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    550v for MK III KT-88

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    snav

    Posts : 18
    Join date : 2011-05-18

    550v for MK III KT-88

    Post by snav on Mon Jun 06, 2011 12:47 pm

    I was considering an addon PS board with SS rectifiers in place of the 5AR4 or 5U4GB with a delay timer. As I have already found out, the unloaded voltage of the 5U4GB tube rectified transformer can exceed 560v. This amp already runs at about 505v with the 5AR4 so I am not sure what the voltage would be without the tube loss. Anyone that has SS rectifiers care to shed light on this?

    If the SS rectifiers lose much less than the tube what would the effect of a higher supply voltage be on the output tubes and the various intermediate tubes?

    Thanks for any help.


    j beede

    Posts : 316
    Join date : 2011-02-07
    Location : California

    Re: 550v for MK III KT-88

    Post by j beede on Mon Jun 06, 2011 6:40 pm

    I assume that the PS board replaces the 525V quad cap... I think the 6550 is rated for 600V on the plate, 800V for KT-88 and EL-34. I gather from your title that you are running KT-88 so you should be okay there. (Have you compared the sound of your amp running the 6550? Some people and some manufacturers prefer the sound of the 6550).

    I am proponent of eliminating the 525V quad cap, for sure. Why do you want to go with silicon rectification? Have you been going through too many 5AR4? Do you have forward biased 1n400x diodes ahead of your 5AR4 pins 4 and 6? I cannot detect any detrimental effect of adding $1 worth of reliable pre-rectification in front of the relativeley expensive 5AR4.
    ...j

    snav

    Posts : 18
    Join date : 2011-05-18

    Re: 550v for MK III KT-88

    Post by snav on Thu Jun 09, 2011 12:14 am

    I was going to use a replacement cap board to get greater peak voltage margin as well as storage and I'm under the impression that the input capacitance is limited by the tube. So, replacing rectifier as well as capacitors seems appropriate. What I am asking is how the increase would affect the 6AN8 as all the voltages will be higher not just the output pair.


    Last edited by snav on Wed Jun 15, 2011 12:33 am; edited 1 time in total (Reason for editing : Spelling)

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