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    Valve Art KT66 Tubes Heavy Load

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    Ed Cheek

    Posts : 6
    Join date : 2013-02-10

    Valve Art KT66 Tubes Heavy Load

    Post by Ed Cheek on Thu Apr 11, 2013 9:43 pm

    Hello all,

    I purchased a quad of Valve Art KT66 tubes and installed them into my VTA ST70 today. I have been running Gold Lion KT66 tubes which I like very much. I wanted to compare to the Chinese tubes. I switched off my amp after an hour of playing the stereo and I noticed that the power transformer was HOT. I biased them at .45mA. The Gold Lion tubes never loaded the transformer that much. The transformer was just warm to the touch before with the Gold Lion tubes.

    I did notice that when I switched off power that the filaments took 15-20 seconds to loose all of their glow. The manufacturer must have used some heavy tungsten.

    Has anyone any experience with these tubes? I am not sure if this is normal for these tubes or if I got a bum set. I do not plan to use them again and risk burning up my power transformer.

    Thanks in advance.

    Ed Cheek

    Bob Latino
    Admin

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

    Re: Valve Art KT66 Tubes Heavy Load

    Post by Bob Latino on Fri Apr 12, 2013 10:04 am

    Hi Ed,

    Some output tubes do draw more current than others - even some of the same type .. EL34, KT66 etc. The power transformer on the VTA ST-70 will allow you to run KT88's in a VTA ST-70 (do NOT run KT88's in an original Dynaco ST-70 with the original PA-060 power transformer). KT88's draw more current than a KT66. You can run the Valve Art KT66's in any VTA ST-70. The power transformer may run a little warmer but you will not harm the power transformer in the VTA ST-70 amp.

    Bob

    Jim McShane

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

    Re: Valve Art KT66 Tubes Heavy Load

    Post by Jim McShane on Fri Apr 12, 2013 4:36 pm

    Bob Latino wrote:The power transformer may run a little warmer but you will not harm the power transformer in the VTA ST-70 amp.
    To add to what Bob said - keep in mind too that what is "hot" to you and I is not hot at all to a quality transformer. If you can hold your hand on the trafo for even a few seconds it means the temperature is at or below about 130 degrees F - that's a piece of cake for a good trafo. They can take much more. Even cheapie trafos can usually take 185 degrees F or so, and the trafo Bob's amps use is not a cheapie, it's a good quality piece.

    wildiowa

    Posts : 120
    Join date : 2012-03-19

    Re: Valve Art KT66 Tubes Heavy Load

    Post by wildiowa on Fri Apr 12, 2013 5:12 pm

    I have a Cit II with the McShane mods and the transformers run quite hot with 6550s. If it is on for a few hours it really gets cooking, can't really hold your hand on them after a few seconds especially power trans. I am not a tech and worried a bit at first but it is OK and those transformers are huge so I guess the designers knew what they were doing.

    Jim McShane

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

    Re: Valve Art KT66 Tubes Heavy Load

    Post by Jim McShane on Fri Apr 12, 2013 5:27 pm

    wildiowa wrote:I have a Cit II with the McShane mods and the transformers run quite hot with 6550s. If it is on for a few hours it really gets cooking, can't really hold your hand on them after a few seconds especially power trans. I am not a tech and worried a bit at first but it is OK and those transformers are huge so I guess the designers knew what they were doing.
    Much of the heat is radiated from the power tubes which are very close by, it's not all generated by the trafos themselves.

    Also, as you said - you can only hold your hand on the transformer case for a few seconds. That means they are about 130 F, not even warm enough to break a sweat for them! That may be hot to you, but to a quality transformer it's cool as a cucumber!

    Ed Cheek

    Posts : 6
    Join date : 2013-02-10

    Many Thanks

    Post by Ed Cheek on Fri Apr 12, 2013 7:09 pm

    Thanks to all of you for your helpful answers. I appreciate your time and experience. Hopefully I can return the favor someday. I will continue to use the KT-66 tubes. I wish a good weekend to all.

    j beede

    Posts : 317
    Join date : 2011-02-07
    Location : California

    Re: Valve Art KT66 Tubes Heavy Load

    Post by j beede on Sat Apr 13, 2013 12:09 am

    Why not get yourself a basic IR contactless thermometer. I find it to be a useful tool. Harbor Freight has one that goes on sale for less than $10 every now and again. Look here.

    http://www.harborfreight.com/non-contact-pocket-thermometer-93983.html

    tubes4hifi
    Admin

    Posts : 1261
    Join date : 2008-11-30

    Re: Valve Art KT66 Tubes Heavy Load

    Post by tubes4hifi on Sat Apr 13, 2013 8:37 pm

    dang, I paid $25 for this one, but it has a 6:1 ratio on the measuring area, VS 1:1 on the cheap one.
    So from 6" I get a 1" read area, rather than a 6" circle area on cheaper one, so worth the extra $$
    http://www.harborfreight.com/infrared-thermometer-93984.html
    Not a problem if you're measuring a tube from 1" away.
    As long as you're there, get a couple of these for measuring tube bias. I've got 4 of them now, real handy!
    http://www.harborfreight.com/7-function-multimeter-98025.html

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