Aphex
Thermionics
- Division of Aphex Systems Ltd.
Thermionics
refers to the
practical use of the “therm-
ionic emission of electrons”.
Vacuum tubes use thermionic
emission by heating the metal
cathode to incandescence.
Electrons are consequently
emitted into space from the
high temperature cathode surface. The
emitted electrons become the source
of current flow through the amplifying
tube. A thermionic amplifier, then, is just
another name for a vacuum tube ampli-
fier.
Aphex
Thermionics
:
The Story
That patent was issued to inventor
Donn Werrbach and assigned to
Aphex Systems Ltd. on September
12, 1995. A close examination
of the patent reveals that it is a
“method” patent and not just a
patent on some particular circuit.
That means it is possible to apply the patent
teachings to a wide variety of applications and
circuit variations with full patent protection.
Other manufacturers will not be able to duplicate
our RPA based products. Nevertheless, no one at
first really knew just how significant that inven-
tion would prove to be.
The first product to apply an RPA circuit was
our model 107 Thermionic Mic Preamplifier.
The outstanding sonic quality of the unit has
become world reknown and tens of thousands of
units have been sold. Anything new and better is
sure to stir up controversy. Not surprisingly, the
success of our tube circuitry has alarmed other
manufacturers of tube products. Some of them
reacted with claims that our circuit is not “clas-
sic” and therefore not “real tube”. The claim
is ludicrous, but less than erudite
reviewers hooked on conventional-
ity have misreported it. For example,
one particularly delusional reviewer
rather condescendingly declared it
nothing more than a “starved plate
amplifier” (as if he ever saw one).
Fortunately, these cases are greatly offset by the
phenomenal word of mouth praise and promo-
tion we have received for the RPA products from
their actual owners over the years.
Since the original patent was filed, we have dis-
covered new ways to create many useful circuits
with RPA principles that would be impossible
to realize with conventional tube circuitry. For
example, the Model 1100 MkII Mic Preamp incor-
porates a very low noise second stage opamp
using just one single triode RPA. Future products
will feature many new tube circuits now in the
laboratory. Aphex’s unique servo balanced input
and output stages translated into RPA implemen-
tations are examples.
It has become apparent that the principles of the
Page A-3
RPA patent are the keys to gaining the unparal-
leled sonic benefits of tubes in an almost unlim-
ited range of audio products. To fully distinguish
our highest level of tube based audio products,
we created the division of “Aphex Thermionics”.
Watch for more exciting new products from
Aphex
Thermionics
.
Abstract From U.S. Patent Number 5,450,034
“A reflected plate amplifier (RPA) for use with electronic audio equipment. The RPA comprises an input circuit for receiving an input signal, a vacuum tube,
a plate current reflector, and an output circuit for delivering an output signal. The vacuum tube has a control grid coupled to the input circuit for receiving
the input signal, and a plate for delivering a plate current responsive to the input signal. The plate current reflector is a transistor having an input terminal
coupled to the plate of the vacuum tube for receiving the plate current, and an output terminal for delivering a reflected current which is responsive to the
plate current of the vacuum tube
and therefore responsive to the input signal, while the plate current reflector holds the
plate voltage of the vacuum tube
substantially constant for a wide range of the plate current of the vacuum tube.”
Dual Triode
