[Phil Allison[_3_]]

"Patrick Turner"

I have very nearly finished re-engineering a pair of Dynaco MkIV monos.

** Question for Pat.


The Dynaco Mk IV uses two EL34s in UL mode with a 470V supply - OK.

The published data for that UL of operation includes THD curves that barely
exceed 1% below clipping - with NO feedback applied .

However, Dynaco claim virtually the same THD figures, with circa 20dB of
feedback applied ??

Is the 7199's pentode gain stage mainly responsible for this anomaly ??

For comparison, the Quad II use two, low cost, EF86 pentodes in
differential mode to provide gain and phase inversion. The output stage uses
local (cathode) feedback, plus overall feedback but is otherwise
conventional PP with KT66s or 6L6GCs performing equally.

The Quad II achieves 0.1% THD at rated power and 0.05% THD at circa 10 watts
or less.



..... Phil