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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 Dynakitparts.com products


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    6550, KT88 and EH 6CA7 in ST70

    hrudu90
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    hrudu90


    Posts : 27
    Join date : 2011-01-02
    • Post n°1

    6550, KT88 and EH 6CA7 in ST70 Empty 6550, KT88 and EH 6CA7 in ST70

    Post by hrudu90 Wed Jul 25, 2012 1:24 pm

    I am wondering if it is possible to use the 6550's and KT88's in the VTA-ST70
    without any modifications? Just bias them correctly?

    BTW, I found some nice EH 6CA7's on tubes4hifi.com website; and they can be used
    without any modifications as well? Treat them just like the EL34's?



    ~~~
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    Bob Latino
    Bob Latino
    Bob Latino
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    Posts : 3263
    Join date : 2008-11-26
    Location : Massachusetts
    • Post n°2

    6550, KT88 and EH 6CA7 in ST70 Empty Re: 6550, KT88 and EH 6CA7 in ST70

    Post by Bob Latino Wed Jul 25, 2012 2:29 pm

    Yes - KT88 or 6550 tubes may be used in the VTA ST-70. Just plug them in and bias them at .500 VDC per each output tube. Do not use 6550 or KT88 output tubes in any ORIGINAL ST-70. The VTA ST-70 kit has a beefed up power transformer and can handle the extra current draw of 6550 or KT88 output tubes. The power transformer on the original ST-70 was undersized and runs fairly warm just with the smaller EL34 output tubes.

    Yes - Treat any 6CA7 as an EL34 and bias them at .400 VDC per each output tube in a VTA ST-70.

    Bob
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