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    New Tungsol KT120 output tube for Dynaco amps - first impressions on 4/16/10

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    avi.inc

    Posts : 53
    Join date : 2009-08-03
    Age : 63
    Location : L.A.

    Re: New Tungsol KT120 output tube for Dynaco amps - first impressions on 4/16/10

    Post by avi.inc on Tue Nov 02, 2010 2:53 pm

    Thank's Bob

    I have had the amp sens Aug 09 i have the sovtek power tubes in it now and one will not bias. But i have had three quads of the gold lions from guitar center(they ship the tubes with no extra packaging) and they never lasted more than two to three months. I run the amp about 10 to 12 hours a day.I am looking for a good place to get the eight gold lions & four sovtek's tested, seams when they go they like to take the rectifier with it.(I'm getting very good at rebuilding the copper caps). So i ordered kt-120 and I'm hoping that they will last longer. I have a 1951 st-70 that has tubes that are older then me(1953)that plays out in the shop.So I'm wondering how long do the power tubes last on average in a st-120 at reasonable to reasonably loud play? I have Denon avr 3806 as the preamp and crossover 95Hz to sunfire CRM2s as the mains on the st-120.

    Thank's
    Mike B.

    Bob Latino
    Admin

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    Join date : 2008-11-26
    Location : Massachusetts

    Re: New Tungsol KT120 output tube for Dynaco amps - first impressions on 4/16/10

    Post by Bob Latino on Tue Nov 02, 2010 4:12 pm

    Hi Mike,

    Output tubes should last 2000 - 3000 hours on average. Playing 10 - 12 hours a day - that's about 6 months for 2000 hours. It appears that you are getting only 1000 hours or so out of a set of output tubes. It is also possible that the CRM speakers you are using could be presenting a "tough load" to drive and that what is taking out the output tubes. I believe those speakers have a ribbon tweeter. Ribbon tweeters are usually tougher to drive than a conventional tweeter. It is possible that with different speakers you may gain greater tube life ... Just an idea that may or may not be the cause of your shorter than average tube life ..

    Bob

    baddog1946

    Posts : 304
    Join date : 2010-02-03
    Location : Costa Rica

    Re: New Tungsol KT120 output tube for Dynaco amps - first impressions on 4/16/10

    Post by baddog1946 on Sun Nov 07, 2010 6:31 pm

    Hi:
    What diodes are you using to rebuild the copper caps if you changed them or did you just change the resistors and are you replacing the thermistor as well?
    I rebuilt a WX68 and changed all the parts but used the stock parts values and it seems to be fine. I am wondering which parts are prone to failure. Of course the resistors were fried but I wonder if some of the other parts are also damaged when they blow? Is it possible to change the resistor value for a little more durability.

    avi.inc

    Posts : 53
    Join date : 2009-08-03
    Age : 63
    Location : L.A.

    Re: New Tungsol KT120 output tube for Dynaco amps - first impressions on 4/16/10

    Post by avi.inc on Sun Nov 07, 2010 9:50 pm

    I have rebuilt one four time's with only the resistors needing to be replaced.

    baddog1946

    Posts : 304
    Join date : 2010-02-03
    Location : Costa Rica

    Re: New Tungsol KT120 output tube for Dynaco amps - first impressions on 4/16/10

    Post by baddog1946 on Mon Nov 08, 2010 8:10 am

    Hi Avi:
    That's kind of my point you had to build it 4 times. I am thinking that the diodes are a little fried. Mine is still working after 6 months. Diodes can be damaged by heat and those things get quite hot. Still there are a lot of other things that can blow them.
    Baddog1946

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