Tried El34's In The Afd 100

Discussion in 'Marshall Amps' started by lespaul6, Apr 26, 2019.

  1. lespaul6

    lespaul6 Member

    Joined:
    Dec 13, 2007
    Messages:
    71
    Likes Received:
    56
    Location:
    Florida
    It sounded ok? I guess.. seemed to be just as loud as 6550's but the bottom was "lifting" up differently when muting etc. I like the 6550's better in this amp.

    The factory setting on the 6550's was in the 40's does this seem too underbiased and stressful to the power transformer?

    When backed off to around 38 it sounded weaker with less high end cut... didn't make any sense to me, it should be brighter at that setting.
     
  2. charveldan

    charveldan Well-Known Member

    Joined:
    Jan 31, 2010
    Messages:
    7,677
    Likes Received:
    4,552
    Location:
    Somewhere with a Friedman Marshall & Les Paul.
    Whats your plate voltage ?
    Bias is set in relation to PV.
    That amp has an auto-bias feature i believe.
     
    MarshallDog likes this.
  3. lespaul6

    lespaul6 Member

    Joined:
    Dec 13, 2007
    Messages:
    71
    Likes Received:
    56
    Location:
    Florida
    About 470-480
     
  4. charveldan

    charveldan Well-Known Member

    Joined:
    Jan 31, 2010
    Messages:
    7,677
    Likes Received:
    4,552
    Location:
    Somewhere with a Friedman Marshall & Les Paul.
    Bias for 6550 per tube should be around 52ma @ 470 plate volts.
    EL-34's should be around 37ma @ 470 plate volts per tube.
    Thats 70% dissapation.
     
  5. anitoli

    anitoli Well-Known Member

    Joined:
    Jul 9, 2011
    Messages:
    5,728
    Likes Received:
    5,859
    Location:
    Lewiston, Maine U.S.A.
    You don't have to bias at 70%. You can bias much lower. Let your ears decide. The colder the longer the tube life and more headroom in the power amp.
     
  6. mickeydg5

    mickeydg5 Well-Known Member VIP Member

    Joined:
    Sep 30, 2011
    Messages:
    20,036
    Likes Received:
    7,913
    Location:
    US of A
    At those plate voltages biasing in the middle 40's mA range is preferred.

    The recommended bias current settings are right there in your manual, at 120VAC wall supply anywhere from 32mA - 47mA is good.

    It gets a bit more clarity and top end with higher settings so turn it up enough to get that. It is not stressing your amplifier.

    DO NOT USE THE 6550 35/42 WATT PLATE DISSIPATION FOR CALCULATIONS. THIS AMPLIFIER IS DESIGNED AROUND A 25W DISSIPATION.

    :metal:

     
  7. lespaul6

    lespaul6 Member

    Joined:
    Dec 13, 2007
    Messages:
    71
    Likes Received:
    56
    Location:
    Florida

    There is definitely a point where that clarity you are talking about "pops" and its always in the same place. I wish I had a manual but I bought it used. Looks like the bias control was never touched- based on some photos Ive seen online. I will leave it there (around 41ma). The original tubes are now 8yrs old so they probably need to be changed out anyway. thanks for all the recommendations gentleman
     
    Mitchell Pearrow and charveldan like this.
  8. mickeydg5

    mickeydg5 Well-Known Member VIP Member

    Joined:
    Sep 30, 2011
    Messages:
    20,036
    Likes Received:
    7,913
    Location:
    US of A
  9. ampmadscientist

    ampmadscientist Well-Known Member

    Joined:
    Jun 26, 2014
    Messages:
    11,614
    Likes Received:
    5,658
    Location:
    Left Coast

    "...seemed to be just as loud as 6550's but the bottom was "lifting" up differently ..."

    How did you bias it?

    "The factory setting on the 6550's was in the 40's does this seem too underbiased and stressful to the power transformer...?"

    How do you know it was the factory setting?
    The factory will bias it cold, to make the tubes last longer. They don't need to replace any tubes under warrantee. :lol:

    If the bias is cold, it's less stressful to the PT.
     
  10. lespaul6

    lespaul6 Member

    Joined:
    Dec 13, 2007
    Messages:
    71
    Likes Received:
    56
    Location:
    Florida

    I figured most folks crank the master and attenuate it down so the tubes were getting worked for the last 8yrs... but I could be wrong of course. Here it is with power on ten and master at minimal tv volumes:

     
  11. MarshallDog

    MarshallDog Well-Known Member

    Joined:
    Nov 28, 2010
    Messages:
    10,214
    Likes Received:
    8,102
    Location:
    Taintville
    Nice tone and playing Bro!?
     
  12. solarburnDSL50

    solarburnDSL50 Well-Known Member

    Joined:
    Aug 8, 2008
    Messages:
    15,178
    Likes Received:
    8,055
    Location:
    Wetville
    I know Mickey is being accurate. It matters how much much mileage is on them.

    If it was me? Put some new 6550's in. You can't say the mileage yet you know they are 8 yrs old? Id replace them. That's me.

    6550's kick ass. I like 34's too but I'd be right at home with the 6550's feeling I have the amp right in its sweet spot. To each their own.
     
  13. mickeydg5

    mickeydg5 Well-Known Member VIP Member

    Joined:
    Sep 30, 2011
    Messages:
    20,036
    Likes Received:
    7,913
    Location:
    US of A
    If they have the bottom through top end and still sound good then do not trash them. If sounding good you cannot tell if worn unless tested on a good tube tester. They may test just as good or better than other new power tubes. Buy another set and compare. Keep a set for backup.

    That is all I am getting at, common sense.
     
  14. solarburnDSL50

    solarburnDSL50 Well-Known Member

    Joined:
    Aug 8, 2008
    Messages:
    15,178
    Likes Received:
    8,055
    Location:
    Wetville
    Always great advice that I'd take. 8 yrs of use and only ears to measure with? I'd replace and keep the 8 yr old as spares. However 6550's are not cheap at a quad.
     
  15. Mitchell Pearrow

    Mitchell Pearrow Well-Known Member

    Joined:
    Jul 2, 2018
    Messages:
    5,706
    Likes Received:
    7,156
    Location:
    Moreno Valley CA
    Your tone is kicking ass, playing is doing the same, what my brother’s before me said is great advice and they know what there talking about! Cheers Mitch
     
    lespaul6 likes this.
  16. Chris-in-LA

    Chris-in-LA Active Member

    Joined:
    Jul 19, 2018
    Messages:
    476
    Likes Received:
    219
    Sounds great to my ear. But, I usually crank the pre-amp, not the master at living room volume. I was under the impression that was more common than the way you described.
     
    Mitchell Pearrow likes this.
  17. MarshallDog

    MarshallDog Well-Known Member

    Joined:
    Nov 28, 2010
    Messages:
    10,214
    Likes Received:
    8,102
    Location:
    Taintville
    Thats exactly what Id do!!
     
  18. Squidhunter

    Squidhunter Active Member

    Joined:
    Feb 5, 2015
    Messages:
    317
    Likes Received:
    181
    Location:
    Brisbane
    6550's all the way...I experimented with KT66's and EL34's a few years back, the 6550's were just right, from memory they were just made for the amp it seems.
    Back when the amp was released I couldnt believe some negative posts on what people described as a disappointing amp.
    After owning and playing a shit load of marshals the AFD just kicks ass.
    Its a monster amp!
     
  19. lespaul6

    lespaul6 Member

    Joined:
    Dec 13, 2007
    Messages:
    71
    Likes Received:
    56
    Location:
    Florida

    +100 there is a lot of jubilee in this thing so anyone who loves a good 2555 would love these amps- plus you dont have to have any outboard boost or EQ to get you there- its perfect.
     
    Squidhunter and Mitchell Pearrow like this.

Share This Page

  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.
    Dismiss Notice