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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 products

    Power Tube Life


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    Join date : 2011-10-06

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    Post by Heaviside on Wed Oct 19, 2011 10:59 am

    Hi all,

    I have provided a link to an article published in 2005 by David Gillespie. He advocates the inclusion of screen resistors to improve stability and reduce arcing. He also advocates delaying B+ application.

    Let me know what you think.



    Gillespie Article

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    Post by GP49 on Wed Oct 19, 2011 11:14 am

    After trying out one of my modified Mark II (with greatly increased power supply reservoir storage) in triode mode, I left the added resistors in there and used them as screen grid resistors as suggested by Gillespie and others, although I had had zero problems with output tubes arcing. I can't detect any deterioration in performance by doing so; if there is a safety margin thus introduced, I'd have to say it comes for no cost (well, for a few cents that the resistors cost) and for very little effort.

    The other modified Mark II has not received the screen grid resistors. But as mentioned, I've not had any tube arcing in either one.

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    Power Tube Life Empty Delay B+

    Post by zx on Wed Oct 19, 2011 11:24 am

    He also advocates delaying B+ application.

    The way i get the B+ delay in the Dynaco MK3s is to put a swetch in the B+ center tap,this is a ezy way to get the heaters on an then add the B+.
    Thanks for the post

    Thanks Bob for the site
    Bob Latino
    Bob Latino

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    Post by Bob Latino on Wed Oct 19, 2011 12:20 pm

    Just to be clear about delaying the B+ voltage on the original Dynaco amps and/or the VTA amp kits ... If you use a GZ34 TUBE rectifier, you don't really need any B+ delay switch, board etc. A GZ34 tube rectifier has an indirectly heated filament which warms up slowly. (maybe 15 to 20 seconds ..) This indirectly heated filament acts as a B+ delay and, as such, no switch/delay board/relay etc. is needed if you use a GZ34 tube rectifier. If you use a SOLID STATE rectifier, then it may be useful to delay the B+ high voltage on your amp. The Weber WZ68 does have a short 3 to 5 second built in delay before full B+ is applied. This short delay is (apparently) enough. I have used the same Weber WZ68 SS rectifier in my own ST-120 for over a year now with no issues.


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