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    Dynaco Mark III Rectifier Tube Question


    Posts : 1
    Join date : 2013-01-26
    Location : Canada

    Dynaco Mark III Rectifier Tube Question

    Post by RossVintageRadio on Sat Jan 26, 2013 6:45 pm

    Hello to All,

    I have just acquired at pair of the Dynaco Mark III Mono Blocks.

    I see that one has the correct 5AR4 Rectifier tube.....but the other one has a 5U4GB tube in it.

    Both have 6550's for Outputs.

    I realize that the 5AR4 is the correct rectifier, and I wonder if the 5U4 was tossed in so the one amp would function.

    Both amps also have the SDS Capacitor Boards installed.

    I want to run a Quad of KT-88's in them....and I will replace the 5U4 Tube with a 5AR4 Tube and then just Re bias Both amps

    Just wondered if my thoughts are right as to why there is a 5U4 Rectifier in the 1 amp?

    Thank You
    Bob Latino

    Posts : 2648
    Join date : 2008-11-26
    Location : Massachusetts

    Re: Dynaco Mark III Rectifier Tube Question

    Post by Bob Latino on Sat Jan 26, 2013 8:25 pm

    The 5U4 WAS probably tossed in so that the amp would work. A 5U4 has a higher voltage drop than a GZ34. The amp with the 5U4 will have a lower B+ voltage and consequently a little less power than the other amp. Get a GZ34 for that amp that now has the 5U4 and keep the 5U4 as a spare rectifier to be used in an emergency to keep the music going in case one of the other rectifiers goes bad.


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