Is switching between 6L6 and EL34 just matter of re-biasing?

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by ari, Oct 29, 2004.


  1. ari

    ari Member

    Messages:
    982
    Joined:
    Feb 26, 2004
    Location:
    St. Paul, MN
    Or does it require changes in other parts of the circuit?

    Thanks,

    ari
     
  2. theelectic

    theelectic Guest

    Nope. Depends on the amp. If the amp was designed for 6L6s and 6L6s only, then the tube socket will have to be re-wired (and a couple of parts installed) for EL34s, then re-biased.

    Think of it this way: an EL34 wired socket can accept a 6L6, but a 6L6 wired socket cannot accept an EL34. Once the socket is wired for an EL34, you can use both.
     
  3. clay_finley

    clay_finley Member

    Messages:
    67
    Joined:
    Dec 4, 2003
    Location:
    Austin, TX
    Also the heater current on EL34 is 1.5A and the heater current for 6L6 is 900mA.

    So If the amp originally had 6L6's, then the PT may not be able to supply the required heater current for EL34's (since it's close to double). This is even worse if there are 4 power tubes.
     
  4. Blue Strat

    Blue Strat Member

    Messages:
    30,013
    Joined:
    Aug 2, 2002
    Location:
    Sterling, VA (not far from Washington DC)
    ...plus you may need to change the resistor in series with the bias pot in order to get EL34s into the proper bias range.

    Sometimes not.
     
  5. hipfan

    hipfan Member

    Messages:
    2,302
    Joined:
    Nov 15, 2002
    Location:
    Evanston, IL
    Sorry to resurrect an old thread, but this seemed to be the appropriate place for this follow-up question.

    Is there also an issue with the impedance the OT wants to see, when switching from 6L6's in an amp designed around those tubes, to EL34's? For instance, in a thread on the HC amp forum, James Peters mentioned that, when running EL34's in the Peavey 5150, it could be a good idea to use the 16 ohm tap for the user's 8 ohm cab.

    I'm wondering what the technical reason is for this. Does this hold true for all 6L6-designed amps where the user is trying to use EL34's?

    Specifically, I have a Demeter TGA2 50 watter that is designed to use 6L6's. On my request, the guys at Demeter set the amp up for use with EL34's (bias circuit, pin connections), but it still has the same transformers as "stock" TGA2's. Should I use the 16 ohm tap for my 8 ohm cab when using 6L6's? Are there any reasons (other than sound quality preference and the heater current issue noted by Clay) why it might be a bad idea to run EL34's in an amp designed around 6L6's?

    Thanks for any help.
     
  6. Blue Strat

    Blue Strat Member

    Messages:
    30,013
    Joined:
    Aug 2, 2002
    Location:
    Sterling, VA (not far from Washington DC)
    The output impedance is close enough.
     
  7. hipfan

    hipfan Member

    Messages:
    2,302
    Joined:
    Nov 15, 2002
    Location:
    Evanston, IL
    Mike - Thanks. I take it that you mean that the output impedance is close enough that running an 8 ohm cab from the 8 ohm tap is the right way to go?

    Is that generally true universally for 6L6 amps using EL34's, or is your statement specific to the Demeter? Just curious. Thanks again!
     
  8. Blue Strat

    Blue Strat Member

    Messages:
    30,013
    Joined:
    Aug 2, 2002
    Location:
    Sterling, VA (not far from Washington DC)
    It's a generic statement regarding 6L6s and EL34s.
     
  9. hipfan

    hipfan Member

    Messages:
    2,302
    Joined:
    Nov 15, 2002
    Location:
    Evanston, IL
    Ah, OK. Thanks.

    I did some testing this evening, and the amp definitely sounds best (i.e. more volume, less compressed, more articulate and open) IMO with the 8 ohm cab on the 16 ohm tap. There is a more compression and less volume using the 8 ohm tap with the 8 ohm cab. As long as I'm not hurting anything, I'll probably keep it mismatched when running EL34's.

    Interesting stuff. (to me at least! :D )
     

Share This Page