Is there any way to compensate for the "drawbacks" of 6v6s?

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by guitguy28, Nov 27, 2004.


  1. guitguy28

    guitguy28 Member

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    I like the 6v6 for some things (low power, easy to overdrive, cool saturated sound) but to me, tonally it has a few drawbacks: mushy low end, kinda sludgy sounding when pushed hard . I use them in the Blue Angel 4x10 with Alnico speakers. A guy I know has a homebuilt 6v6 amp through a 2x12 with some kind of Eminence ceramic speakers in them, and their drawbacks are just as apparent in that setting. Is the sludgy low-end just basically something that is an unavoidable characteristic of the tube or is there a way around it (maybe running it through a JBL or something)?
     
  2. 59model

    59model Member

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    No it shouldn`t be unless you are trying to push the bass control too high. I have a Marshall Studio 15 that will compress to heck (which I love) but I have to roll back the volume control when playing chords. If you have plenty of gain, try a 12AT7 in the phase inverter (preamp tube closest to the power tubes) and it won`t push the power tubes as hard. Also check the bias so you aren`t running at more than 70% of the max power dissapation. I personally love 6V6`s, but your bottom end WILL suffer if you run the bass too high, but I`ve found that less bottom cuts through the mix and blends a heck of a lot better with your bass player and kick drum. Good luck, and if you have any ???`s email me as I own a Studio 15 and a Fargen Blackbird and don`t have the flubbs. Good luck, and don`t give up as I heard those are great amps.

    :dude
     
  3. John Phillips

    John Phillips Member

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    I'd second the 12AT7 for the phase inverter in any Mesa. It opens up the amp quite a lot, gives more clarity, less midrange and maybe a little more bass and top (although that may be due to the less mids).

    I'd also try JJ 6V6s if you haven't already - I haven't, yet, but I've heard that they are tonally a bit closer to 6L6s than most other 6V6s are.
     
  4. Jon Silberman

    Jon Silberman 10Q Jerry & Dickey Gold Supporting Member

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    NOS Philips are another option, brighter (some feel too much so!), more headroom, tighter bass.
     
  5. guitguy28

    guitguy28 Member

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    Guys, thanks for the suggestions. I did try some NOS 6v6 (Brimar) and it sounded pretty much the same to me. The Blue Angel is cathode-bias, I'm not sure if it can be adjusted or anything. I do set the bass control quite low, basically right at the point (to my ears) between too much and too little. Maybe I wasn't being accurate by saying it sounds flabby in the bass end- the best way I can describe it is it sounds mushy when I'm playing something like bent double-stops on the B and G strings.

    I do like to push the 6v6s hard though- despite the sludginess I get sometimes, the sound is great. I run the amp 3/4 volume and set the bass, mid and treble controls at 1/4 of the way up. I also use a V-Twin on a low-gain setting for extra sustain. Maybe a little bit of sludginess is something I have to live with, but I would like to try swapping out the phase inverter tube for an AT7 as was suggested. Which one would that be exactly? There are 5 12AX7s behind the power tubes. The power tubes are "in front" of the preamp tubes, going from left to right there's the rectifier tube, then the 2 6v6s then 4 EL84s. Which 12AX7 would I have to swap out- would it be the one on the left (from looking at it from the back)?
     
  6. Wakarusa

    Wakarusa Member

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    The PI is listed as V5 in the schematic. More than likely the far left tube as you look at the back of the amp.

    To change the bias, you would need to change out the cathode resistor. Something like the JJ can take serious abuse (I've personally run 'em at 440V/70mA for several minutes without even a hint of red in the plates), but I'm not sure you'd wanna hack the amp to tailor to this particular tube.

    Another question I'll throw to those more experienced with this particular amp is whether the output transformer is somehow contributing to your muddiness problem - if so, ain't no tube gonna fix it. If this is your Achilles Heel, driving it harder may actually make things worse.
     
  7. John Phillips

    John Phillips Member

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    You didn't mention that! :rolleyes:

    :)

    Yes, that will do it nicely. The V-Twin does not work well into an overdriven amp. It's not a 'pedal'... it's a full-blown preamp that happens to be in a floor box. It does not give good results into anything other than a clear-sounding, comnpletely clean amp IMO. Into an overdriven amp it produces mush and muddiness.

    What you want is a V-1 Bottle Rocket. It's a completely different thing... a tube overdrive pedal.
     
  8. guitguy28

    guitguy28 Member

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    Actually John, although the V-Twin is a dark-sounding pedal, it is not the reason for the sound of the 6v6s being the way it is. I also often use the amp on its EL84 setting as well as swapping the 6v6 tubes out for 5881s and this muddiness is not present with the other tubes.

    I guess that whether or not one would like the V-Twin with an already overdriven amp is a matter of personal taste, but I can get good sounds from it this way, with the "guitar amp out" directly into the amp's input, the Blues channel on, gain at about half, and the EQ set to taste.

    I'd also like to know if there is anything about the Blue Angel that makes the 6v6's sound different than other amp designs based around this particular tube. One day, I'd like to design and build my own amp, perhaps based on 6v6s, just because they excel with that low-watt, round sound.
     
  9. John Phillips

    John Phillips Member

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    OK... it was just my experience with the V-Twin that it does not sound good with overdriven amps (or even very thick-sounding clean ones). There's just too much conflicting preamp/EQ stuff going on, even when you run it from the guitar-amp output (which I always did). The V-1 is a wholly different thing, and maybe worth a try anyway.

    If you don't get the mush with other tubes... try other tubes! Specifically, try the JJs. I've heard people say they don't like them because they sound 'too much like a 6L6' rather than a 6V6, which should be exactly what you want if lack of low-end headroom is the problem. The Brimars (although very nice) are a typical 'vintage' soft-sounding 6V6. I have them in my Super Champ, and it does indeed flub out when pushed hard at the low end.

    Remember too, if you used 5881s and didn't get the problem, the bias was probably totally different. Rebiasing the amp for the 6V6s might be a possibility - but you definitely want it colder, not hotter, if low-end mush is the problem. You would need to find the large 270-ohm resistor in the bias circuit and replace it with a larger value - the problem is that the next 'normal' value up is 330 ohms, which is likely to be too much. You'd have to create a value in between by fitting a small resistor in series with the 270.

    I would try different tubes first... after trying a 12AT7 in the PI. As Todd says, it should be the one on the left when you look at the amp from the back.
     
  10. KLB

    KLB Member

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    You might prefer the tone of a 5751 for the phase inverter instead of a 12AT7. It has slightly more gain of 70 vs. 60, compared to 100 for a 12AX7.

    The cathode bias scheme of your Blue Angel gives you less headroom than fixed bias.

    All things considered, I like the clean tone of the 6V6 and prefer EL-84/34 tubes for power tube distortion.
     
  11. aeolian

    aeolian Member

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    Todd, so how hot would you run them in actual practice? I'm running the pair in my DR at 415V/27ma but I notice that as I saturate the amp (clipping the waveform into nearly a square wave and then pushing it even harder), the crossover distortion increases. More bias reduces this but I'm hesitant to try playing it this way to see if the distortion character changes for fear of burning something up.
     
  12. Wakarusa

    Wakarusa Member

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    Nothing like putting a guy on the spot... the answer is "it depends".

    You're already biased hotter than spec at about 80%, but if the tubes aren't turning colors and the output transformer is staying cool I wouldn't sweat it.

    Keeping in mind that we're voiding the warranty here, if it were my or my customer's amp I'd bias it out to where it sounded best for expected playing conditions (do you normally play it dimed?). If that ended up being beyond published spec I'd play it while looking for glowing plates or an overheated OT. I'd also make sure the screen resistors are up to snuff just in case we're all wrong about what the tube will tolerate.

    More caveats:
    To be meaningful, the test playing (while watching the amp like a hawk) needs to be expected conditions. That means that if you're going to gig the amp you need to see if it will survive 3 or 4 hours straight.

    Also, if I arc a socket it's pretty easy for me to fix.

    I'm interested in your results re: xover distortion. Have to put my SFDR on the scope and see what happens.
     

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