el34 and 6l6, interchangable?

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by mlynn02, Sep 25, 2005.

  1. mlynn02

    mlynn02 Member

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    i know there are some amps that can take both el34's and 6l6's with a bias adjustment. can any amp that takes el34's also run 6l6's, or are they different enough that only certain amps can do it?

    thanks,
    matt
     
  2. Blue Strat

    Blue Strat Member

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    No absolute generalizations can be made here. EL34s consume more heater current and can kill a power transformer designed for 6l6s, though it's unlikely.

    Biasing is always necessary and some amps may require a resistor change in order to accomodate the alternate tube type (to bias them properly).

    Tube sockets in amps designed for EL34s are always correct for either type, but the opposite is not always true.
     
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  3. mlynn02

    mlynn02 Member

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    so generally it's more likely that an amp designed for el34's can accept 6l6's than the other way around? that said, is it rare that the swap results in a good tone?
     
  4. Blue Strat

    Blue Strat Member

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    Yes to the first part.

    To the second part, there is no answer. Only YOU know whether it's good or not. There's absolutely NO consensus regarding what GOOD tone is.
     
  5. drbob1

    drbob1 Silver Supporting Member

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    A lot of 6L6 amps use one of the pins that the EL34 needs as a tie point for grounding, so it doesn't work (particularily Fenders). Groovetubes actually built some amps you could swap EL34s for 6V6 because the bias voltages are closer (especially if you keep plate voltage down). I can see places where switching a 6L6 into an El34 slot might be useful (say the Traynor Guitarmaster? with the 4 El34s would have a cleaner, punchier tone with 6L6s).
     
  6. TheAmpNerd

    TheAmpNerd Member

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    Isn't the
    primary impedence that el34s "require" roughtly the same as
    the 6V6 "require", 8k for the former versus about 4K for the 6L6.

    OR

    4k (el34) versus 2K (6L6) depending on tube count.
     
  7. Blue Strat

    Blue Strat Member

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    Yes, 6V6s are a good match (same bias current, on average, too). They're all close enough.
     
  8. KLB

    KLB Member

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    The standard primary impedences for these tube sets are:

    2 x EL34 = 3.4K
    4 x EL34 = 1.7K

    2 x 6L6 = 4K
    4 x 6L6 = 2K

    Putting 6L6 in an EL34 amp will not quite load the tube enough if the impedence selector matches the speaker load, but you may like the sound.

    6L6 input grids are not as sensitive as EL34, so the relationship to the preamp changes. Also, you may prefer a change in negative feedback values going from EL34 to 6L6.

    FWIW, I've tried subbing 6L6 in various EL34 amps and always go back to the EL34.

    In low voltage (430v) Bassman/Plexi amps designed around EL34, I have had good results subbing 6V6 and setting the speaker impedance selector one-half the speaker load, and also using a 12AT7 or 5751 for the phase inverter.

    What amp are you thinking of swapping tubes?
     
  9. TheAmpNerd

    TheAmpNerd Member

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    Thanks KLB.

    I was thinking the impedences varied more than that.
     
  10. waxnsteel

    waxnsteel Member

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    So, can you put EL34's in a 6V6 amp? PArdon my ignorance, I've never owned an EL-34 amp, and I haven't asked many questions regarding them.
     
  11. KLB

    KLB Member

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    IT ALL DEPENDS!!
    Almost never in a 2-6V6 amp, although there are a handful that this is OK. It is probably OK in a 4-6V6 where you pull all tubes and install just a pair of EL-34. Here are some things to look for:

    FILAMENT CURRENT
    The filament current draw for EL-34 is 1.5 amps each, where for a 6V6 it is only .45 amps (6L6 is .9 amps). The 6.3v filament tap on the power transformer has to be capable of providing enough current for the power tubes, preamp tubes and pilot light.

    POWER TUBE SOCKET WIRING
    The original 6V6 amp has to have the power tube socket pins 1+8 tied together and to ground. Pin 1 is usually not grounded in a 6V6/6L6 amp unless the designer intended for substituting EL34. This can be easily modded.

    BIAS RANGE
    You need to rebias, and the bias range usually works OK going from 6V6 to EL34 in a FIXED bias amp. For a cathode biased amp, the bias resistor will probably need changing to a larger value.

    TRANSFORMERS
    The ideal output transformer primary impedence for a quartet of 6V6 is about the same as a pair of EL-34 (3.4K), so there is no need to set the impedance selector different than the speaker load. For a single pair of 6V6, you will want to use an impedance tap one higher than the speaker load. That is, an 8 ohm load with the 16 ohm tap.

    EL34 may not sound good in the 6V6 amp even though they technically work OK. This is because both the power and output transformers may be undersized to realize the full potential of the EL34. Again, almost certainly true if replacing 2-6V6 with 2-EL34, probably true if replacing 4-6V6. You may not perceive much if any volume increase, just a tone change.

    PHASE INVERTER GAIN
    The phase inverter component values to drive a 6V6 vs. EL34 are different. 6V6 grids don't take as much signal to saturate, so using EL34 may not be ideal. This is easily modded.

    SPEAKER HANDLING
    Assuming the power and output transformers can provide enough current and headroom to achieve 35-55 watts from a pair of EL-34, you have to be sure the speakers can handle the extra wattage.

    GET THEE TO AN AMP TECH!
    Since you have to ask.... Best to take it to an amp tech to be sure about all these and possibly other factors.

    MY EXPERIENCE
    I have not experienced a 2-6V6 amp that sounded good with EL34, even though technically OK. However, I have liked the sound of some 4-6V6 amps with a pair of EL34, such as the Tone King Meteor II and Carr Slant 6V. I have also enjoyed using a pair of 6V6 in 2-EL34 amps, such as the Germino Club 40. (The issue here is plate voltage, which is 430 in the Club 40.)

    - Ken
     
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  12. deeval

    deeval Supporting Member

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  13. KLB

    KLB Member

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    Deeval,
    EL34 are cool in the TK Meteor II! I liked the tone, especially clean. Since you play(ed) an EL84 TremCat (right?), you might like the tone, too.

    If you try a pair, experiment with the bias, going from 36ma to 50ma, or even slightly higher. The cooling fan keeps the heat buildup under control. Also, try mixing a 6L6 and EL34 and bias the 6L6 hotter (experiment!). It takes more grid signal to drive a 6L6 than an EL34, so this helps "balance" the two tubes.

    You can play around with the push-pull symmetry in the TK MII by biasing one tube (or pair) cold and the other hot. Half power uses tubes 1 and 2. In full power with four tubes, the pairs are 1+3 and 2+4. Full power with two tubes is 3 and 4. With 4-6V6, you can bias the half power pair 1-2 hot and the full power added pair 3-4 relatively cold. Lots of toneful variations are possible!

    I am using 4-6V6 now because I am experimenting with a 20watt Celestion Heritage G12M20 and half power to get the volume down. I like the TK1891 speaker a lot, but wanted to try something different. Th G12M20 is less efficient than the TK1891, and is somewhat brighter, but smoother to my ears for OD, with a seductive feel and touch response. I just ordered a TK 1x12 extension cabinet (with stock TK 1891) so I can add a 2nd G12M20.

    My favorite cranked tone from the MII Lead channel is using a pair of small-bottle 6L6-WGC (TAD/Shuguang) biased at 50ma. I plan to try the new TungSol 5881, too. IMO, the MII lead channel voicing works better with 6L6/6V6 than EL-34.

    However, my favorite overall distortion tone is probably a cranked pair of EL34 in a 40-50w JMP/Plexi 4-input circuit. No one amp (or tube type) does it all for me.

    - Ken
     
  14. deeval

    deeval Supporting Member

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    Very Cool!
    I will have to try it,Man is the Metero II one killer tone Machine,
    I also found that the TAD,s in my Fuchs ODS also sound very good I use those instead of the 6V6,
    Thanks for the info.:dude
     
  15. schwimbo

    schwimbo Member

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    KLB posted (several years ago):

    TRANSFORMERS
    The ideal output transformer primary impedence for a quartet of 6V6 is about the same as a pair of EL-34 (3.4K), so there is no need to set the impedance selector different than the speaker load. For a single pair of 6V6, you will want to use an impedance tap one higher than the speaker load. That is, an 8 ohm load with the 16 ohm tap.

    I'm not sure that I agree with the above statement. I would think that the pair of 6V6 would have double the impedance of a quartet of 6V6 and so would require either a speaker with double the original speaker impedance into the original speaker tap (16 ohm speaker into the original 8 ohm tap), or use the original 8 ohm speaker into a 4 ohm tap. The lower value speaker taps are wired into fewer windings on the secondary, so the primary to secondary ratio is higher, which it would need to be if you substituted tubes that require a higher a higher primary impedance, or if you used a speaker with lower impedance. The reflected impedance of the secondary would be greater (for a give speaker load) when a lower impedance speaker tap is used. At least, this is my understanding of the subject.
     
  16. rkstaton

    rkstaton Member

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    Ok, this question is somewhat related to the topic. I have a JCM2000 which recently died on me, the apparent cause being one of the EL34's going out(it's a 50w model so there are only two). If i were to buy a set of 6v6's when I get my EL34's would either one work fine in the amp? I assume that since the amp is set up for 50w operation that there would be no problems running a set of 6v6's with lower filament current, and lower output power. Would this essentially turn my 50watt DSL into a 20-30 watt model that saturated easier?? I also ask because I would eventually like to build my own trainwreck express and as I understand it people like to use 6v6's in place of EL34's sometimes so that the
    wreck doesn't blow their head off(since there's no master volume).
     
  17. big mike

    big mike Moderator - EL34 Emeritas Staff Member

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    I swear to god this is getting chisled on my headstone.
     
  18. big mike

    big mike Moderator - EL34 Emeritas Staff Member

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    Way different designs. Fisher (and the clones based on his design) are built in mind to take the 6v6's. Just 'dropping' 6v6's into a DSL is recipe for disaster IMO.

    It would need a serious rebias, and likely several resistor changes to get it into safe range IF the OT can handle it.

    Stick with EL34's. DSL's have decent master volumes. Wreck's dont.
     
  19. grb718

    grb718 Member

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    Depends on amp.
    I have a Germino classic 45 that can run 6L6 or kt66's.
    Sounds good with both but absolutely requires a re-bias when switching tube types.
     
  20. Tony Bones

    Tony Bones Member

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    Good answer, but why'd it take you more than five years to come up with it?
     

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