Power tubes matched?

Discussion in 'The Workbench' started by Emtbreid, Aug 31, 2019.

  1. Dogs of Doom

    Dogs of Doom Moderator Staff Member

    Joined:
    Aug 2, 2012
    Messages:
    20,613
    Likes Received:
    21,412
    Location:
    Los Angeles
    Micky should have a thread about fine-tuning that amp. On the DSL, Marshall's recommended biases were hot. Many people have found that running them lower bias, helped the amp breathe a bit & opened it up.

    I'm not sure about the EL84s though. Marshall recommended 90mv on the 100 watters (45mv/tube) Many people like the bias in the 30s better. So, running around 37mv is more ideal. I think I've even seen a few people say that they like it at 32mv...

    Both are pretty far from the Marshall recommendation.

    Also, the tubes should last longer.

    I'm not sure at the .55mv you're getting, or what EL84 tubes are supposed to run at, but, maybe look around Micky's thread...
     
  2. Dogs of Doom

    Dogs of Doom Moderator Staff Member

    Joined:
    Aug 2, 2012
    Messages:
    20,613
    Likes Received:
    21,412
    Location:
    Los Angeles
  3. Emtbreid

    Emtbreid Well-Known Member

    Joined:
    Oct 22, 2018
    Messages:
    585
    Likes Received:
    611
    Location:
    East Coast, USA
    Yeah, the pre 2003 models were supposed to be biased at 1.375v, way too hot. Mine is a 2004 (confirmed that my board has the resistor changes that they made), and a paper I got from Marshall recommended between 540 and 560mv. Believe 560mv gives 14ma per valve, so I set in between. I’ll check out his thread. Setting at 550 sounds good for now.
     

    Attached Files:

    Dogs of Doom likes this.
  4. Dogs of Doom

    Dogs of Doom Moderator Staff Member

    Joined:
    Aug 2, 2012
    Messages:
    20,613
    Likes Received:
    21,412
    Location:
    Los Angeles
  5. Emtbreid

    Emtbreid Well-Known Member

    Joined:
    Oct 22, 2018
    Messages:
    585
    Likes Received:
    611
    Location:
    East Coast, USA
    Thank you! I’d seen John H stating he biased up to .700mv, but I also thought I’d seen someone state that was pretty hot? I checked the bias a week or two ago before I got new tubes and it was at .410 and sounded horrible. I’ll let these settle and try to bump it up to .700 and see how it sounds .... I don’t fancy building internal fans etc to keep cool, but i do keep a fan behind it to turn on when it starts to get a bit warm...I noticed soon as I raised the bias it started getting hotter.
     
    Dogs of Doom likes this.
  6. Emtbreid

    Emtbreid Well-Known Member

    Joined:
    Oct 22, 2018
    Messages:
    585
    Likes Received:
    611
    Location:
    East Coast, USA
    I am very proud that I was able to do this on my own more or less with advice from the forum instead Of taking it in and paying someone to do it for me. My local amp ship wanted to charge me $65 just for the power tubes and another $75 for retube, bias, and “checkup”.... I paid $36 for the tubes shipped. And $10 for a multimeter and set of alligator clips ...
     
  7. Dogs of Doom

    Dogs of Doom Moderator Staff Member

    Joined:
    Aug 2, 2012
    Messages:
    20,613
    Likes Received:
    21,412
    Location:
    Los Angeles
  8. Dogs of Doom

    Dogs of Doom Moderator Staff Member

    Joined:
    Aug 2, 2012
    Messages:
    20,613
    Likes Received:
    21,412
    Location:
    Los Angeles
    the probe clips I find work best for the Marshall bias pins, are the spring loaded J-clips:

    EZH633XJL48RB_zpsda247a3b.jpg
     
    mickeydg5 likes this.
  9. Emtbreid

    Emtbreid Well-Known Member

    Joined:
    Oct 22, 2018
    Messages:
    585
    Likes Received:
    611
    Location:
    East Coast, USA
    Ah, I see... that would’ve made things a bit easier. I used alligator clips to hit one of the side pins and the middle ground. Seemed to work ok but this Looks a lot easier..
     
  10. Emtbreid

    Emtbreid Well-Known Member

    Joined:
    Oct 22, 2018
    Messages:
    585
    Likes Received:
    611
    Location:
    East Coast, USA
    Thanks for posting that. I know I’d seen that before. I definitely didn’t let the amp stabilize and sit for half an hour last night before setting that bias (5 mins maybe), so, I took the chassis out again and lo and behold, the bias was all out of whack. So, following his instructions, I set the bias pot low as it could go, and waited 30 minutes. I decided to go a bit above what Marshall states on that bulletin (that I’ve heard may be too cold) and I set it at .650mv (.65mv or 16.25 per el84) to see what that sounds like for a bit.
     
  11. Emtbreid

    Emtbreid Well-Known Member

    Joined:
    Oct 22, 2018
    Messages:
    585
    Likes Received:
    611
    Location:
    East Coast, USA
  12. FourT6and2

    FourT6and2 Active Member

    Joined:
    Dec 3, 2010
    Messages:
    472
    Likes Received:
    242
    Agreed.

    I prefer the sound of a mismatch. If you mismatch too much, it can cause problems. Matched tubes exhibit less noise. But don't sound as nice to me.

    At the end of the day, my amps all have individual bias per tube. So I really don't need to buy matched tubes anyway.
     
  13. JackPlug

    JackPlug New Member

    Joined:
    Sep 1, 2019
    Messages:
    13
    Likes Received:
    16
    back in the old days we never cared about matching and amps didn't break. We simply plugged whatver we had on hand and rarely biased the amps.
    I do like to have them checked and tidied but tube amps seem to be quite forgiving!
     
  14. mickeydg5

    mickeydg5 Well-Known Member

    Joined:
    Sep 30, 2011
    Messages:
    24,027
    Likes Received:
    11,015
    Location:
    US of A
    Yes in the old days they did care.
    I have a stereo amplifier from the 1960's and it tells you to replace with matched tubes that can meet at a specific idle bias within adjustment range of the amplifier.

    Now back then matching tubes may not have been as big a deal and anything under 20% out was considered matching.
    However, I do not agree with the 20% tolerance.
     
  15. john hammond

    john hammond Well-Known Member

    Joined:
    Mar 5, 2019
    Messages:
    952
    Likes Received:
    442
    ironballs, they were most likely cathode biased he's referring to, cathode biased amps you chuck anything in there.

    5e3 tweed deluxe, chuck any 6v6 in there, 250 ohm cathode resistor.
     
  16. mickeydg5

    mickeydg5 Well-Known Member

    Joined:
    Sep 30, 2011
    Messages:
    24,027
    Likes Received:
    11,015
    Location:
    US of A
    But not all tube amplifier's are cathode bias.
     
  17. john hammond

    john hammond Well-Known Member

    Joined:
    Mar 5, 2019
    Messages:
    952
    Likes Received:
    442
    he may be referring to those fender silverface things whereby you just turn a pot to ' balance hum'...did they have fixed adjustable or what? I can of course simply check but its more fun asking
     
  18. mickeydg5

    mickeydg5 Well-Known Member

    Joined:
    Sep 30, 2011
    Messages:
    24,027
    Likes Received:
    11,015
    Location:
    US of A
    What amplifier(s) are you refering to in this post?
     
  19. JackPlug

    JackPlug New Member

    Joined:
    Sep 1, 2019
    Messages:
    13
    Likes Received:
    16
    50W Marshalls, 2204. When a tube went, we simply plugged another one. Little we knew !!
     
  20. mickeydg5

    mickeydg5 Well-Known Member

    Joined:
    Sep 30, 2011
    Messages:
    24,027
    Likes Received:
    11,015
    Location:
    US of A
    Exactly, little you knew.
    It does however make a difference and to a professional or trained ear that is more than too much sometimes.
    A 2204 is served best with matched power tubes.
     
    Last edited: Sep 3, 2019
    JackPlug likes 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