O W N E R S M A N U A L
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TUBES - input
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The smaller 9 pin input tubes in this amplifier are dual triodes configured as an SRPP
stage to give maximum voltage swing with the least number of parts. The only
alternative is to use two gain stages with an additional coupling capacitor. Since the
amplifier design only has one coupling capacitor, we certainly would hate to DOUBLE
the quantity in this otherwise extremely transparent amplifier. The tube used is our
favorite Russian NOS military grade 6N1P-EV. (In Russian that reads 6h1n-EB, which is
what is printed on the tube) Alternately you can use 6922’s which are a touch less
warm but slightly more dynamic. Using 6DJ8’s may or may not work depending on the
brand and condition of the tube. This is because the voltages used are on the max
end of what a 6DJ8 likes to see. Alternately, you can also use the Russian 6N2P-EV
for more gain, a more open and lively sound. There are two grades of this tube (as
there is for the 6N1P) and the easy way to tell the military grade from the consumer
grade is the pins. The better tubes have shiny plated pins, while the consumer grade
are un-plated and dull looking.
With the 6N2P the difference in sound between the two grades is pretty obvious. The
better grade has more definition and is tighter. These tubes are also quiet. The
consumer grade is more musical sounding, but typically noisier. The consumer grade
usually requires you to have two or three pairs on hand to find one pair that is quiet
enough to use and enjoy - but they are inexpensive.
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TUBES - rectifier
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The rectifier tube in this amplifier is located directly in front of the power transformer.
DO NOT TOUCH IT WHEN IT IS ON as it will be HOT and could burn your hand. The
amplifier typically ships with a 5U4G rectifier tube. There are many different brands of
5U4 type rectifiers both in New Old Stock (NOS) and in current production. Each will
have a subtle effect on the sound of your amplifier.
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There are also some compatible substitutes that you can try which include 5Y3GT and
5AR4. The 5AR4 is an indirectly heated rectifier with a soft start up so it may be a bit
more expensive than the 5Y3GT and 5U4. A popular rectifier tube that many people try
to substitute is the 274B. There are different manufactures and different types of 274B
rectifier tubes. Of the ones we’ve examined, they all required no more than a 10uf
capacitor in the first section of the power supply. Very few tubes amps today use that
small of a value. The SE34I.4 uses a 47uf capacitor in this location which can cause a
vintage 274B to arc on start-up and thus reduce it’s life. We have found a tube labeled
274B by Valveart that we do not find to be a real copy of a 274B but rather a beefed up
5U4, which happens to work well and look great so it is often shipped as the stock tube
in this amplifier.
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Decware High Fidelity Engineering Co., East Peoria IL, USA www.decware.com
