Using 6V6's in place of 6L6's

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by RedLizard, May 22, 2004.

  1. RedLizard

    RedLizard Member

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    I'd like to try my Holland Lil' Jimi with 6V6's instead of the stock 5881's. I was told that if I substitute a 5U4G or 5V4GA rectifier tube for the stock 5AR4 and rebias to 20-25 mA for the 6V6's, I should be ok.

    Anybody see any problems with doing this? Other suggestions?

    Thanks in advance,

    Scott
     
  2. Jeff Flowerday

    Jeff Flowerday Member

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    They key is to make sure there isn't too much plate voltage for the 6V6. As long as the plate voltage is below 450VDC the new JJ 6V6 will handle it.

    Try a 5R4 rectifier instead of the a 5AR4 is you need a lower plate voltage.

    Note: Your output impedience will approximately double when running 6V6s. So if it was 8 ohms it will be closer to 16 ohms with 6V6s. The mismatch shouldn't be an issue but it could stress your output tranny.


    Jeff
     
  3. John Phillips

    John Phillips Member

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    What Jeff says.

    I know nothing about that particular amp, but...

    Replacing a 5AR4 with a 5U4 is only OK if the PT filament winding is rated for it - the 5U4 draws over 50% more current; without knowing for sure if the PT is up to it, I wouldn't try it. A 5V4 is OK from that point of view but has lower voltage ratings (375VAC not 450). I would check the PT secondary AC voltage first before going any further if you want to use a 5V4. A 5R4 is fine for both filament current and voltage rating, and will drop the B+ even further.

    Running the 6V6s should be OK as long as the plate voltage with whichever rectifier you choose is below about 450VDC; and if there are adequate screen-grid resistors fitted (probably 1K or more, rather than 470-ohm).

    Ideally you should double the speaker impedance (or set the selector to half what the speaker is) since 6V6s have about double the plate impedance of 6L6s; otherwise they'll be running into half their matching load which will stress them heavily - the tubes, not the OT, since it will be designed for the higher power with 6L6s anyway.
     
  4. Jon Silberman

    Jon Silberman 10Q Jerry & Dickey Gold Supporting Member

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    Wow, I'm surprised by the reactions so far. My entire life, every tech I've known has told me you can sometimes put 6L6s into a 6V6 amp with a rebias but to never put 6V6s into an amp that wants to see 6L6s.

    E.g., http://acruhl.freeshell.org/mga/main/deluxemod.html
     
  5. John Phillips

    John Phillips Member

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    Well... it's a little more complicated. Generally, yes - if you don't know what to check for, it's a very bad idea, and there is certainly no way you should just 'put' 6V6s in a 6L6 amp and expect it to work without blowing something. But not all 6L6 amps are the same.

    If the operating conditions are within the range of what a 6V6 will take, it can be done. It isn't ideal (even with a speaker load change, the primary resistance in the OT is likely to be on the low side) but it can work. Whether it sounds great or makes for the best reliability are different questions.

    In fact, in many ways a Fender Deluxe Reverb is an example of a stock amp that should really use 6L6s but does in fact run reliably enough with 6V6s! I'm quite serious. The DR has plate voltages of at least 420V usually, and is in fact mismatched for its 8-ohm load - which is more appropriate for 6L6s given the OT ratios. But you don't think twice about putting 6V6s in a DR, do you? :)

    Almost all tube guitar amp designs run the tubes above the ratings the manufacturers intended - even with 6L6s. Using 6V6s is just pushing the limits a little further.
     
  6. RedLizard

    RedLizard Member

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    With the feedback I'm getting from you guys, it doesn't sound like such a good idea to even attempt it.

    Some background: the primary reason for toying with the idea was to see if I could drop the headroom down and get some power tube breakup. The amp stays clean virtually all the way up to 12 (yes, it goes to eleven and then some!) using my Strat & Tele. Great clean sounds, just would like some earlier breakup. My OD pedals don't seem to be getting me what I want either. Sounds like the better idea might be to try some hotter pickups. I've also toyed with the idea of an an attenuator.

    Any other suggestions?
     
  7. Wakarusa

    Wakarusa Member

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    How far are you looking to drop things? Yellowjackets from THD or TADs from Smicz will certainly do the trick, but may overdo it and will affect your tone (since you'd be using EL84 or 6AK6 instead of 5881).

    A power soak (attenuator) will work also, but will wear out power tubes faster and, in a lesser amplifier, will do grave harm if used for long periods.

    The last point I'm guessing has been discussed to death btw. What it boils down to is that a properly matched dummy load won't kill the amp unless running it wide open would kill it too (something that is woefully true in too much gear).

    And, finally, you might consider a different amp that natively has the characteristics you're looking for.
     
  8. Jeff Flowerday

    Jeff Flowerday Member

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    If volume isn't an issue, I would go with a Fulltone Fat Boost, it will definately drive the amp into the Frenzy. I use one with my Princeton.

    The beauty is that it's pretty transparent, so you get the amp doing the work, you are just using the pedal to drive it harder.


    .02
     
  9. RedLizard

    RedLizard Member

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    I really love the amp and its beautiful cleans, so will try a combo of the following: attenuator, plus some different tubes (hopefully with lower headroom), Fulltone Fat Boost and a lower power speaker. If this doesn't work, then I'm probably left with...gulp...buying something a little crunchier.
     
  10. Swarty

    Swarty Member

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    FWIW, 6V6 will be biased ice cold in a 6L6 circuit. On the flipside, 6L6s will be biased very hot in a 6V6 circuit.
     
  11. Fuchsaudio

    Fuchsaudio Member

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    Why not have a local technician take a look at it, and confirm where you stand.
     
  12. Blue Strat

    Blue Strat Member

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    What Andy said. There's almost never a stock answer for any question. Knowing the particulars is what seperates "parts swappers" from amp techs.
     

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