Alpha 99 Linear
Alpha's latest made-in-USA HF amplifier utilizes the workhorse Russian 4CX800A
Bob Hutchinson, N5CNN
Alpha King of the hill in legal limit + Ham radio linear amplifiers? Well,
there's a lot of information in this article - so you be the judge.
Click any picture larger>
Inc. of Boulder CO is the new manufacturer of Alpha linear amplifiers. In
keeping our promise to review amplifiers we ordered this model 99 from
Crosslink, Inc. on September 7, 2001, planning for a November article. At
the time of our order it appears that none of the new model 99s had yet
been shipped. This one was received just before Thanksgiving.
the new Alpha 99 and dealing with Scott Ehrhorn and John Tuttle was a good
experience. Everything was well documented and email acknowledgements were
as expected - good business practices throughout the process. Delivery was
a few days over two months. I understand that delivery is improved
since production of this unit.
To my knowledge, this is the
first Alpha made in the USA to be equipped with the Russian Svetlana 4CX800A/GU74b
ceramic-metal tetrode tubes.
OK, lets get this
straight again. As you may have read in the review of the
amplifier, I love the big warm, glowing glass tubes. After publishing the QRO
review I came into possession of a nice Ten Tec Titan legal power +
amplifier that utilizes the 3CX800 type Eimac tubes. Well, there is some to
be said about indirectly heated cathode tubes - dramatically reduced heat
and lotsa power in a small package.
After removing the model 99
from the big box my memory worked as it should, it reminded
me that Alpha has been doing this for a while. First impression is the
small size of the amplifier. Upon removing the cover and briefly examining
the innards, my memory again reminded me that Alpha has been doing this
for a while. The lay out is standard for most single box amplifiers made
today. It's a U shaped pan with front to back divider/stiffener to
separate left RF section from right side rectifier, power supply and
circuit board section. The cover becomes an integral structural member
when completely attached.
In it's class, legal
limit +, it is a small, compact amplifier. It stands eight inches above
the table with the front support bail folded. Other: 17 inches wide and 16
1/2 inches deep plus hardware
attached to the rear panel, such as the extra
fan. I have not weighed it but it is the lightest in it's class, shipping
weight is 80 lbs. for both cartons. Even though the
amplifier is small, the components inside don't seem to be crammed in.
Everything is orderly and there is plenty of evidence that service will be
easy, if ever
needed. Circuit boards and components utilize quick disconnects and plugs
so removal or replacement will require minimum solder melting, if any.
Examine the pictures to
see the quality components, design and construction. I have been into
quite a few amplifiers in my days and know the good stuff when I see it.
During the photography session in our light tent I get to see everything
and photograph it. The first, and most apparent, item is the front to rear
divider wall. It's an extensively ventilated quality fabricated aluminum
divider. Concave clearance for the tune and load capacitors are stamped
into it. The fast vacuum T/R relay is mounted in a large
rubber grommet and has shrink tubing on the soldered leads to effectively
dampen noise that normally would be transmitted to the case. The squirrel cage
type blower motor and cage is mounted
on a dense, sound insulating foam rubber pad to reduce noise while the
black housing is firmly mounted to the box
The AC primary, nine conductor connector for the transformer is firmly
mounted to the back panel as a receptacle. Great attention has been paid
to wire and cable containment, routing and security. All is first rate
throughout the amplifier. Although I have not been inside the patriarch of
the Alpha family, the 87A, I suspect the 99 and 87A share some components.
The Rusky tubes
The tubes appear to be
larger in diameter than the 3CX800 type tubes. The 4CX800A/GU74b tubes are
operated in a grounded-cathode, grid driven tetrode configuration. Because
of the low drive voltages required, input from the exciter can be loaded
with a non-inductive 50 ohm resistor while a fairly simple
circuit compensates for tube and circuit reactances in the higher
frequency bands. This provides a very low input SWR situation across the
Amateur HF bands. No tuned input circuits are required. This is a cost
saving plus for manufacturer and purchaser.
Tune & Load different
The tune and load capacitor
do not have the normal mechanical vernier drives.
Instead, the two-section capacitors are switched for the bands to provide
an "electrical vernier" function.
Auxiliary muffin fan added
Alpha claims that this amplifier provides 1,500 watts peak power output on SSB,
keyed CW, SSTV, RTTY, digital modes or FM, with no time limit. They also
mention that "continuous
key-down" , as in brick-on-the-key operation, for more than five minutes
requires additional cooling. Well, I knew that. You knew that. We
all knew that, didn't we? This unit was shipped with the optional
auxiliary muffin fan attached over the rear air inlet. The fan is also
required when the model 99 is powered by 50 Hz AC mains.
suspect the centrifugal blower is completely adequate for the tubes, but,
in high power output situations better circulation is required to the
front of the
transformer where the rectifier/filter and control circuit boards are
located. Especially, if transformer efficiency is reduced when using 50 Hz
AC power. For me and most of those trying to wear out microphones, the
normal model 99 cooling system is more than adequate.
Vacuum relay QSK
Full break-in QSK circuit
provides wonderful enhancements for telephone-like
SSB conversations or efficient high speed control for all other modes.
As good as the best I've seen. Nicely bound, complete with schematics.
the power supplies?
The circuit board area includes the HV bridge rectifier, filter capacitors, meter and
control circuits and components. Alpha has stuck with the full wave bridge
rectifier. The filter section is populated with nine 220mf electrolytic capacitors,
each rated at 400 v., providing about 25 mf filtering and a working PIV
protection of 3,600 v.
A special Peter Dahl
Hypersil transformer of the 3.5 kw + capacity provides plate and other AC
voltages. The design no load B+ voltage should be 2,900 VDC. Our
instruments measured 2,969 VDC with 234 VAC from the mains. Other secondary power from the transformer provide
voltages for the requirements of metering, grid, control, bias, soft start and
QSK T/R circuits.
Some assembly required
Not much though - the
Peter Dahl transformer has a nice strap for lifting. It also has the
1/4"-20 nuts attached to the top side of the transformer mounting plate so
the furnished stainless cap screws with washers can be quickly run in from
the bottom of the case, thank you. The pan has several guides to locate the
transformer and all three electrical plugs are pre-fitted, pre-shaped and in place for
quick installation. It's a snap. The cover fits great. I put it back
together sans one screw and no extras came with the unit.
For HF RF
power out our test bench is equipped with:
Coaxial Dynamics 83000A peak reading directional RF wattmeter.
Bird 43 directional RF wattmeter.
Coaxial Dynamics 81000A Directional RF Wattmeter.
These with same slug values, usually 2500 watt, connected in series with a 3500
watt low pass filter, a 7,500 watt. antenna switch utilizing Jennings vacuum
relays for access to 3000 watt fan cooled dummy load located outside of
building, or 75M & 40M dipoles, and verticals for higher HF frequencies.
Testing of wattmeters is performed by placing in series with the wattmeters
mentioned above for comparison.
But does it run?
Well, let's see. Yes,
it lights up, lotsa lights, red, green, green LED bars, flashy stuff. A red LED stays on
until the internal gyros wind up to speed. Kidding, no gyros, just indirectly
heated cathodes being heated up. Tuning is easy and straightforward. If
you've developed good tuning habits or can read the manual, it's a snap.
The green LED instrument bars do a fine job of feedback to the operator.
The continuous green LED bar displays of forward and reflected power are
especially impressive. Reflected power green bar display runs to red when
it exceeds 10% of forward power. The forward power green bar
display runs to red when power out exceeds 1500 watts.
red "Bad Boy" sign pops up and the audio alarm message, "Bad Boy", "Bad
Boy", "Bad Boy" sounds until power is reduced to legal. Of course if you're on
a phone band with VOX, other Hams will
hear this and know you for what you really are.)
I went through my
systematic load test for the following bands on the dummy load. Results below
coincide with the tune up table furnished with the amplifier. Drive signal is CW.
Over drive it
The above test table reflects the loafing facts. For you bad-boy
wantabees, this amplifier is just loafing at 1,500 watts CW output. On
each band during the tests, except for 10 meters, I continued tuning on the dummy load in short
segments and increasing drive until full output of the 110 watt exciter
was reached or power out exceeded the full scale capacity of both
wattmeters (2,500 watts). In all cases we were beyond the accurate measuring
capacity of both meters. This means we could not accurately determine the maximum
power output but it's 1,000 plus watts beyond legal limit in CW mode.
Superb legal limit + HF linear
amplifier. For a competitively priced, single box legal + amplifier, the
model 99 is smaller, lighter, more compact and more powerful than any
Amateur Radio amplifier this writer has handled, used or examined. Wonderful design,
excellent components and quality workmanship throughout. But - - - is
Alpha still King-of-the-hill? Well, hell yes. I knew that. You knew that. We all knew
that. See all the Alpha amplifiers at their new
At the beginning of
this article I mentioned that I love the warm, glowing tubes. I still do,
but may use one of these powerhouse ceramic-metal jobs in warmer weather - less heat, ya-know?
Bob Hutchinson, N5CNN
President and Founder
Wireless Industry Association
If you would like to
publish an article here contact Bob