The Dynaco Tube Audio Forum

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The Dynaco Tube Audio Forum

Dedicated to the restoration and preservation of all original Dynaco tube audio equipment - Customer support for Tubes4hifi VTA tube amp and preamp kits and all Dynakitparts.com products


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    Strange problem, need help

    xlr8
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    xlr8


    Posts : 68
    Join date : 2010-02-09
    • Post n°1

    Strange problem, need help Empty Strange problem, need help

    Post by xlr8 Fri Sep 24, 2010 9:46 am

    Hi folks,

    I came downstairs this morning and fired my st-70s up and one flashed and blew the fuse. I replaced the fuse and turned the amp back on and I get zero bias voltage on all 4 output tubes. All tubes still light up, but there is no sound in either channel and no bias voltage. Please tell me this is something simple. Sad
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    xlr8
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    xlr8


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    Join date : 2010-02-09
    • Post n°2

    Strange problem, need help Empty Re: Strange problem, need help

    Post by xlr8 Fri Sep 24, 2010 9:54 am

    Ok, so I panicked and posted before I tried changing the rectifier. I swapped the newish Sovtek 5AR4 rectum frier with a used Mullard and the amp is working again. Do these modern rectifier tubes really go out within 6 months or should I be looking for another issue?

    Thanks in advance for the help!
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    Bob Latino
    Bob Latino
    Bob Latino
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    Join date : 2008-11-26
    Location : Massachusetts
    • Post n°3

    Strange problem, need help Empty Re: Strange problem, need help

    Post by Bob Latino Fri Sep 24, 2010 11:48 am

    Sad to say that nearly all the newer production GZ34 rectifier tubes are not as "robust" as older USA and British GZ34 rectifier tubes. If you get a year out of most of them, then you are doing OK. Of the newer production GZ34 rectifier tubes (JJ, Sovtek and Ruby), I have had better luck with the Ruby. The Ruby is actually a "select" Chinese GZ34 rectifier tube that has been tested for proper output by Ruby in Califiornia. All Ruby's have the output numbers on a white label on the base of the tube.

    Bob
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    xlr8
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    xlr8


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    • Post n°4

    Strange problem, need help Empty Re: Strange problem, need help

    Post by xlr8 Fri Sep 24, 2010 2:04 pm

    Well, I have been driving mine a little hard lately. I'm thinking I'm just going to go with the Webers, which was my first instinct...I don't want to waste a good Mullard.
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    xlr8
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    xlr8


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    Join date : 2010-02-09
    • Post n°5

    Strange problem, need help Empty Re: Strange problem, need help

    Post by xlr8 Fri Sep 24, 2010 2:16 pm

    All Ruby's have the output numbers on a white label on the base of the tube.

    BTW, I wanted to ask whether these numbers have an effect on the output of the amp? If so, it sort of explains something to me... Embarassed
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    Strange problem, need help Empty Re: Strange problem, need help

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