AMERITRON AL-800H HF AMPLIFIER
Compact powerhouse.
by Bob Hutchinson, N5CNN

OK, OK. I acknowledge that these indirectly heated cathode, metal ceramic jobs have merit even though they don't light up and don't make good heat for winter time use. I was taken with this AL-800H because the marketing materials claim legal + power in a lightweight compact amplifier. Matter-of-fact, it may be the lightest and most compact amplifier in this class, ever.

             Click any picture larger->>

I've been buying from Dan at The Ham Station in Evansville, IN off and on for lotsa years, so I ordered the AL-800H with QSK. Unlike the other amplifier makers, Ameritron prefers to sell through dealers. List price of this Amplifier is $2,545.00 plus $349.00 for the factory installed internal PIN diode QSK board. It appears that Dan's discounted price was $2,299.00 for the amplifier plus $325.00 for the QSK board - $2,625.00 total. It arrived in two weeks.

So, will it live up to claims? We'll show you the inards, the outards and, best of all, we'll see if it runs. Then we can come to conclusions.

Number one box
Open the big box from Brown first, little box later. Ya know, each amplifier maker develops their own methods for protecting the equipment in shipment. Strange - - the maker that has developed the reputation for the economical, lower priced amplifiers has the best shipping and protection-in-shipment scheme, no contest. The Ameritron inter box for the amplifier by it self is equal to or superior to most amplifier boxes and it is totally contain in the outer box. This double box arrangement is very effective. Other makers take notice

With the amplifier on the bench and stripped of it's plastic the small size of the amplifier cannot be overlooked. This is a compact amplifier for the power rating claimed. I remembered that Ameritron puts the fuses inside the amplifier along with an extra complete set of cover screws. Other makers take notice. The layout is standard for most single box amplifiers made today. It's a U shaped pan with front to back divider/stiffener to separate power supply and circuit board section from the RF section.

The Ameritron materials say: 1500+ watts CW or PEP, pair of 3CX800A7 Eimac tube$, the necessary grid protection circuits, three minute warm up, 52 lbs. weight. At the Ameritron web they don't provide the dimensions of this small amplifier but it utilizes the same cabinet as the little brothers AL-800 (1 tube), AL-572,  AL80B and perhaps others I overlooked. Actual measurements by this writer provide a surprise.

• AL-800H  8" Ht. X 14" W. X 14"D. plus front knobs and the tuned input box on rear.
• AL-572    8" Ht. X 14" W. X 14"D. plus front knobs
• AL-80B    8" Ht. X 14" W. X 14"D. plus front knobs
• SB220     8" Ht. X 15" W. X 14"D (Heathkit) plus front knobs.

This amplifier is slightly smaller than the SB220.

Without the cover installed on a modern amplifier the box does not have full structrual strength and everything can flex a lot during handling and movement. This box has a high strength stainless steel bottom pan that provides plenty of stiff. Pressed in PEM nuts throughout.

OK, it's tent duty
So browsers can visit the components inside, it's into the light tent for the photography session. For this fun I set the amplifier box on a house plant dolly with casters so I can rotate it for lotsa shots with the Olympus digital camera. I can lift this amp into the tent even with the transformer already installed. With some, I can only lift up to the 38 inch light tent floor height before I install the transformer.

RF section
A different approach here. The coils are mounted on a fiberglass circuit board with wide flat traces to handle the RF. The band switch appears miniature compared with other amplifiers. It appears to be about the same size as the SB220 switch. The band switch shaft is extended to the switch in the tuned input section mounted outside on the rear of the amplifier. The 3CX800A7 tube requires a tuned input to maintain low input SWR required by today's exciters. Adjustments are handy, if ever needed. Nice velvet smooth 6:1 vernier drives on the Load and Plate capacitors.

Centrifugal squirrel cage type blower
These tubes require it. Glass tubes cool by radiating and conducting heat to the surrounding, air, socket, case and components. These components are cooled by convection. These small metal-ceramic tubes can't get by with that because they cool by radiating and conducting heat directly to the small heat sink fin area which is cooled by convection by lotsa air through the concentrated area. 

Nice quiet muffin or tube axial fans can't cut it here because of the static pressure that must be overcome in the pressurized section of the cooling system. So, the maker has to put enough air through these tubes under pressure to satisfy the demands of the most demanding. Pressurized air capacity, according to the specs is 30 CFM. Today, the designs pull air from outside, through the power supply section, over and around the components and into the fan. Thence, in this case, into the pressurized section, through the tubes and out of the box.

Well, wait just a minute, there. Low power amplifiers have more capacity than 30 CFM with muffin fans. How can this legal limit + amplifier get by with just 30 CFM? It's because this type of amplifier design, using metal ceramic tubes, concentrates the majority of the heat one place, the heat sink fins around the tubes and takes it right out of the amplifier. The manual indicates this is enough capacity to cool things adequately when running 1250 watts CW continuously. Experts say that normal continuous conversation on SSB is only a 15% duty cycle. Believing this, I believe it would be safe to claim that 8 CFM or about 25% of maximum would cool this amplifier for SSB chatter.

Noise?
This amp makes about the same noise as other similar I have tested and a lot less than a couple I have tested or used by Ameritron. A 12 watt rheostat variable wire wound resistor of 0 to 250 ohms variation in the fan power circuit could do wonders for the noise.

Good choking
Big, easy to cool plate choke, huh? The size of a plate choke gives an indication of the power capacity of an amplifier. If it is not right in an air stream it must be large to stay cool and not fry when the demanding are operating or the amp is mis-tuned. This ONE doesn't appear to have any auxiliary cooling facility such as a slot in the air pressure chamber, so big is called for.

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. Ameritron has produced this optional factory installed for some years. I used a AL-572 for a year that had this fine option. Silent and fast.

The Eimac tubes
Most amplifier makers now install Russian and Chinese tubes in their amplifiers. Ameritron uses imported tubes in other amplifiers but have stuck with Eimac in this type and style of tube. This tube has an excellent track record of performance and longevity. Economics may require that they revisit the 4CX800 type tube as it is about 20% of the cost of the Eimac.

Amplifier Designer Tom Rauch
When I decided on moving this amplifier up in the review schedule I had a nice conversation with Ameritron amplifier designer Tom Rauch. He has been designing and building the Ameritrons for years. Obviously, he must be doing it right as Ameritron sells more amplifiers than all the other U.S. manufacturers combined. Even with the highly popular and economical  Russian 4CX800 tetrode showing up in competitive brands, Tom says he will continue to utilize the 3CX800A7 Eimac triode because of its superior specs. and wonderful track record. I suspect he will stay with the Eimacs until economics force him to seek change.

The manual
Complete with diagrams and schematics showing components. The manual is also available on line. Click Here.

And the power supplies?
It has the time and performance proven voltage doubler HV rectifier/filter circuit introduced by Heathkit 40 or so years ago. Without this voltage doubler power supply design this amplifier would be considerably heavier and cost more to build and more to buy.

It's not the wind, its the wind for reducing the weight
Most amps today have one of these two types of HV power supplies:

The circuit board area includes the full wave rectifier/filter/doubler circuit, meter, 50K bleeder resistors and control circuits and components. The full wave rectifier circuit utilizes two five diode strings of the industry standard N5408, 3 A., 1000 PIV type. The picture shows four diodes standing up and there are six more mounted in a flat position.

The doubler filter section is populated with typical computer grade electrolytic capacitors totaling 63 mfd capacity.  The no load B+ voltage is specified at 2600 VDC. Our actual test measurement was 2613 VDC. Pretty close, huh? It sags to 2250 at full load.

Some assembly required
Ha! Guess what? This amplifier comes with the transformer bolted and soldered in. A wide range of mains voltages can be used as it is rich in primary windings. Unlike any other amplifier in this class, input voltage arrangements are changed with the soldering iron. See pictures.

The only install needed is the pair of Eimac 3CX800s and two fuses. I was surprised to see the threat of voided or nullified warranty on the tube boxes. These babies are now in the $500.00 range - each, and the manufacturer's warranty may go away if you don't return them in THIS box only? I think, with this attitude of distain for the customer - Eimac, in the Ham Radio market, may go away as their warranty may. Their original packing material is just small bubble wrap. No big deal.

Dense
I am always surprised when I handle a metal ceramic tube because they look light and are actually heavy because of the ceramic and steel. The outer ring and fins are aluminum or non ferrous alloy. I removed the chimneys, carefully inserted the shinny Eimacs, without pin mishap, slipped the chimneys properly over the tubes and attached the connectors to the anodes. The cover fits great. The fuses fit OK too.

Will this little box perform? Does it run?
It lights up! But, only partially, the grid and plate ampere meter light doesn't light up. Bummer for a new amplifier. Oh! It came on. This meter lamp double as the three minute, ready lamp. Comes on after the indirect cathode heaters have heated indirectly.

Bench
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.

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
 

Band	QRP Settings Column 50W. Drive Grid/Plate/Power	Loafing Column 70W. Drive Grid/Plate/Power	Bad Boy Column 100W. Drive Grid/Plate/Power
1.90 Mhz	20/850/1,150W	25/1150/1,400W	65/1400/2,000W
3.90  Mhz	25/850/1,300W	35/1000/1,500W	65/1400/2,300W
7.200 Mhz	20/850/1,200W	35/1150/1,750W	50/1425/2,250W
14.225 Mhz	25/850/1,450W	35/1000/1,800W	50/1450/2,400W
18.140 Mhz	20/900/1,400W	35/1000/1,800W	50/1500/2,400W
21.350Mhz	20/1100/1,500W	35/1300/1,800W	50/1450/2,150W
	Ten meters not enabled on this amplifier yet.

Over drive column on the right
About 60 watts will drive this little powerhouse to legal limit on 80m, 75m and 40m. Only 50 watts need on higher frequencies. This sweet little box is a little loafer at legal limit. For you bad-boy wantabees, the AL-800H is just loafing at 1,500 watts CW output.  I continued tuning on the dummy load in short segments and increasing drive until full output of the 100 watt exciter was reached. As I was working up to maximum drive I raised the drive just a few watts from 50 and keyed, the nice grid overload protection circuit would shut the amp down. A flip to standby and then back to ready resets the protection circuit.

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