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    KT66 matching quad

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    pjp3

    Posts : 39
    Join date : 2013-03-19
    Age : 54
    Location : Pelham, AL

    KT66 matching quad

    Post by pjp3 on Sun Jul 07, 2013 12:47 am

    I bought a matching quad of GL KT66 tubes and love the expansive sound stage. But, unfortunately, I dropped one of the tubes
    and it shattered. So, I ordered another tube to fill in the set. All is well for for about 40 hours when the new tube burns up inside,
    the entire tube is red and glowing inside. Burns up... Is this because I no longer have a matched quad? The bias settled in early and I checked it regularly,
    when the tube was turned red the reading was 3.88 instead of .50. Doh! Shouldn't the ability of independent bias control eliminate the need for
    matched tubes?

    peterh

    Posts : 679
    Join date : 2012-12-25
    Location : gothenburg, sweden

    Re: KT66 matching quad

    Post by peterh on Sun Jul 07, 2013 4:01 am

    pjp3 wrote:I bought a matching quad of GL KT66 tubes and love the expansive sound stage. But, unfortunately, I dropped one of the tubes
    and it shattered. So, I ordered another tube to fill in the set. All is well for for about 40 hours when the new tube burns up inside,
    the entire tube is red and glowing inside. Burns up... Is this because I no longer have a matched quad? The bias settled in early and I checked it regularly,
    when the tube was turned red the reading was 3.88 instead of .50. Doh! Shouldn't the ability of independent bias control eliminate the need for
    matched tubes?
    You could have ordered a matched pair. The tubes i sell has been marked with characteristica so if one breaks i can send a matching mate.

    Individual bias does not help if the tubes has differing Gm.

    Bob Latino
    Admin

    Posts : 2411
    Join date : 2008-11-26
    Location : Massachusetts

    Re: KT66 matching quad

    Post by Bob Latino on Sun Jul 07, 2013 7:36 am

    Hi,

    The VTA board's ability to bias tube does allow you to use output tubes that are not pefectly matched. I don't think that the "matching tube issue" is the cause of you losing another tube. I have two thoughts here ..

    1. It was just a freaky, chancy thing that cause you to lose another tube even though this tube was near new. Try ANOTHER KT66 in there. If another KT66 fails in that same socket then it is probably # 2 below.

    2. There is some issue on that tube socket OR on the part of the driver board that feeds that tube that is not right. Maybe a bad solder connection that after many heat up and cool down cycles just gave way? Maybe one of the pins on that tube socket is not gripping the tube pins properly. A leaky capacitor ?

    Bob

    sKiZo

    Posts : 1310
    Join date : 2013-04-01
    Location : Michigan USA

    Re: KT66 matching quad

    Post by sKiZo on Sun Jul 07, 2013 4:49 pm

    Reminds me of when I got my TungSol KT-120's. They had these big blue and white stickers on the bases to reference the match number. Couldn't see having those on those beautiful chrome bases, but couldn't peel them off without tearing them.

    Got hold of the seller with a question "How do I get your silly stickers off your tubes?"
    To which their response was "we don't have silly stickers."
    To which my response was "How do I get your stickers off your silly tubes?" tongue 

    (A blow drier does the job. Just heat the sticker and they peel right off. I saved one for the bottom of the cabinet.)

    Anyway ... I'd expect the fried tube was just a fluke. They don't give them much of a burn in, so cross your fingers and get another one.

    sKiZo

    Posts : 1310
    Join date : 2013-04-01
    Location : Michigan USA

    Re: KT66 matching quad

    Post by sKiZo on Sun Jul 07, 2013 4:53 pm

    Bob Latino wrote:

    The VTA board's ability to bias tube does allow you to use output tubes that are not pefectly matched.

    Bit of a derail, but just what IS the adjustment range of the VTA board bias adjusters? Reason I ask is I plan to replace the on board controls with some 50K pots on my custom build and was wondering how much damage I could do if I were to like ... er ... wire them up backwards.

    Yeah. I know. The correct answer is "don't do that". But hey, I'm Polish. jocolor

    peterh

    Posts : 679
    Join date : 2012-12-25
    Location : gothenburg, sweden

    Re: KT66 matching quad

    Post by peterh on Mon Jul 08, 2013 6:40 am

    sKiZo wrote:Reminds me of when I got my TungSol KT-120's. They had these big blue and white stickers on the bases to reference the match number. Couldn't see having those on those beautiful chrome bases, but couldn't peel them off without tearing them.

    Got hold of the seller with a question "How do I get your silly stickers off your tubes?"
    To which their response was "we don't have silly stickers."
    To which my response was "How do I get your stickers off your silly tubes?" tongue 

    (A blow drier does the job. Just heat the sticker and they peel right off. I saved one for the bottom of the cabinet.)

    Anyway ... I'd expect the fried tube was just a fluke. They don't give them much of a burn in, so cross your fingers and get another one.

    The point with the stickers you mentioned and the ones i label tubes i sell is to be able to get a replacement tube with identical characteristics. Of course the tubes ages, then the label is of less value. But at the beginning of
    the tubes life there is also the largest risk of failure, during this period ( up to 3-6 month ) a tube can successfully be replaced with i new with identical values.

    If one starts with matched pair ( or quads) there is no point at all to replace one of them with a random chosen one if there is information ( and the seller can deliver) an identical tube.


    pjp3

    Posts : 39
    Join date : 2013-03-19
    Age : 54
    Location : Pelham, AL

    Re: KT66 matching quad

    Post by pjp3 on Mon Jul 08, 2013 10:14 am

    Bob, I have actually had two spares burn out in two different locations. One was left back, the latest
    was the front right. I have a new quad on the the way, so if anyone needs three gently used GL
    KT66's...

    Peterh, I will note the sticker this time instead of removing and discarding:0

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