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    Genalex Gold Lion Bias Adjustment

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    MontanaWay

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    Re: Genalex Gold Lion Bias Adjustment

    Post by MontanaWay on Wed Jul 01, 2015 10:17 am

    here here...I totally agree. Although not a huge amount, but I do buy tubes from Jim for some of my builds and have never had an issue, in fact, they have all been outstanding!
    I guess some people just seem to get a bee under their bonnet, on no matter what, there is no way to remove that bee!! scratch
    On the very positive side, and I am speaking from my own experiences as well, 99.9% of people we deal with WAY outweigh that 0.1% who just cannot be pleased.

    tubes4hifi
    Admin

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    Re: Genalex Gold Lion Bias Adjustment

    Post by tubes4hifi on Wed Jul 01, 2015 12:08 pm

    I feel compelled to add my response here . . . Hooray to Jim McShane for going above and beyond on replacing questionable tubes, even when the problem isn't the tube.
    I just read his old FAQ and agree with the whole thing, and I agree with him that I get the same questions over and over and over and over.
    5-10 years ago we didn't have this problem. People with tube amps were both electronics enthusiasts and audio enthusiasts. Now 90% of them don't know anything about electronics, and unfortunately that a huge negative problem if you want to have a good experience with a tube amplifier.
    99% of the time, tubes go bad for one of two reasons
    1-operator error (incorrect or no bias adjustment, turning the wrong pot, turning it the wrong way, not knowing how to use a meter, etc.)
    2- loose tube socket pins
    1% of the time it's just poor quality control and especially because in these modern times, tubes aren't made the way the were 50 years ago.
    50 years ago, tubes were all hand-made and hand tested, and they were built to last forever. These days, tubes are a commodity, made by someone who
    purchased a license and some old equipment from someone who went out of business, to make a quick profit, and too bad if they don't make it thru a 90 day warranty!
    Even just a couple years ago, I purchased 4 new EH tubes (now I hate to say EH tubes are bad, they aren't, but you get what you pay for, and they are OK for the money).
    Four new KT88s. 3 of them wouldn't work in my ST70 amp. Runaway bias. The cure for runaway bias I've found to be lowering the grid resistance to ground.
    Used to be 270K was fine, then it was 220K. I haven't found an EH KT88 yet that will hold bias unless that resistance is only 150K or less, so for the past 3 years all the VTA70 kits I sent out now use 150K grid resistors to ground. I've heard many people on other forums recommending that change to 100K.
    I've never tried a KT120 but I see Jim's FAQ states that it wants LESS than 51K. That's simply unbelievable (well, not really, but it's kind of ridiculous, since I've never seen any tube amp use less than 100K).
    So Bob, if you're reading this, I'd recommend you make a 100K resistor standard in all your bigger amps (especially the M125s) and add a note that if you're going to try using KT120s to change that to a 51K resistor.
    I think 90% plus of the people on this forum are very well educated, now that they have this experience with tube amps.
    But for newbies - take note!! At least learn how to use a meter, understand tube bias, and make sure the tube fits tight in the socket pins.
    THEN - enjoy the music!!

    Bob Latino
    Admin

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    Location : Massachusetts

    Re: Genalex Gold Lion Bias Adjustment

    Post by Bob Latino on Wed Jul 01, 2015 1:50 pm

    tubes4hifi wrote:
    So Bob, if you're reading this, I'd recommend you make a 100K resistor standard in all your bigger amps (especially the M125s) and add a note

    The VTA ST-120 has always shipped with 150K grid resistors and the VTA M-125's always ship with 100K grid resistors. In the VTA ST-70 the 270K grid resistors seem to work fine with EL34 or 6L6 type tubes. If a customer wants to use 6550 or KT88 output tubes in their ST-70 kit, I usually ship the amp with 150K grid resistors ..

    I agree with Roy on customer biasing problems... Meter on AC instead of DC when measuring bias, meter set to the wrong DC scale, auto ranging meters that do not in fact "auto range", placing the red probe in the wrong front pin socket etc. errors .. In all the VTA amp kit manuals the biasing procedure is outlined in detail BUT - people (sometimes) do not read the manual and do not follow the procedure properly ..

    Also - If you are a "tube jockey" and like to cycle different brand or type of output tubes in and out of your amp, you may run into a non biasing situation if the newer tubes you just put in have pins that are even 1/1000 of an inch smaller. If you lose contact on pin #3 or #5, you won't have any bias. Before you complain to Jim McShane about the tubes that he sent to you, see if the tube that won't bias WILL BIAS in another socket. If it will, it is nearly always a pin contact issue. Try retensioning the octal pins. Use a small flat edge jewelers screwdriver from the top of the amp to push together the two sides of all the socket pins just a little. This will usually do the trick ..

    Bob

    Jim McShane

    Posts : 154
    Join date : 2011-10-19
    Location : South Suburban Chicago

    Re: Genalex Gold Lion Bias Adjustment

    Post by Jim McShane on Wed Jul 01, 2015 2:23 pm

    Bob Latino wrote:
    tubes4hifi wrote:
    So Bob, if you're reading this, I'd recommend you make a 100K resistor standard in all your bigger amps (especially the M125s) and add a note

    The VTA ST-120 has always shipped with 150K grid resistors and the VTA M-125's always ship with 100K grid resistors. In the VTA ST-70 the 270K grid resistors seem to work fine with EL34 or 6L6 type tubes. If a customer wants to use 6550 or KT88 output tubes in their ST-70 kit, I usually ship the amp with 150K grid resistors ..

    I agree with Roy on customer biasing problems... Meter on AC instead of DC when measuring bias, meter set to the wrong DC scale, auto ranging meters that do not in fact "auto range", placing the red probe in the wrong front pin socket etc. errors .. In all the VTA amp kit manuals the biasing procedure is outlined in detail BUT - people (sometimes) do not read the manual and do not follow the procedure properly ..

    Also - If you are a "tube jockey" and like to cycle different brand or type of output tubes in and out of your amp, you may run into a non biasing situation if the newer tubes you just put in have pins that are even 1/1000 of an inch smaller. If you lose contact on pin #3 or #5, you won't have any bias. Before you complain to Jim McShane about the tubes that he sent to you, see if the tube that won't bias WILL BIAS in another socket. If it will, it is nearly always a pin contact issue. Try retensioning the octal pins. Use a small flat edge jewelers screwdriver from the top of the amp to push together the two sides of all the socket pins just a little. This will usually do the trick ..

    Bob


    Hi Bob,

    The 51K number is the spec that is published by New Sensor for fixed bias circuits and KT-120s. If anyone would like to see the whole spec sheet look here: http://www.newsensor.com/TubeSpecification.aspx Click on the Tung-Sol drop down menu and select the KT-120. You'll get a .pdf you can view or save.

    I have not heard of any issues with higher values, but just so everyone knows - that's the "official" word.

    Bob Latino
    Admin

    Posts : 2378
    Join date : 2008-11-26
    Location : Massachusetts

    Re: Genalex Gold Lion Bias Adjustment

    Post by Bob Latino on Wed Jul 01, 2015 2:37 pm

    Hi Jim,

    No one has reported any issues using 100K grid resistors with the M-125's ..

    NOTE - I am going to lock this thread .. there is no sense in going back and forth again and again over whether the tube or the "pilot" of the amp is at fault ..

    Bob

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