The Dynaco Tube Audio Forum

Would you like to react to this message? Create an account in a few clicks or log in to continue.
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


2 posters

    Strange problem, need help

    avatar
    xlr8


    Posts : 68
    Join date : 2010-02-09

    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
    avatar
    xlr8


    Posts : 68
    Join date : 2010-02-09

    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!
    Bob Latino
    Bob Latino
    Admin


    Posts : 3260
    Join date : 2008-11-26
    Location : Massachusetts

    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
    avatar
    xlr8


    Posts : 68
    Join date : 2010-02-09

    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.
    avatar
    xlr8


    Posts : 68
    Join date : 2010-02-09

    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

    Sponsored content


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

    Post by Sponsored content


      Current date/time is Fri Mar 29, 2024 4:46 am