WOW!!! That's all I can say
after hearing this beast. I now understand what everybody was
talking
about
with the 300B. This is a
very powerful tube, capable of stunning bass reproduction as well as
those
well-known velvety smooth highs
and midrange. I feed the amp directly from a CD player and run
Klipsch Cornwalls. No tone
controls to get in the way. Like my other creations, this
amplifier
uses
Hammond transformers and
metalwork.
I'm very pleased with the quality of the Hammond transformers.
I think they are good performers
at their price level. I have yet to try some of the more
expensive
transformer
brands, Magnequest, Tango,
Tamura,
Bartolucci, etc. in part because I get such good sound from
these.
The
outputs are the 11 pound 1627SE,
the power transformer is the Hammond 378CX which is rated at 400-0-400
at 465mA with a 6.3 volt filament
winding. I used separate Hammond filament transformers for the
rectifier
and the 300B filaments. I
take the B+ from the center tap of the rectifier filament transformer
fed
to a small
Solen cap before the chokes to
tune the B+ supply voltage to 435VDC.
Tube line up is: 5Z3, 300B,
6SN7, 300B, 6SN7. The 5Z3 is a NOS National Union that I got from
Antique Electronic Supply, as are
the RCA 6SN7s. The 300Bs are Russian, made in the Reflector
factory
which makes Sovtek tubes.
I think they are several years old, but unused. I got five of
them
from a
friend at a really good price and
that's what prompted me to tackle this amp. I've shied away from
the
Western Electric tubes due to
their
high cost. The big oil caps in the center of the chassis are from
Angela
Instruments. They appear
to be very high quality, rated 50uF and 30uF at 370VAC or about 520VDC.
I was surprised when I opened the
box from Angela and the caps made a sloshing sound from the oil inside.
Steve advised me that the
sloshing
sound was normal and that the caps are filled with canola oil.
I normally use oval cased motor
run caps which are filled with a gel material, so they don't slosh.
I had a bit of a problem with the
volume control for this amp. I purchased an Alps "Black Box" 100K
log
taper stereo version which proved
to be defective. It caused a lot of noise from both channels and
eventually
the right channel died until the
volume pot passed the halfway mark, at which point it was too loud to
appreciate.
I temporarily replaced the Black
Box with a cheapo Alps pot from Radio Shack until I can get a proper
volume control. The amp
plays
with more than ample volume without audible distortion. I don't
have
proper
instruments or technical
knowledge
to do distortion measurements, but my ears don't lie to me. I have
auditioned the amp on everything
from Ry Cooder to Metallica and it sounds really good.
Also, like my other amplifiers,
the chassis, bottom cover and transformer end bells are powder
coated.
It's so
much easier than trying to get
a good paint finish. A company here in Tyler, TX does it for at a
reasonable cost.
I welcome any questions or
comments
from other tube hobbyists.
Click here
for a schematic, rough as it is. Please let me know if you see
any
obvious errors.
If you'd like to see some
close-up
details, click here.
Comments? rkoonce@dsityler.comt
