Near Legal Limit CW. But Certainly Illegal Capable On SSB.
Bob Hutchinson, N5CNN
I just can't get away from the warm glowing tubes and Winter ain't over til it's over.
So, let's open this "near legal limit" sweetie up, photograph it, put it
together and see if it lights-up. If it does, we'll run it at the WIA bench.
Click Any Picture Larger. >>
Unless I'm missing one, Ameritron makes
four amplifiers utilizing the same compact cabinet: - the AL-800, AL-800H,
AL80B and AL-572. I believe this size is based on the
original AL-80 and
SB-1000 Heathkit. I believe these are all designs developed at Ameritron after
its purchase by MFJ. Here, as we review the AL-572, we will see some
components that apparently are interchangeable and shared by these four
This writer has not opened up the AL-80B, but I suspect it shares the
majority of components. This AL-572 is almost identical inside to the
AL-800H, which I suspect is identical to the AL-800, sans one 3CX-800A7
Eimac tube. These amplifiers appear
to use the same hardware in the RF, rectifier and filter section, T/R,
metering, and tuned input. Different, of course in transformers, B+
voltage, tubes, controls and some dedicated
components. All utilize the full wave voltage doubler
rectifier/capacitor/filter circuit made famous by Heathkit in its classic
utilizes the 3-500Z type tube that requires considerably higher B+ voltage
than the 572B and 3CX800A7 tubes. Because of the high performance of the
3-500z tube in the AL-80B, I suspect the B+ is 3,800 to 3,900 or more VDC.
This commands a plate transformer with about 1,350 VAC available. The
AL-572, AL-800 and 800H utilize the same 2,900 VDC B+ and consequently
about 1,050 VAC from the plate transformer. The AL-800H, with about 1,000
watts more power
output that the others obviously utilizes a healthier plate transformer of
32 lbs. versus about 23 lbs. for the others.
The line up
below is in street price/output power order. Prices are from
The Ham Station in Evansville, IN
and subject to change. Ham friend W5HBO always says,
"it's just function of money".
AL-80B Single 3-500Z Tube ...... $ 1,164.95 QSK-$325.00
AL-572B Four 572B Tubes ........ $ 1,279.95 QSK-$325.00
AL-800 Single 3CX800 Tube ...... $ 1,579.95 QSK-$325.00
AL-800H Two 3CX800 Tubes ...... $ 2,299.95 QSK-$325.00
tube amplifiers, it appears that Ameritron has focused on three box
designs. This box being the middle size, the smaller being the AL-811 AND
AL-811H and the larger being the
AL-82, AL-1200 and AL-1500. Quite a line-up.
OK, it's tent duty
kinda like shooting the AL-800H again. I put the amplifier on the caster
equipped plant stand and worked the Olympus digital and speed lights. At
one point I applied power and made a few shots with the tubes lit
This amplifier arrived with everything in place including the tubes.
Ameritron takes great care in cushioning and wrapping the tubes in their
confined space so they can't be damaged in shipment. Like the AL-800H,
this one arrives with transformer bolted and soldered in. The fuse holders
required the only assembly with the fuses. A complete set of extra cover
screws is included with the amplifier. Nice touch. Nope, I don't believe
any other maker does this. They even send extra screws back with repaired
The same basic parts as the AL-800H. Fiberglass circuit board with RF
coils and taps to the band switch mounted on it. More compatibility of
parts among this middle size amplifier group.
Cooling of the box
And the four warm, glowing 572B tubes are handled like the AL-80B, with a
muffin fan of about 30 CFM capacity. Typical of amplifier design today,
the fan pulls air through the power supply section and blows it through
the tube and plate choke group and exhaust it, and the heat, outside the
box. See Information in another
article about how glass tubes are cooled.
Although not noiseless, this arrangement is considerably less noise than
the centrifugal fan in the AL-800h even though the capacity is the same.
The 3CX-800 indirectly heated cathode type tubes require a pressurized
cooling system to force air through the axial/radial heat exchanger
configuration. Plain old fans don't do that well. Centrifugal blowers will
handle it OK but create more noise and, to me, an irritating frequency
along with the noise. More about this below. Yea, a fix.
the plate choke mounted in the middle of four tubes it serves an ancillary
duty - it acts as a stabilizer to the tubes during shipment. Ameritron
inserts foam packing material around the choke and around the tube and
choke group of components and on top.
Pin diode QSK
I ordered this
Ameritron with the factory installed Pin Diode QSK board installed, it is
not really necessary for normal SSB or semi-break in CW. It is a $325.00,
14% add on option but makes SSB VOX operation silky smooth and VOX delay
can be set to minimum.
and available. You never have to chase down a manual for Ameritron
amplifiers. Just access it at their web site.
The power supply?
It has a multi-purpose
transformer with a little over 1,300 VAC available for the
performance proven voltage doubler HV rectifier/filter circuit introduced
by Heathkit 40 or so years ago. It also provides the ancillary voltages
for bias, metering, QSK, relays, etc. Available, no load, plate B+ is
2,900 VAC. Without this voltage doubler HV power supply
design this amplifier would be considerably heavier and cost more to build
and more to buy. Click Here for more about doubler power supply benefits.
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.
Will this little box
perform? Does it run?
of course it runs. Dollar a watt please.
I went through my systematic load test for the following bands on the dummy load. Drive signal is CW.
Data below is grouped:
Grid Current MA / Plate
Current MA / CW Power Out Watts
Near Legal Limit
In this amplifier
ten meters is enabled by clipping the green wire in the tuned input
circuit area. It looks like a little green worm here.
In CW mode this nice
amplifier is near legal limit. Although we have no way of measuring PEP,
I'm sure it will exceed legal limit in SSB with 100 watts drive. Since
Hams hardly ever exceed the legal limit in this manner, be careful, you
don't want to be one of those, do you? If you want a big legal
limit voice on side band this is a great value, probably the most
legal limit amplifier for your money in the industry today at a - less than $1,300.00
amplifier is quiet. For really quiet operation for SSB use a 12 watt, 200
ohm wire wound variable resistor (rheostat) in series with the fan wiring.
Notice in the picture of the back end of the amplifier a small knob under
the 12 DC RCA connector. Without young perfect ears, amplifier noise with
this arrangement is really hard to detect.
Bob Hutchinson, N5CNN
President and Founder
Wireless Industry Association
If you would like to
publish an article here contact Bob