Mixing Power Tube Types in One Amp

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by tryan225, Sep 21, 2006.

  1. tryan225

    tryan225 Member

    Messages:
    13
    Joined:
    Sep 17, 2006
    i know this is probably a really ridiculous question, but ican't find answers anywhere

    say i had an amp that typically used four 6l6s. i get this amp to accept 6v6s.

    what would happen if i put two 6l6s on the outside tubes, and two 6v6s on the inside tubes?
     
  2. Sparky6string

    Sparky6string Member

    Messages:
    3,527
    Joined:
    Aug 22, 2005
    Location:
    Thither
  3. tryan225

    tryan225 Member

    Messages:
    13
    Joined:
    Sep 17, 2006
    ha ha...

    details PLZ
     
  4. Sparky6string

    Sparky6string Member

    Messages:
    3,527
    Joined:
    Aug 22, 2005
    Location:
    Thither
    Tee hee... just joshin ya. I don't really know, sorry.
     
  5. John Phillips

    John Phillips Member

    Messages:
    13,080
    Joined:
    Mar 17, 2002
    Location:
    Scotland
    Assuming the plate voltage is in the range that 6V6s will take (ie preferably 450V or under), it can be done - but you can't just plug in two of each and try it. The two pairs will need quite different bias voltages.

    If it's a fixed-bias amp it could be done by having a voltage-divider between the supply for the 6L6s (higher voltage) and the 6V6s (lower voltage), with two pairs of coupling caps from the PI. You could build the circuit on a small piece of tag strip, there are no more than half a dozen components needed. If it's a cathode-bias amp it's even easier, you just need separate cathode resistors and bypass caps for each pair (just two extra components needed, plus changing the value of the original resistor probably) - which is how it's done in the Mesa Blue Angel, with 6V6s and EL84s.
     
  6. jbltwin1

    jbltwin1 Member

    Messages:
    269
    Joined:
    Jan 23, 2006
    Location:
    alton, il
    If you're interested, Bob at Eurotubes sells what he calls integrated quads. Matched quads of 6L6's and EL34's that pull the same current when installed with the same control grid voltage. Might be interesting to try.
     
  7. SarasotaSlim

    SarasotaSlim Member

    Messages:
    1,413
    Joined:
    Oct 13, 2005
    Location:
    St. Pete-A-Bug FLA
    Well if ya think that's silly...

    My buddy Gregg had a BFDR that had one big coke bottle style 6L6 and one 6V6 in it and it sounded great for YEARS!
     
  8. tryan225

    tryan225 Member

    Messages:
    13
    Joined:
    Sep 17, 2006
    sweet, i will try this then...
     
  9. JJman

    JJman Member

    Messages:
    992
    Joined:
    Mar 12, 2006
    Location:
    New Jersey
    I am now also curious what would happen if one plugged in a "average" set of each type and biased in between the ideal for each. (I imagine one set could run "hot" and one "cool" under the same plate voltage, power supply and bias voltage level.) But what about the tone? Would this happy medium setting result in one set running so cold that crossover distortion would be present? Would other distortions in the output result? Good or bad? And which set "wants" stronger bias voltage under the same power supply and cathode setup?
     
  10. Mooncusser

    Mooncusser Member

    Messages:
    2,213
    Joined:
    Jul 28, 2005
    Location:
    CC, MASS/SW, FL
    You know,

    Alot of guys I know that played in the 60's era have told me that when they needed new tubes, they would just switch them like lightbulbs, and if a tube died, they simply installed a new one in it's place.
    Wouldn't this practice have damaged their amps or tubes??
    Just chiming in here~ but truly curious about this.
    Peace,
    Mass
     
  11. rockon1

    rockon1 Member

    Messages:
    11,841
    Joined:
    Aug 12, 2005
    Location:
    Stamford CT
    In my limited opinion -no it wont. In almost 30 years of playing Ive yet to bias my amps.I would like to one day since I like to tinker. I actually bought a GT probe last year and it was wired wrong! Almost blew up my amp trying to bias it.Blew the fuse instead. (yes the probe was properly installed)Now thats irony!At any rate perhaps my amps have run a bit cold or hot but they never "blew up". Thats the truth and all I got....
     
  12. Mooncusser

    Mooncusser Member

    Messages:
    2,213
    Joined:
    Jul 28, 2005
    Location:
    CC, MASS/SW, FL
    So in effect, there is no harm in not biasing an amp after new tubes are installed.?
    That is good news to hear!
    So the bias really just "optimizes" the tubes operating range?
    I'll tell you what, if what you say is true, I would love to skip the biasing process.:rolleyes: I thought it was mandatory.
    So at most, your tubes ran either cold or hot....did you notice a difference between the two extremes?
    Thanks for the tips.........
    Best regards,
    Mass
     
  13. rockon1

    rockon1 Member

    Messages:
    11,841
    Joined:
    Aug 12, 2005
    Location:
    Stamford CT
    This is only my experience. I dont recommend not biasing cause nobody else would either. Trust me Im alone on this one here and I cant blame anybody for thinking Im foolish. I just dont do it.
     
  14. Mooncusser

    Mooncusser Member

    Messages:
    2,213
    Joined:
    Jul 28, 2005
    Location:
    CC, MASS/SW, FL
    LOL!..........I hear what you are saying.
    It's just so many older players I know kept looking at me like I was crazy for obsessing over the biasing issue, I thought I'd at least ask about it here.
    Take care,
    Mass
     
  15. BluesForDan

    BluesForDan Member

    Messages:
    7,052
    Joined:
    May 12, 2006
    Location:
    NH
    actually, didn't the old simu-class mesa boogies use to have a pair each of 6L6s and EL34s?
     
  16. teleamp

    teleamp Senior Member

    Messages:
    3,508
    Joined:
    Aug 22, 2006
    Location:
    Central Texas
    Generally, as long as your not "red plating" the tubes, or giving the OT more current than it can handle, no real damage is going to occur.

    The plate dissipation of the tubes is what needs attention.
     
  17. hasserl

    hasserl Member

    Messages:
    4,734
    Joined:
    Oct 24, 2004
    Location:
    So Cal
    I've been thinking about this for some time, and I've even confered with Bob at Eurotubes about it, only using EL34's and 6V6S's. EL34's and 6V6's have similiar bias voltage needs, so it seems like it would be easier to match up a set that will bias up together than if you were using 6L6's. I've recently purchased an amp that uses four octal tubes in the power section and I will likely be giving this a try.

    ABout biasing and not biasing an amp, or paying any attention to bias. Tube amps can be very forgiving of the abuse we put them thru. But exceed the limits too much and you will have problems. With that said, people have gotten away with not checking or setting the bias in their amps for years; and never had any problems. Other people have taken very good care of their amps yet still had problems. What gives? Some people are lucky, they get away with abusing an amp for years with no failures, some people aren't so lucky.

    Some people are okay with playing an amp that is less than optimal, crappy even. To them it sounds great, maybe to you or I it would make us throw up it is so horrid, yet the owner see's nothing wrong with it at all.

    It takes all kinds to make the world go round. If you feel okay with sticking any old tube in any old position, and you get away with it, that's cool. More power to you. Some people drive cars for years never checking or changing the motor oil too. They get lucky. Other people have valves and rings and lifters stick from the varnish and sludge.

    You pays your money and you takes your chances. Do what you want. The worst that can happen is you completely destroy your amp. Hey, the world won't end if it happens. Just go get another one and go for it again.
     
  18. Mooncusser

    Mooncusser Member

    Messages:
    2,213
    Joined:
    Jul 28, 2005
    Location:
    CC, MASS/SW, FL
    Point well taken my friend.............
    Peace,
    Mass
     
  19. rockon1

    rockon1 Member

    Messages:
    11,841
    Joined:
    Aug 12, 2005
    Location:
    Stamford CT

    Hey thats me! 30 years and not a one blow'd up!:AOK As a somewhat interesting note my JSX has adjustable bias.I may have tin ears but I can not notice much(if any ) difference with the bias sweep from one side to the other. Alas....the feeling of once again being talked down to....lol Live and let live I say. And yes I did say I couldnt recommend it.....
     
  20. hasserl

    hasserl Member

    Messages:
    4,734
    Joined:
    Oct 24, 2004
    Location:
    So Cal
    I didn't mean to talk down to anyone. I'm just saying that some folks get by just fine with doing the minimum, others dont. It's all good.
     

Share This Page