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Alpha 87A
Top of the line Alpha. Knobless Ham Radio legend?
by Bob Hutchinson, N5CNN

Has Alpha combined a special microprocessor with their amplifier expertise, sans the knobs, and produced a legend? If the Alpha 99 is King of the hill, what could this Alpha be?

Most reading this know or talk to some of the guys on the air that use the the 87A. You may have thought, "Why would someone pay that much money for an amplifier?" or "Does he have too much money to spend?" or "Is the investment rationalized by having the best answer to the popular on the air question - What amplifier are you running?"

Let's do a really close-up examination and see if this Alpha 87A will boot up and confirm it's own legend and justify it's $6350.00 price tag.

I took it out of the box and arranged it on the bench so I could remove the cover. Wow! Lotsa stuff inside and no knobs on the outside. No knobs? I don't know, how - - , lotsa buttons and lights and leds and stuff. This is an experience. I'm a knob twister and think of myself as an advanced appliance operator, but I don't know, this is kinda perplexing.

                                                                           Click any picture larger.>>

OK, into the light tent
I'll have this beast on the roll around plant stand for a while with the Olympus digital camera between us. Maybe the fun picture taking will dilute the helpless feeling I have because this amplifier has no knobs. As with the Alpha 99, examining and photographing the innards reminds me again - Alpha has been doing this for a while. Everything seems to be so well planned. Well, it has to be. This Alpha has a lot more components than the 99 and the box is about the same size. That means a lot more design attention is paid to layout to get it all in the box. No wasted space, really well done.

Skunk works
The front end area inside this amplifier is where the micro processor controls, stepper motors and related circuits are located. Maybe later during this review I will open this section for examination, then again, maybe not.

RF section
Alpha quality throughout. Proper switch work. Band switch, Tune and Load variable capacitors operated by stepper motors. All components are the best commercial quality available. No shortcuts.

Centrifugal squirrel cage type blower
Kinda buried under the RF components and mounted on a spongy rubber pad for sound isolation. For shipment two screws are inserted in the back panel to stabilize it. See back panel pictures.

The axial/radial heat exchangers type tubes require air under pressure so it can go around corners, through a plenum chamber and through the tube fins in enough volume to satisfy requirements of normal high power use. Alpha recommends the ancillary muffin fan on the air inlet for really high power, high duty cycle operation.

The auxiliary muffin fan is not needed for low duty cycle operation. A switch is provided on the back to turn it on if needed for high duty cycle, high power operation.

Somehow, probably through selective breeding, the squirrel in this squirrel cage blower makes less noise while performing rotation duties than most squirrel cage blowers used in amplifiers. However, this amplifier produces some other noises that are very unusual. It groans. Un-huh, sure does. I kinda like hearing the groans. More below on all the unusual noises.

Good choking
Actually two plate chokes with a plate choke relay operated by the processor.

The Eimac tubes
A pair of shiny 3CX800A7 Eimac triodes handle tube duties. While Alpha has switched to the Russian Svetlana 4CX800A/GU74b ceramic-metal tetrode tubes for the Alpha 99, they still use the fine Eimac triodes in this champion amplifier.

Pin diode QSK
Full break-in QSK circuit provides wonderful enhancements for telephone-like SSB conversations or efficient high speed control for all other modes. Silent and fast.

The manual
Pages must be missing, too thin. Any amplifier with a computer running most things and no knobs has got to have lotsa pages of instructions. Nope, all seems to be in order. It has fold out block diagram and fold out simplified schematic.

And the power supplies?
I'm amazed at how little space is used with the high voltage bridge rectifier/filter arrangement. Some caps mounted horizontally some vertically. Two 410K ohm bleeder resistors stacked vertically in parallel, two stacks for each capacitor providing about 100K total for each HV capacitor. An encapsulated bridge rectifier puck, probably rated 3 amps and 3,600 PIV. Similar to the bridge in the Alpha 99. This item cost a lot more than the three or four dollars worth of diodes used in many amplifiers, but it sure reduces complexity and space requirements. If my guess is right, this bridge also produces a lot less heat at high power output.

Upon removing the Peter Dahl transformer from the box I noticed it is a different type than used in other amplifiers. Transformers in all other amplifiers I have examined are shell types having one winding segment and two steel cores banded together with steel strapping. This one has two winding segments and one steel core. The core type has been used in Alpha amplifiers for a while. This one is smaller and appears to be lighter that the standard type but is still in the 3.5KW to 4KW capacity class.

El Paso King
A call to the El Paso King of Ham Radio transformers, Peter Dahl, was helpful in defining the transformer. It is a core type transformer that has benefits in center tapped applications because each winding can have equal resistance. In linear amplifier applications the benefit is smaller size, lighter weight and shape. Core types can be more rectangular in shape, instead of the cube shape of the traditional shell type we are accustomed to. This shape benefit can be handy in an amplifier like he 87A were space is at a premium.
Within limits, the transformer can be designed to fit the available space. Of course, this premium core type transformer has a premium cost. By using more than one winding with secondaries in series, the total length of wire in the secondary is less, resulting in less weight.

Raw, hum laced DC from the bridge rectifier puck is filtered and smoothed by seven tall electrolytic capacitors, probably of around 220uf and 450 volt values each. The measured, no load B+ is 2,757 VDC.

Ancillary power for tube cathode heater, metering, bias, QSK circuits, etc., is provided by multi voltage transformer secondary taps. Examination reveals additional power supply components utilizing the three blue horizontally mounted electrolytic capacitors. It appears this supply is for the microprocessor control system and stepper motors.

Will this top-of-the line Alpha perform? Does it run?
At this point I have been over the operation and tuning section in the manual a few times and feel better about this knobless legend. So let's see if the legend is.

Our test bench is equipped with a  2000+ watt fan cooled dummy load, 3,500 watt low pass filter, Bird 43 and Coaxial Dynamics watt meters cabled in series, each with 2,500 watt slug. The bench has a superb 7,500 w. antenna switch utilizing Jennings vacuum relays, designed and built by this writer for access to 75M & 40M dipoles, 20M, 17M and 15M verticals and the dummy load. Various putt-putt wattmeters are used between exciter and amplifier to measure drive power and SWR.

Accuracy of measurement
We use the average of the two wattmeters mentioned above. Both manufacturer's spec. an available inaccuracy of + or - 5% of slug rating at a mid-scale reading. This works out to be an error factor of + or - 125 watts at mid-scale. The maker's don't even mention accuracy at close to full meter right deflection. Remember, these wattmeters are the bottom of their line, most inexpensive of the manufacturer's offerings.

The groan
After power plug, transformer, cabling, antenna or load installation the manual has just a couple of pages about operating. It just says wait for the three minute wait light to go out and apply 15 or 20 watts of drive. I pushed the ON button, Oh, what's that noise? It was a groaning noise and the bench vibrated. The processor goes through a boot up, I guess. I can only describe the low frequency noise as groan and it lasted about two seconds. The strange noise is not objectionable and it kinda low-freqs the bench. I pushed the OFF button and the ON button again an paid attention to this boot-up routine, yep, two seconds of groan noise.

I slid the amplifier from under the shelf toward the front of the bench so I could better see the action of the band switch, Tune and Load capacitors during the boot up. According to the manual the stepper motors each have 100 steps of range. It appears the boot up procedure runs the three stepper motors to a default limit and then through a complete test cycle and then to the last used band and segment setting. This boot up process takes a little over two seconds.

After boot up and egg timer
Upon applying  20 watts of drive the processor samples the RF bypassed direct to the load and quickly commands the band switch, Tune capacitor and Load capacitor stepper motors and switching equipment to make the necessary adjustment for resonance and amplification of the sampled drive RF signal. Wow! I love Ham Radio.

The manual then says to increase drive for desired output. Follow same procedure for any band or frequency. It appears that Alpha has segmented each band into manageable khz groups with a center frequency or center of segment frequency stored in memory. When RF is applied to the amplifier input and sampled by the microprocessor, the resulting commands take the amplifier off-line, sets the band switch, Tune and Load controls with the fast stepper motors to the proper center frequency or band segment and then puts the amplifier back on-line for Alpha RF power production. This takes about one half second and I am beginning to appreciate the groan and low frequency vibes..

Different testing
Gee, this is neat stuff. My reviews usually have test tables of drive, grid current and power output, but this amplifier is in a different category, a different league. Alpha claims this amplifier will properly adjust itself and produce 1,500 watts into a resonant load or antenna of 1.5:1 SWR or less, any band. The manual does not specifically mention the required drive so I settled on 60 watts for my test. This is two bright bars on the led bar graph, see picture. >

Antenna switch is set on a 2000 watt dummy load with an additional 50 CFM muffin fan augmenting the standard dummy load fan. I started at the 160 meter band with CW drive signal by pressing the PTT. Stepper motor groan and power per the below. I then selected the next frequencies on the exciter and pressed the PTT on each band. In all cases it performed as promised, complete with the wonderful stepper motor groans. None of the maximums for grid or plate current were exceeded. No surprises. >

Then I increased drive to 100 watts for the overdrive test, results below. In a couple of cases the grid and plate currents were at maximum, but no overdrive trips.

Band Loafing Column
60W. Drive
Bad Boy Column
100W. Drive
1.95 Mhz 1,500W 2,050+W
3.925  Mhz 1,500+W 2,250+W
7.235 Mhz 1,500+W 2,250+W
14.250 Mhz 1,500+W 2,250+W
18.140 Mhz 1,400W 2,100W
 21.350Mhz 1,500+W 2,200W
28.400Mhz 1,400W 2,100W

This knobless performance is amazing. Halleluiah, I love Ham Radio.

Overdrive column on the right
The 87A microprocessor can remember custom tune settings by the user. Remember, the processor makes settings for center of segments of the band. The processor's forte is matching the RF characteristics of the sampled RF to similar in it's memory of segments, which it does with speed and repeatability. A human user can tune more accurately than segment matching and save the settings by pressing Enter and then the desired segment (memory position) button within a few seconds.

On 75, 40 and 20 meters I custom tuned with 100 watts drive to produce 2,500 watts output and saved the settings. That is the capacity limit of our wattmeters. I mention this overdrive test so they will be no doubt that the 87A is a bad boy legal limit++ amplifier like the Alpha 99.

I have reproduced the first two paragraphs of this review with answers to the questions.

  • Has Alpha combined a special microprocessor with their amplifier expertise, sans the knobs, and produced a legend? YES.
  • If the Alpha 99 is King of the hill, what could this Alpha be? TOP KING.
  • Most reading this know or talk to some of the guys on the air that use the the 87A. You may have thought, "Why would someone pay that much money for an amplifier?" IT'S WORTH IT.
  • "Does he have too much money to spend?" DOUGH KNOW.
  • "Is the investment rationalized by having the the best answer to the popular on-the-air question - What amplifier are you running?" ABSOLUTELY.

The 87A is the finest Ham Radio linear amplifier this writer has examined, tested, used, fondled or dreamed of, ever. To my knowledge there is nothing to equal this box for serious Ham Radio amplifier fun in any mode, any band. Thank you Alpha. And, the Alphas, including the Top King, return a larger portion of their purchase price used, than any other amplifier.

See all the Alphas at their web site or click their banner ad at the HRM home page.

Our thanks to W5HBO, Frank Noble, Matagorda, TX for the loan of his 87A for this review.
Bob Hutchinson, N5CNN
President and Founder
Wireless Industry Association
713 467-0077


If you would like to publish an article here contact Bob Hutchinson, N5CNN.