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Thread: I am about to try to bias my UL myself - HELP!

  1. #1
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    Default I am about to try to bias my UL myself - HELP! (PICTURES INSIDE)

    I just bought a matched quad of KT88EH's from Doug at www.Dougstubes.com and I want to replace the tubes that I have in there and bias them. I have a Weber Biasrite with the V1 option. The old tubes in there are Sovtek's but the VHT logo is silk screened on them. On each VHT tube at the bottom of the metal base is written 128 on each.

    See picture:
    Last edited by rbone100; 04-28-2005 at 08:51 AM.
    www.myspace.com/rbone100
    My bands website: www.sugarbuzzband.com
    Picture site: www.guitarfan.com
    CLX head, UL head, CLX 2x12 Combo, Pittbull 45 Combo, VHT 4x12 with P50E's

  2. #2
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    Here are some pics inside of the amp:
    www.myspace.com/rbone100
    My bands website: www.sugarbuzzband.com
    Picture site: www.guitarfan.com
    CLX head, UL head, CLX 2x12 Combo, Pittbull 45 Combo, VHT 4x12 with P50E's

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    From careful examination on the inside I believe that this hole with the screw inside is where I would bias the amp? It is labeled BIAS on the board.

    See picture:
    www.myspace.com/rbone100
    My bands website: www.sugarbuzzband.com
    Picture site: www.guitarfan.com
    CLX head, UL head, CLX 2x12 Combo, Pittbull 45 Combo, VHT 4x12 with P50E's

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    Before I do anything else, I am going to hook up the Weber Biasrite and get some readings with the tubes that are currently in there and I will post back.
    www.myspace.com/rbone100
    My bands website: www.sugarbuzzband.com
    Picture site: www.guitarfan.com
    CLX head, UL head, CLX 2x12 Combo, Pittbull 45 Combo, VHT 4x12 with P50E's

  5. #5
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    Quote Originally Posted by rbone100
    From careful examination on the inside I believe that this hole with the screw inside is where I would bias the amp? It is labeled BIAS on the board.

    See picture:
    Hey, be careful there rbone!!! Don't wanna fry that amp! Why dontcha call VHT first?

    brian
    "If you're ain't playin' a VHT amp yet, well...you better go 'n git one raht now!

  6. #6
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    Ok... I hooked up the Biasrite and this is what it looks like hooked up to the amp. I connected the speaker jack to my cabinet and powered it up and let it warm up. I then took the standby off and got each plate voltage reading--V1 option?
    www.myspace.com/rbone100
    My bands website: www.sugarbuzzband.com
    Picture site: www.guitarfan.com
    CLX head, UL head, CLX 2x12 Combo, Pittbull 45 Combo, VHT 4x12 with P50E's

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    Here is the plate voltage reading for each KT88 (A - D) that came with the amp. The "A" tube is the left most tube in the picture above--Picture P1020039 is the "A."

    See pics
    www.myspace.com/rbone100
    My bands website: www.sugarbuzzband.com
    Picture site: www.guitarfan.com
    CLX head, UL head, CLX 2x12 Combo, Pittbull 45 Combo, VHT 4x12 with P50E's

  8. #8
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    Here is the individual voltage reading for each KT88 (A - D) that came with the amp. The "A" tube is the left most tube in the picture above--Picture P1020043 is the "A" tube. As you can see by the readings that the tubes aren't all the same reading. Either the amp wasn't biased properly or (My guess) a matched set of tubes were not used?

    See pics
    www.myspace.com/rbone100
    My bands website: www.sugarbuzzband.com
    Picture site: www.guitarfan.com
    CLX head, UL head, CLX 2x12 Combo, Pittbull 45 Combo, VHT 4x12 with P50E's

  9. #9
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    Here is a recap on the Biasrite readings:

    Individual plate voltage (V option) readings:

    A-458
    B-464
    C-485
    D-473

    Individual bias readings:

    A-51.1
    B-58.0
    C-51.2
    D-54.4

    That is all that I am doing tonight. Hopefully I will I hear from some members of the forum that have done this before and can point me in the right direction.

    Ralphie
    Last edited by rbone100; 04-27-2005 at 11:08 PM.
    www.myspace.com/rbone100
    My bands website: www.sugarbuzzband.com
    Picture site: www.guitarfan.com
    CLX head, UL head, CLX 2x12 Combo, Pittbull 45 Combo, VHT 4x12 with P50E's

  10. Default

    It is strange IMHO that you got different voltage readings; usually they are all the same across. That might be a question to ask VHT.

    Here is a link to find the safe range of settings to use when biasing the amp:

    http://www.webervst.com/tubes/calcbias.htm

    Remember to use your ears; but keep it in the safe range for the tube you are using.

    Use a flashlight to look down into the hole and look for one of those tiny pots that you have to use a micro-screwdriver on; that will be the bias pot. On my VHT 50/ST the pot is not marked at all.
    -- Scott Peterson

    www.spetersonmusic.com

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