 ohm tap. If the schematic says otherwise it's wrong, probably a misprint.
     
  19. teleamp

    teleamp Senior Member

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    OK, I emailed David Allen, here is the scoop...

    "6L6s like a plate load impedance of around 4,000 ohms while 6V6s like a plate load impedance about twice that or 8,000 ohms. So by doubling the speaker load connected to the secondary of the OT, we reflect twice the impedance to the primary as the OT is just a constant "voltage ratio" and "impedance ratio" device. So on the Accomplice, there is a 4 and 8 ohm setting with 6L6s and an 8 and 16 ohm setting with 6V6s. Luckily it works out that there is a switch position for an 8 ohm speaker load for both types of power tubes. It is almost like the impedance switch is a power tube selector for an 8 ohm speaker load.

    Hope that helps.

    David
    "
     
  20. hasserl

    hasserl Member

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    And I agree with that, it is correct. David in the man. :cool: (it is the opposite of what was posted above though, but that's cool, we got it straight now)
     

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