S-240 Monoblocks All Triode Push-Pull DIY Fun;
or How I ruined my summer...
SETH 2A3 S-240 Monoblock
Step by Step Manual
while some say miracles don't exist, others don't need to see divine
intervention; some just need to see something so improbable, that
even divine intervention seems more likely. But alas, miracles DO
exist as evidenced by Pantheon Audio's Dr. Jean-Francois Lessard's
TEARING APART of one Seth Monoblock to rebuild and take shots of
the process! And amazingly enough, we now have a nice simple PDF
package, albeit a huge one (over 6.45MB), with pics and step by
Yes, can I get an AMEN BROTHER!?
Yeah, well a simple, "that looks great Jeff" will suffice
Can I have another A-MEN, BROTHER!??? Praise thy Pilsner and Sweet
Quebecian Solder fumes!
To Download, right click Seth 2A3 Manual pic; select SAVE TARGET.
have the latest FREE Adobe Reader? Go here.
Note, this document is also available in MS Word.
Belle Gueule, The Official Seth Build Beer -
Responsible for Jean-Francois AGREEING TO this in the first place!
Jean-Francois Lessard finally gets his AC working.
OK, so this is pretty late but according to Dr. Jeff, the results are
worth it, or so he says. He is planning to send it down to the NC coast
for an audition so we don't have to only take his word for it. Based on
my listening time with his other projects, I would say it's a no-brainer.
Jean-Francois describes the project below:
For now, some
insight on the design to come. Phase splitting is achieved by an MQ
EXO-173 PPS. The OPT is a MQ "Peerless" S-240-A.
The driver is simply resistor loaded. I tried some elaborate pentode/MOSFET
constant current source applications as well as a choke load approach.
In the end, a simple resistor proved to sound really good and end up
cheaper and much easier to do (yet Jeff ended up going further with
the excellent BCP-16NiGC grid choke)
The driver is the venerable 6C45-Pi. Not usually my first choice but
an appropriate one considering the comments long ago from a certain
Gary Dahl, this in relation to driving a pair of 2A3 through a EXO-173;
seems the PP configuration will require a driver with cojones, for lack
of a better word. Since you can get 40 mA from the 6C45-Pi with no sweat,
it turned out to be the final choice. With this configuration, the amp
is quiet as a tomb and sounds VERY nice.
Of course, there's the politically correct tube rectification which
ain't too bad for sonics either. I'm running it now with 5U4G but GZ34
are OK too. Ditto with a 5R4
I'm warning you
guys, don't expect something really elaborate as a circuit with this
amp. This amp was designed with the write up of a"how to build
a..." article in mind. This kind of article usually destine itself
to rookies in the DIY Audio world so I had to keep in mind simplicity
of design and building plus a relatively low building cost. All this
while achieving excellent sonic results. In this actual case simple
just became simpler than I initially thought.
So what is left between now and the time the article is online... Simply
dismantling one of the amps and rebuilding it while taking pictures
of the whole process.
Well, when I read this last sentence, I had
to suppress an audible groan. So all that's left is simply dismantling
one of the amps and rebuilding it while taking pictures? In Quebec-Lessard
time this might just equal the new Happy Holidays Christmas/Hanukah
2A3 Project! I'll make sure this doesn't happen...I want to hear the
beasts before the leaves fall. Take a look at the menu at left for the
iron deals as well as a few surprises.
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