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

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Dynaco Mark III Upgrade PC Boards


Gregory Braun

Posts: 5
Join date: 2009-02-18
Location: Brookfield, WI U.S.A.

Dynaco Mark III Upgrade PC Boards

Post by Gregory Braun on Sun Feb 22, 2009 7:26 am

I'd like to upgrade a pair of Dynaco Mark III
power amplifiers. Both units are currently
bone stock.

Tubes 4 HiFi offers an upgrade board for the
Mark III based upon their Stereo 70 upgrade
board, while DIY Tubes offers their Poseidon
upgrade board. Triode Electronics also sells
an upgrade PC board for the Mark III amplifier.

What are the differences, benefits of each?

Thanks in advance.



Posts: 58
Join date: 2009-01-19

Mark III boards

Post by danf on Tue Feb 24, 2009 7:16 am

I've used the Triode boards for an earlier set of Mark III's and liked them. I am now building up a set of the VTA (tubes4hifi) boards. I haven't considered the Poseidon boards because they use a solid state current regulator and this bothers me for some reason.

The Triode boards use a cascode (triode pair) input stage and a long tailed pair phase splitter. The VTA boards use a single 12AT7 input and a similar phase splitter.

The VTA Mark III board layout isn't quite as refined as the ST70 board, but it shares two very nice features with the ST70 board: (1) An on-board bias supply with individual bias adjustments for each tube. This makes for a clean layout. (2) On-board filter caps for the input and phase splitter stages. This means that you can parallel two sections of your filter cap to provide more reserve for the KT88 supply. I am trying out the Dynakitparts 550V 80-40-30-20 filter cap with this board.

A test report will follow when I finish.
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