The Dynaco Tube Audio Forum

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


    Ultimate PAS upgrade and 12x4

    Share

    Dingojazz

    Posts : 68
    Join date : 2010-09-03

    Ultimate PAS upgrade and 12x4

    Post by Dingojazz on Fri Nov 02, 2018 9:56 am

    Would the beefed-up power supply of the VTA "Ultimate" PAS upgrade affect the operation/lifespan of the 12x4 rectifier?
    I did the upgrade a few years back, and when the pre started misbehaving recently, it 'ultimately' turned out to be the 12x4, a NOS RCA which replaced the original Dynaco stamped tube .

    Since these are supposed to have a long span (like, forever), I wondered if the 'Ultimate' might have created more challenging operating conditions Rolling Eyes.
    If not, is there somewhere else to look for clues?

    Any help appreciated,

    K.
    avatar
    peterh

    Posts : 1054
    Join date : 2012-12-25
    Location : gothenburg, sweden

    Re: Ultimate PAS upgrade and 12x4

    Post by peterh on Fri Nov 02, 2018 10:19 am

    Dingojazz wrote:Would the beefed-up power supply of the VTA "Ultimate" PAS upgrade affect the operation/lifespan of the 12x4 rectifier?
    I did the upgrade a few years back, and when the pre started misbehaving recently, it 'ultimately' turned out to be the 12x4, a NOS RCA which replaced the original Dynaco stamped tube .

    Since these are supposed to have a long span (like, forever), I wondered if the 'Ultimate' might have created more challenging operating conditions :roll:.
    If not, is there somewhere else to look for clues?

    Any help appreciated,

    K.
    I have no idea of what a "Ultimate" PAS upgrade " consists of. But i know that 12x4
    will easily be replaced by 2 1n4007 or un4007 Si diodes. Some upgrade boards even has
    place for these diodes, if your does not, a minimal 2 pole lug will be all you need.
    Your power transformer will thank you for reducing the load.
    avatar
    erhard-audio

    Posts : 40
    Join date : 2017-04-07
    Age : 60
    Location : Tucson, AZ

    Re: Ultimate PAS upgrade and 12x4

    Post by erhard-audio on Fri Nov 02, 2018 10:32 am

    Are you referring to the PAS upgrade kits formerly sold by Tubes4HiFi and now by us? If yes, then there is really no difference between the kit and the original Dynaco as far as the 12X4 side of the circuit is concerned. The main difference is the transformer used for B+ by the kit, which is a higher capacity than the original PA211 and the addition of the two diodes at the base of the 12X4 socket to 'create a center tap'.
    Downstream of the 12X4 is a high voltage regulator based on the LR8 for B+. In fact, I would go as far as saying that the kit circuit presents less operating stress on the 12X4 than the original Dynaco circuit.
    No tube lasts forever, so it could very well have simply be a 'worn out' 12X4 or it just simply went faulty.

    Dingojazz

    Posts : 68
    Join date : 2010-09-03

    Yes, it would be 'that' upgrade kit

    Post by Dingojazz on Fri Nov 02, 2018 11:09 am


    so in that case, it sounds like the changes to the operating conditions would be minimal...
    We'll replace the 12x4 and see how she goes.

    Thanks for the helpful responses,

    K.

    Sponsored content

    Re: Ultimate PAS upgrade and 12x4

    Post by Sponsored content


      Current date/time is Tue Nov 13, 2018 9:39 pm