I've read this thread with great interest. I roamed
around the SET OTL world before I finally chose the
Berning Siegfried 811-10 amp, which is the 12ish W/Ch
version using Svetlana 811-10 output tubes. He also
makes a 300B output version, but from all I'd heard and
read the circuit is really optimized for the 811-10 and
sounds great. Also, 811-10 tubes (and 572-10) are
plentiful and cheap.
I wrote to the editors of Listener magazine a while back
and asked them to do a shootout of the various OTL
amp designs . . . certainly there are differences between
circlotrons vs. ZHOTL vs. other strategies. I also think
that the ZH270's performance in these listening tests
is wonderful, considering what I perceive to be its place
in the world of amps.
In my mind, opinion only, the ZH270 represents a tubed
"workhorse" amp which is a great-sounding bridge for
folks who are used to very-high-quality solid-state
equipment and want to move into tubes. Of Berning's
commercial line (prototypes aside), it is definitely
the beefy brother intended to drive lower-impedance
lower-sensitivity (read: SS-type) speakers well. So
you can get into great-sounding tubes with your
existing Linns or whatever it is that strikes your
fancy.
Of course, there's a lot of taste-issues (chacun son
gout) in tube amps. There are hard-core tube-ophiles
(like me) who greatly prefer low-powered SETs with
high-efficiency speakers, and I can tell you that as
far as that goes, the Siegfried is one of the best
options on the market, and is also is a "good deal"
($5K-$6K) relative to other high-quality SET/OTL amps.
Speakers are arguably the weakest link in my system;
I've got an "inexpensive" pair of Moth Audio Cicada
horns that the Siegfried drives with aplomb. And with
bass, more than you'd expect from their low-end rating
of 60Hz.
Anyway, I guess I just wanted to say that I think the
discussion is quite interesting, but there are (as folks
have mentioned) a LOT of different ways to use tubes.
Push-pull OTL (like the ZH270) is a relatively uncommon
beast; OTL is more common in the low-powered single-ended
triode realm. So who knows.
Also, regarding NOS tubes. I think you can make a huge
difference with the tubes. Not so much with the outputs
as you can with the inputs, as someone has mentioned
using NOS 12AT7s. The Siegfried has 6 triodes/channel
in the form of 2 6SN7s, 1 6J5G, and the output 811-10.
I've got 1940s VT-231s as the 6SN7s and 1950s Tungsram
6J5Gs, and I think the sound is a world better than it
was with the stock Russian stuff. That said, I think
Svetlana and Sovtek are putting a lot into R&D in their
new tube designs (like 811-10, 6H30Pi, etc.) but don't
do as well with their remakes of old designs like 12AT7.
Sorry to ramble. Great discussion!
Stuart
