Jan's
Tube Audio Page
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I have always loved
tubes. My first amplifiers were a couple of home brewed things built after
the schematics in Electronics November 1953 issue and was called Linear
standard. They used a 12AX7A, a couple of 6AU6 as drivers and a pair of KT66.
I got them from a friend of my father back in the late 60's. They were
scrapped after a while, I was too young to realise the value of them. I still
have a couple of the KT's and one of the output transformers from them. The
KT's are the real stuff and still strong. Around 1989 I returned to
tubes and designed my own tube amplifier. It's still under development but
sounds like the better amplifiers in the good old days. Tube selection was
easy since I used what I had available at the time, both NOS and used. Used
tubes are useful when designing, replacing them with NOS when it's working.
For some reason I like low gain triodes like 6J5, 6SN7 and 12AU7/ECC82. The
preamplifier is totally feedbackless and the power amplifier has a very low
feedback. It's a compromise between dynamic sound and distortion. Nothing is new under the
Sun, all feasible tube circuits has already been invented. My amplifier is
not an exception, the configuration has its roots back in the 50's. Single
tube input, long tailed pair phase splitter and a ultralinear output with
cathode bias. This power amplifier is
now scrapped and the materials have been recycled into my newest project, the
HFTA. You can find this under Projects HFTA2 to the left. The preamplifier is
powered by a tube regulated power supply using EZ90, EL90, EC92 and 85A2. I
will add a schematics of this later. Schematics
Power output is around
22W into 8 ohms. Low feedback gives a dynamic sound but also some harmonic
distortion but the low impedance plate load keeps the annoying odd harmonics
down, I have also built a small
amplifier using 3 6DJ8 and 4 6BQ5. The output irons are small, too small, but
with very interesting properties. I bought these back in '89, they are
unmarked but reliable sources told me that they are wound by Partridge. The
sound is very promising but the cores saturate at the extreme lows. The tubes
are cathode biased into pure class A. I'm looking for a quad of matched
6BQ5's, the current set is not very well balanced, probably causing the
saturation. |
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Update Jun 2005: The old power amplifier
has been replaced with HFTA2. Update Jan 2004: I added improved versions
of the RIAA amplifier. Update Dec 2003: This page is my oldest
alive, unmodified since 1996 until now. I have saved a copy of
the original for nostalgic reasons, find
it here Still using my Quad
II’s. I have redrawn the schematics above to make them more readable.
The EL34 does not like being fed from a single 350V source so it will get a
separate 400V supply for the prestages. The links below are old
and may not work. |
Tube audio links
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Last modified 2004-01-31