Weber Bias Rite with V1

Discussion in 'Amps and Cabs' started by Red Planet, Dec 29, 2005.

  1. Red Planet

    Red Planet Member

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    Got a chance to use this thing finally. According to the Math it should come out at 39ma but all I can get is 33 on one set and 31 on the other set of EL34's in my JCM 800 2203.

    I think Doug R had mentioned before about not going over 35ma ever with an EL34 but how do you explain that with the Math?

    The most I can get with the Bias Pot Full up is 33.4

    This is all new to me so I'm trying to be cautious.

    Anyone have any thoughts on this subject.

    Now bear in mind I'm using Bias Probes not a Scope.
     
  2. aleclee

    aleclee TGP Tech Wrangler Staff Member

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    If it sounds good at that bias, I wouldn't worry about it. 70% is a max but not necessarily where you want things biased. Many of us find that much cooler biasing doesn't sacrifice tone while extending tube life.
     
  3. Argonaut4

    Argonaut4 Member

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    Are you figuring 70% of dissipation? If so, I think you're just fine with the readings you're getting. I usually bias my amps somewhere between 60 and 70%. Usually closer to 60%. I like to use the probe to get it close and then use my ears to fine tune.

    If you want to bias it hotter, you'll either have to try some different tubes or change a resistor.

    Good luck!

    J
     
  4. Scott Peterson

    Scott Peterson Staff Member

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    What both Alec and Argonaut4 say.

    On EL-34's, up in the mid thirties is VERY hot. I tend to set my amps with EL34's a bit cooler, at 29ma or so. But that also sounds best to me.
     
  5. jdzialak

    jdzialak Silver Supporting Member

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    A very well known Marshall amp guy just told me - forget the Math, set it at 30ma and be done with it.

    Joe
     
  6. sundaypunch

    sundaypunch Member

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    It all depends on your plate voltage. You have the V1 option so you should be able to measure this. If you are pushing 500V then 30mA plate dissipation would be 60% which should be plenty conservative. I use the charts on this website for a reference-

    http://members.shaw.ca/house-of-jim/Html/bias_tables.html
     
  7. Red Planet

    Red Planet Member

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    Thanx for the replys guys. I'm new to this so bare with me here.

    My Plate Voltage was 440 and I'm going on 70% and come up with 39ma.

    What I'm freaking confused about is the Math -- on the one hand to get the correct amount you calculate and on the other that aint right.

    So the only difference between the two is the slightly lower Cathode Current allows the Tubes to last longer?
     
  8. Red Planet

    Red Planet Member

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    Thanx for the link Sundaypunch. That will save my calculator from overheating.

    I nticed he said in a note at the top of the page that these figure were based on NOS Tube Performance and with Modern Day Tube one might want to be even more conservative than 50 percent.

    I'm gonna play with it a little and see what I think about the differences.

    Another question I have is say from Left to Right Tube One Biased at 33 and Two at 31 and Three at 31 and Four at 33. Is it the Tubes that are making this difference in numbers or the Circuit. If I take the #1 and #2 Tubes and switch them will it Balace things out more and will I notice a difference in the sound and would it be better?

    So is the general consensous that one should Bias a little cool to make the Tubes last longer and because of using Modern Production Tubes?

    Any Info anyone wants to stick in please do.
     
  9. Red Planet

    Red Planet Member

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    And also would the wattage figures be right for Modern Tubes?
     
  10. bluessyndicate

    bluessyndicate Member

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    I used to set my Shiva EL34 at 30-31 ma using a Bias Rite with V1. That's a handy little tool. Too bad I don't need one anymore, since my amps have biasing ports....
     
  11. sundaypunch

    sundaypunch Member

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    I guess the thinking is that modern tubes can't handle what many old ones could. I have a Traynor YBA-1 that has plate voltages way over 500V. I have been told that any new tube would have a very short lifespan. I would definitely run them cool if I was using a new tube.

    If you are running at 440V I don't think that is a problem for new tubes. You might let one of the experts chime in though.
     
  12. thelionsden

    thelionsden Member

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    tubes one and four work together to make a pair and tubes 2 and 3 make a pair so you are right on. Within a couple numbers like you are throughout is very closely matched, I wouldn't worry about it.
     

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