4
INTRODUCING THE L-5000 DHT PREAMPLIFIER
Allnic Audio and the Direct Heated Triode Breakthrough
In the early years of the last century, the directly heated
triode was invented independently, and almost
simultaneously, in the USA and Austria. This simple device,
an anode, cathode and a grid in a vacuum contained in a
glass bottle, transformed the world. With all the
applications in which it has been employed, and with all the
changes in electronic design for audio reproduction that
have occurred since its invention, it is remarkable that over
one hundred years later, the very first triode, the simplest
vacuum tube audio signal amplifier, despite the
imperfections ascribed to it, remains a favourite audio
amplification device of many devoted music lovers
worldwide.
Debate, on both subjective and empirical bases, about the
quality of the directly heated triode’s sound reproduction
potential continues even today. One of the interesting
aspects of these debates is the degree to which they ignore
analysis of common, fundamental assumptions based on
decades of circuit and mechanical design experimentation
and compromise, about the use of these devices. Indeed,
because of the difficulties in application of directly heated
triodes in audio circuits, many issues arising out of circuit
design problems related to them have evolved into
assumptions about the audio characteristics of the valves
themselves.
Allnic’s Mr. Kang Su Park has spent a lifetime studying and
designing circuits and transformers for application of direct
heated triodes for audio reproduction. By questioning basic
assumptions about the valves and re-examining the original
and many historical variations of circuit designs for them,
and experimenting constantly in a framework of rigorous
application of theory, Mr. Park’s work has resulted in some
remarkable audio power amplification devices. With the
300B, for example, his creations produce significantly more
power than is expected (without shortening valve life
because the power increase is not achieved by increased
bias), in conjunction with exceptionally low distortion and
wide bandwidth.
Now, Mr. Park has successfully combined elements of what
he has learned and invented over decades to the
development and production of a pure, direct heated
triode (DHT) based preamplifier. The main breakthrough,
which came after several years of work applying all he
knows, was the design of a circuit, valve and transformer
combination the measured results of which astounded
him. The purity of its square wave reproduction – as
perfect as anything he had ever seen from a DHT valve
amplification circuit – had him questioning what he was
seeing! Of course, he tested and re-tested, replicated and
recorded these results many times before assuring
himself that there was no mistake.
With such an unprecedented outcome for the circuit
design, Mr. Park could not be satisfied merely with
placing a DHT stage after one or two prior stages of
amplification using indirectly heated triodes. This
approach is used in a number of commercially available
preamplifiers using DHT’s, but it is a compromise. It does
not result in PURE DHT amplification; it necessarily
introduces the characteristics of indirectly heated triode
sound into the circuit, so the output DHT’s are only
amplifying a signal already affected by the indirectly
heated triodes in the prior stage or stages.
Mr. Park, though, has created a preamplifier that uses
DHT’s at each amplification stage. In his design, the
output stage DHT’s are not merely amplifying the signal
from previous, indirectly heated triode stages. The L-5000
DHT preamplifier is pure DHT - from input to output.
Of course, Mr. Park is not the only builder who has
accomplished this, but to our knowledge no other pure
DHT preamplifiers have been commercially available.
There are serious and significant reasons why such
preamplifiers could not be acceptable in the marketplace.
First among them has been the enormous problem of
microphonics. One of the many special elements of Mr.
Park’s design is
reduction of microphonic influence on the
DHT’s
.
Where others have sometimes accepted the effects of
this problem because even with it they prefer the incredible
realism of the pure DHT approach,
Mr.Park has succeeded in
creating a circuit and mechanical design that
reduces the
DHTs’ susceptibility to microphonic influence to insignificance
.
Like the Allnic L-3000, which is an indirectly heated triode
preamplifier, the L-5000 has a noise floor that is
effectively absent.
The Allnic L-5000 DHT preamplifier is THE WORLD’S FIRST
COMMERCIALLY PRODUCED, PURE DHT PREAMPLIFIER.
Currently, the L-5000 DHT’s large output tubes are very
rare items, produced many decades ago. Allnic has been
able to secure a limited number of these valves, enough
to produce an also limited number of the L-5000 DHT
preamplifier. ONLY A LIMITED NUMBER OF UNITS OF THIS
DESIGN WILL BE MADE. This allows for valve stock to be
