Tube Biasing an Archon 100

Discussion in 'Amplifiers' started by MIke W, Apr 20, 2016.

  1. MIke W

    MIke W New Member

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    Does anyone have the required info for doing this, and internal schematics for the Archon 100?
    Thanks
     
  2. Dusty Chalk

    Dusty Chalk alberngruppenf├╝hrer

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    No schematics, but it's pretty easy -- measure the millivolts across the black and red terminals while turning the single adjustment screw, until it's in the 30 range. Highly recommended to get matching tubes, as there aren't individual bias pots.
     
  3. elvis

    elvis Hamfisted String Banger

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  4. boardn10

    boardn10 New Member

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    Which setting do I use on my multimeter?
    DCV or DCA?
    I think with a bias prob, you measure DCA.
    In this case, should be DCV?
    THANKS!!!
     
  5. Black Plaid

    Black Plaid Other Alan!

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    it's voltage, so DCV == Direct Current Voltage.
     
    #5 Black Plaid, Jul 20, 2021
    Last edited: Jul 20, 2021
  6. RickP

    RickP Established 1960, Still Not Dead

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    Volts. I think that amp has one black and 4 red probe ports (one for each power tube). 30mv is the general rule, though it will not read that on all tubes, even in a matched set. Use the setting that gets you the closest overall across the 4.

    Common (black) stays in the black port, then read each tube by moving your red meter probe through each red port.
     
  7. Em7

    Em7 deus ex machina

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    The amp design uses 1 ohm high precision resistors in series with the power tube cathodes and ground. Using Ohms Law, we know that E (voltage) = I (current) * R (resistance); therefore, thirty milliamps flowing through a 1 ohm resistor results in a 30 millivolt DC voltage drop. It is safer than measuring current directly. To measure current, one would have to insert the meter between the cathodes and ground.
     
  8. dsenoj

    dsenoj Old dude in a PRS T-shirt

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    Seems like a simple and reliable way to measure it. Wonder why most amplifier companies don't do this.
     
  9. boardn10

    boardn10 New Member

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    I spent a lot of time with rolling tube thru the amp, pre and power tubes. I ended up pulling the head out of the shell to see what type of tool I needed for the bias pot. I heard Allen wrench and flat head screw driver. Ended up needing and using a flat head screw driver. I like that there is a wide bias range on this amp. Makes it easier to bias tubes of a wide grade.
    I assume that is what allows it to easily run 6L6 and EL34 tubes. For many amps, it is one or the other, or you have a switch to enable it to bias another tube type.

    Didn't like how the EL34s or E 34Ls sounded as much as 6L6s.
    Also biased up 6CA7 which I love, but still prefer 6L6 in this head. Love my JJ 6L6 GC in this amp biased up to 34-36 mV. Much preferred this over a lower bias. Man, so chewey and rich. It got a little thicker too. I love tube amps biased on the hot side!

    Preamp tubes a I tried a ton and ended up back on the stock JJ tubes. Didn't like any of the others I rolled thru. I tried 5751 in the PI and only slight difference.
    I could EQ/adjust the amp to compensate for anything I didn't like in a preamp tube, for the most part, so I stuck with what sounded and felt best to me.
     
    LSchefman likes this.
  10. LSchefman

    LSchefman Hears Tones

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    If it sounds and feels good, what's not to like?
     
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  11. boardn10

    boardn10 New Member

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    Exactly. The clincher for me was bumping the bias up to 35. It gave it a better feel and thickness.

    I saw a friend gig with the Archon thru a Mesa with V30s. Unreal sounding.
    He had all knobs at 12-1:00.
     
    Alnus Rubra and LSchefman like this.

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