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Ameritron AL-811 Review | Radioaficion Ham Radio

Ameritron AL-811 Review

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Ameritron AL-811 Linear Amplifier

Get the real thing at the right price.

In the world of linear amplifiers, only one I factor seems to be emphasized: cost. The higher the cost, the better the amplifier. And the better the amplifier, the better the signal. Hmm, the latter is an interesting premise, but not necessarily true.

The object of a linear amplifier is to increase the RF output of your station. In simple terms, to increase (he talk power. When figuring power increases, you must be aware of a general understanding among radio operators—the law of decibels.

Let's take a typical 100 watt PEP exciter (the average modern transceiver output) and double the power. The new output of 200 watts is an example of 3 dB gain. This gain represents what is considered a noticeable received signal increase, attained every time the power is doubted. This, doubled to 400 watts, makes a total gain of 6 dB: 800 watts, a gain of 9 dB; 1600 watts, a gain of 12 dB. Of course, the FCC limits power out to 1500 watts, but we won't split hairs over the extra one hundred watts for this paper exercise.

 

You can see from the example that the greatest gains are at the lower watt end of the scale. What, you ask, does this have to do with a review of a linear amplifier? Simple economics! It is much less expensive to attain a 9 dB gain than a 12 dB gain. In fact, going from 100 watts to 800 watts will be less expensive than going from 800 to 1600 watts The power supply can be smaller, the tube(s) cheaper, and the internal components need not be as heavy.

Today I feel it is safe to say that you will usually spend a minimum of a thousand dollars for an amplifier that produces a 9 dB gain, and twice that for the remaining 3 dB.

With the introduction of the AL-811 amplifier, it's refreshing to see a quality amplifier for under $600.

review Ameritron AL-811 Linear Amplifier

Installation

The AL-811 comes in a double box, well-designed to protect the amplifier shipped inside. This amplifier looks like an amplifier: The case is large and the controls are not the sub-mini size we are used to on our imported rigs, The two front panel meters are well-lighted and easily read. One meter displays either high voltage (HV) or plate current (Ip), the other monitors the grid current at all times. A red LED indicates key-down, and a standby switch is included on the front panel.

Inside the AL-811 you will find three 811 As in a grounded grid arrangement. This is an old and well-proven tube design, originally developed for use in RF. They are capable of handling considerable abuse at the hands of hams lacking tuning expertise. In the event of failure they are readily available for about $25 each. This is considerably less than even the 3-500Z, which now goes for well over a hundred dollars.

To prepare the unit for operation, just remove the cover's screws and lift it off. Inside you will find plastic foam around the tubes and a bag containing the neatest fuse holders and fuses I' ve seen recently (they push in and pop out; they're not the old screw-in type). After removing these materials and checking the tubes and other components for security, I replaced the cover, installed the fuses, and hooked the amplifier up.

While inside the unit, I took note of the very nice glass epoxy circuit boards, excellent structural design, and quality of workmanship. All was top grade. Unlike many amplifiers I have examined over the years, the chassis of the AL-811 does not use the cover as an integral part of the chassis (stiffener). It is just a cover, and no more.

The RF input circuit is a very solidly built Pi-network tuned slug system. The Pi-network output circuit is of equal quality. The power transformer connections, using a buck boost winding, can be changed lo accommodate 120/110/100/240/230/220 VAC, making it workable nearly anywhere.

review Ameritron AL-811 Linear Amplifier

An ALC circuit is built into the AL-811 to prevent excessive drive levels from damaging the amplifier, and to prevent the resulting RF interference it causes,

Observations

For the sake of safety, and for the edification of the many hams who have never operated anything using more than 12 VDC in the power supply, Ameritron has included internal and external labels warning of the lethal voltages present within the amplifier.

The instruction manual is short and to the point, I would advise anyone using the amplifier to read it before turning anything on. Included with the manual is a one-page generic set of instructions for tuning all linear amplifiers. This fine page should be read by all using, or contemplating using, an amplifier, as it answers many questions you might ask,

I noticed some contradictions in the manual involving input power. Depending on where you look, you might see a "never exceed" limit of 70, 85, or 100 watts. For the purposes of this evaluation I chose the latter, as that was the power mentioned in the tune-up section.

Ameritron's one-year product warranty does not appear to include the tubes No mention of warranty on the tubes was seen.

Using the AL-811

The AL-811 comes from the factory set up for 120 VAC. As the current draw is not high (max. of 8 A), you may not need to do any extra wiring to use the amp. This will depend upon your house or shack wiring. I can tell you, however, that if you locate the amp over fifty feet away from your circuit breaker box on a #14 fine, you will experience a significant voltage drop during key-down.

My recommendation for this, or any RF amplifier, is to operate it on a circuit of its own. Plug-in power bars, although nice for powering small equipment, are not satisfactory for powering an amplifier, (See the table.)

Watching the output signal on my scope, I saw no bad news. The signal never flat-topped. In getting signal reports, I switched between the AL-811 {700 watts) and my AL-80A (900 watts). In some cases I told the receiving station what I was testing, while in other cases I kept the station in the blind. There was never a time when the AL-80A was reported better than the AL-811. Reports were "no change seen," as expected.

Due to the law of decibels, as described earlier in this article, the difference of a couple of hundred watts won't be noticed at the receiving point. Of course, you could spend another thousand dollars and get a "full power" amplifier to get that last 3 dB.

review Ameritron AL-811 Linear Amplifier

The Judgment

What I liked the most about the AL-811 included the stout chassis, inexpensive tubes, quiet fan operation (my computer makes more noise), excellent internal construction, and the 12 VDC keying circuit.

My dislikes were few. It would be nice, for example, if the meters were slightly larger. Also, I found some mistakes in the manual.

Do I recommend this amplifier to other hams? Very much so! It is cost effective, something you rarely see in ham radio these days.

- 1991 Bill Clarke WA4BLC - 73 Amateur Radio Today - fotos by ai4w

review Ameritron AL-811 Linear Amplifierreview Ameritron AL-811 Linear Amplifier

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