Alpha 8100 Product Review

PRODUCT REVIEW
Alpha 8100 HF Linear Amplifi er
Reviewed by Norm Fusaro, W3IZ
Assistant Manager, Membership and
Volunteer Programs Department
The Alpha 8100 is the latest manual-
tune legal-limit RF power amplifier from a
company that has a long history of producing
brawny, high quality products. Using the
latest microprocessor technology to monitor
critical functions and other high quality com-
ponents to provide smooth and easy opera-
tion, the Alpha 8100 is capable of producing
a clean, robust signal with minimal drive on
all amateur bands from 1.8 to 29.7 MHz.
First Impressions
The first thing that I did after bringing the
Alpha 8100 down the basement stairs and
into the shack was to sit down and rest. This
desktop amplifier is no lightweight, tipping
the scales at 69 pounds. While catching my
breath I admired the sharp looking front
panel and large LED bargraph displays for
power and current/voltage/gain. The front
panel is very similar to the Alpha 99 that this
amplifier replaced in the product line. For
such a heavy box, the unit has a relatively
small footprint compared to other desktop
legal limit amps currently on the market.
ARRL Lab Test Engineer Michael Tracy,
KC1SX, had already unpacked the '8100 and
installed the heavy transformer so he could
put the amplifier through its paces. The trans-
former is shipped separately to avoid damage
during shipment, and it's a simple process
to install it. Installation involves removing
the cover, securing the transformer with four
screws and plugging in a couple of multipin
connectors. The well illustrated manual is
very clear on how to do this, and Alpha even
provides a piece of wood cut to the right size
to position the transformer and slide it into
place. The manual also recommends checking
the tubes, chimneys and hardware to make
sure nothing came loose in shipping.
Before plugging in the unit I removed the
cover to check for the proper voltage taps on
the transformer. The Alpha 8100 has a built-
in power supply that is capable of function-
ing with a variety of ac input voltages. Line
voltage selections are easily accomplished
by moving the taps on the terminals located
in the power supply section of the amplifier.
As is typical of legal-limit power amps, the
Mark J. Wilson, K1RO
70 April 2007
user must provide a power cord connector
compatible with the station's wiring.
While it is possible to run the amplifier
at reduced power from a 90 to 130 V line,
the manufacturer strongly recommends that
the amplifier be fed by a dedicated 200 to
240 V ac circuit with 10 gauge wire capable
of a minimum of 20 A. It's well worth the
time and effort to install a proper 240 V line
for your amplifier.
Station Considerations
The manual offers a number of safety
notes. In addition to the many warnings about
electrical safety, there's a section reminding
users about RF safety. If you are upgrading
your station from barefoot power levels, it's
time to review the RF safety information and
do another station evaluation. See www.arrl.
org/tis/info/rfexpose.html for details.
Legal limit amplifiers require that you
use heavy duty station components, and
the manual devotes several pages to station
considerations. In addition to the previously
mentioned power requirements, consider-
ation needs to be given to antennas, feed
lines and connectors, switches, antenna
tuners, relays and grounding. Every com-
ponent must be rated for legal-limit op-
eration. You can read more on this subject
Bottom Line
The Alpha 8100 effortlessly deliv-
ers a clean 1500 W of RF from 160
through 10 meters. Consider it a long
term investment in your operating
pleasure.
Product Review Editor
in the July 2006 issue of QST.
The Alpha 8100 is rated to work into
antenna systems with an SWR up to 2.5:1.
The manual cautions you to tune the ampli-
fier carefully when SWR exceeds 1.5:1. As
noted in the Station Engineering Consider-
ations section, high SWR can cause exces-
sive voltages and currents at various points
in your feed line system. You need to watch
for signs of arcing or other damage when
running high power into a high SWR.
A Look Under the Hood
While under the cover of the '8100 I took
notice of the clean layout of components and
the quality construction that Alpha has long
been known for (Figure 1). Interior partitions
ensure good RF shielding and add to the
structural rigidity. The Alpha 8100 is built
around a matched pair of rugged 4CX800
(GU74b) tetrodes from Svetlana. These
ceramic tubes are operated in Class AB
and reliably provide 1500 W output with
approximately 50 to 60 W of drive power.
Although there are several "workhorse"
amplifiers in the amateur market that use
4CX800 ceramic tetrodes, the Alpha 8100
distinguishes itself in several ways. The
sturdy cabinet construction, vacuum relays
for fast full break-in (QSK), heavy duty
switches and components and an extremely
quiet blower used to cool the unit are just a
few worth mentioning.
The '8100 makes use of microprocessors
to monitor all critical currents and voltages in
the amplifier, as well as to control relays and
1
D. Hedin, "Learning to Live with a Linear," QST,
Jul 2006, pp 37-40.
k1ro@arrl.org
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