Ameritron AL-80B

more power to ya!

© 2018 by KV5R. All Rights Reserved. Rev. 3/18/2021.

(Jump to Tuning Up the AL-80B)


There comes a time in every hobby where we have to decide to either back out of it or get serious. Frankly, I’ve always resented the idea of having to spend a bunch of money just to overcome someone else’s noise problem, but the fact is that most people don’t want to talk to you if they can’t hear you well. That’s just the way it is. I ran barefoot (100 watts) for twenty years, with the convenience of an auto-tuner and push-button tuning. But recently I realized it was time to move up and as they say, run with big dogs. We are currently in the low part of the 11-year sunspot cycle, and most of the HF activity is on 75 meters — and 75 is a very noisy band, especially in the summer. When the distant storms are running S9+10, you need to be at least +15 or 20 if you expect to be heard.

I studied the situation for a few weeks, and finally settled on the Ameritron AL-80B amplifier. It easily runs about 800 watts PEP, using a single 3-500ZG tube. I read all the articles and reviews about it; it’s well-designed, reliable, and a good dollar-per-watt value. Everybody that has one loves it. Running a nominal 800 watts is 9dB (1½ S-units) above barefoot, and less than 3dB below the full US legal limit of 1500 watts—at about one-third the price. Sure, I’d rather have a solid-state KW and a high-power auto-tuner, but that option runs about 4 grand, and I determined to spend well under 2 for this upgrade.

I also considered the ALS-500M and the AL-811H, both of which are around $500 less than the AL-80B. But with the -500M you still have to add a 75 amp power supply, which is several hundred dollars more, and then you have a 500 watt amp that cost almost as much as the -80B. The -811H, called an 800 watt amp, is really 600, has flimsy 811 tubes that like to pop, and has no RF power meter. I did not consider the ALS-600, because it’s just way too darn expensive for 600 watts; and the -1306 even more-so. So in the end, I stand by what many others say, that the AL-80B is the best value per watt in new HF linear amplifiers. And I got it on sale for $1425 (GigaParts, no tax, free shipping), which is well below the normal $1645+shipping retail price.

Since I run a multi-band ladder line-fed dipole, and my auto-tuner is rated at 300 watts, I also purchased an MFJ-989D, their largest antenna tuner. It’s actually quite a bargain, considering that it also provides active peak-reading meters, antenna switch, a big current balun, and a dummy load, in addition to a legal-limit roller-inductor tuner. Yes, there are better antenna tuners, but only at twice the price.

Please enjoy my little “QRO Day” story in pictures. After the pictures I’ll discuss amp tuning & operating.


“Something strange is coming… I don’t recognize that sound…”

Yay! The wait is over.

Let’s both carry that 55-pound box…

The larger one, containing the tuner and the tube, is much lighter.

Two big boxes—now the work begins…

GigaParts shipped the tube in the big box with the 989D tuner, and it was double-boxed and well-padded in foam rubber.

The business-end of this project, the Taylor 3-500ZG tube (yes, it’s a China tube, they all are now). Just think, there’s 14.7 pounds of air on every square inch of that glass! An implosion would ruin your day, so handle with extreme care. I unpacked it on the bed, and left it there until installed.

MFJ-989D, Versa Tuner V, legal-limit antenna tuner. It also has active peak-reading meters, antenna switch, 1:1 bifilar-wound current balun, and dummy load, which if purchased separately would cost as much as this tuner. I did have to do two minor repairs, which we’ll see in another article.

Tuner’s rear panel, with connections for 2 coaxes, long-wire, and balanced feed line.

The new tuner goes under the 7100 and 993, since the AL-80B will occupy the other side of the little table. I should have opened it up and inspected it, because a few days later I discovered the turns counter was slipping and I had to pull it out of there a do a little alignment on the gears (see article). Later, I ended up putting the tuner on top of the amp, because it’s just too hard to get to the back of everything in this corner.

And there it is. Time to open it up, inspect it, and install the tube. An RF amp may be the only piece of electronics where the first thing you do is remove the cover. Never ship an amp with the tubes installed!

Rear panel input tuning slugs. Hopefully they will not need adjustment (the 15/17 did).

Input, output, keying relay jack, ALC jack, 12V accessory jack, and ALC limit control. The fuse holders are near the power cord.

Amps are hand-made, so carefully inspect it for any loose hardware or bad solder connections. The plate cap is wrapped and taped down, and the fuses are in a little package. Everything that I could check was tight, and the soldering looked good. I took a bunch of extra pictures of the insides for future reference.

The high-voltage plate cap, which is also a heat-sink to cool the tube’s anode connection.

I guess this is what passes for tube sockets nowadays. I was expecting a ceramic socket, but oh well, as long as it works… Notice the pin arrangement: there are 4 in a half-circle, and 1 by itself.

Carefully install that $220 glass thang. The manual cautions to not twist or rock it, just line up the pins and push straight down. As it spread the contacts, it landed with a surprising thump, so it might be better to put a finger under it next time.

Attach the plate cap and snug its set-screw. The manual cautions to not over-tighten it. Just snug. Be very careful here! Just having that screwdriver that close to that high-vacuum glass envelope made me nervous! That’s just for the photo; when I actually tightened the screw I had my other hand under the plate cap and screwdriver.

Years later, I’ll know when it was put in service. Always date your tubes.

Install the 2 fuses in the rear panel sockets.

Switches off.

Put meter in HV position.

Connect cables. See also my homebrew amp interface article.

Plug it in already! I put in a dedicated 20 amp circuit for it. #12 AWG cable from breaker panel to 20-amp duplex receptacle. The -80B will draw about 12 amps at 120 volts at full output. It can be re-wired for 240, but with a dedicated circuit it should not be necessary (it wasn’t). If your outlet can run a 1500-watt space heater, it’ll run the -80B just fine on 120 volts, unless you have a very long wiring run. At greater than 50 feet, I’d either switch it to 240, or run #10 wire.

Switch on! No smoke, no pops, just a hair under 3200 volts, exactly what it should be. Yay! It’s alive! By the way, the forward and reflected meters are active peak-reading meters, so you see real PEP, not average, when running SSB voice. And it’s a fast-acting peak meter, not the old slow capacitor-discharge type.

The filament works, too.

And there it all is, in position, and ready to put big signals on some new friends’ meters!

Tuning Up the AL-80B

There are two distinct types of "tuning up": (1) Initial Load Discovery, performed only once per frequency; and (2) Normal day-to-day tune-up, after a QSY. The purpose of (1) is to determine and chart the proper LOAD setting for each frequency. The purpose of (2) is to set the Load to the previously charted position, then key up and peak the Plate.

Initial Load Discovery

Tuning a high-power tube amp is no simple matter for newbies. An out-of-tune amp generates excess heat and burns up expensive things, as well as producing splatter. I found that reading and following the manual didn’t really give me a good feeling for the whole tuning process, so I went on-line and quickly located lots of opinions about how to tune an RF amplifier. Still not satisfied, I then discovered the writings of W8JI, who just happens to be the designer of Ameritron amps. That’s good info, and I finally got a good idea of how an amp should be properly loaded, not from sundry opinions, but from the guy who designed it.

NOTE: When I cite power levels, that is RF power meter into a 50-ohm non-inductive load. Typical RF power meters are HIGHLY INACCURATE unless the load is 50+j0 (1:1 SWR). So for example, if I say “set drive power to 60 watts,” that means bypass the amp and switch to dummy load. The SWR INTO the amp may be 1.5:1, and your input meter reading will be way off when you put the amp on-line!

The two controls, Plate and Load, are interactive, but they each act very differently, and must be understood:

  • The Plate control must always be peaked (max RF output), as it resonates the tube’s output circuit. It has a specific peak point for every frequency and Load position, but it does not vary with drive power. Exact setting of the Plate control is much more critical than the Load setting. It must always be peaked! Note that some people say “dip the plate current,” because it happens that at output power peak, the plate current dips a little bit. You can do it either way, since the AL-80B has meters for both.
  • The Load control determines the coupling between the tube and the output. It is dependent on both frequency and drive power level. It cannot be accurately set at low power, but must be set at for peak at slightly above normal drive power, then left there as the drive power is reduced to the normal operating level, which is around 50-60 watts in, and 700-800 watts out, for the AL-80B.
  • Since the controls interact, the Plate must be peaked after every move of the Load.

A Load Coupling Analogy: Imagine your car, with a manual transmission, in first gear, floored — engine over-revvs! It’s under-coupled to the load. Or in 4th gear, going slow — engine under-revvs, power is low, but cylinder pressure is way too high, egnine knocks, etc. It’s over-coupled. But in the right gear for the given load condition, the engine runs near peak efficiency, and everything goes along fine. An amplifier that’s under-coupled swings its plate voltage too far, clipping at 0 volts, and peaking high enough to arc the tube. Increasing the load coupling keeps the tube from “over-revving,” but over-coupling too much makes the current go way up, like the over-pressured cylinders in a slow car in high gear. So we can think of the Load control as something like a variable transmission in a car, matching the engine (tube impedance) to the wheels (output impedance).

The most important meter indication to watch is the grid current. An under-coupled and/or over-driven amp will have high grid current, which will quickly (in a few seconds) destroy the tube. One high grid current accident will cost you a cool $220. So read the manual, and W8JI’s articles, and keep your grid current down in the safe range, at all times. The maximum continuous grid current rating for the 3-500ZG is 120 milliamps, but for very brief max-power tune-ups, 160mA probably will not destroy it, but 200mA will. The manual says 180mA is the “never-exceed, even very briefly, limit.” The Load setting, as well as drive level, will control the grid current. My amp, properly loaded and driven to about 775 watts, will run the grid at about 130mA, and the plate current at about 380mA. Remember that that number is seen accurately only with a steady carrier, not voice, as the grid current meter shows average, not peak current. So, you tune up and see 130ma, but then talking you only see maybe 80ma. Nevertheless, the voice peaks (not seen) are hitting 130ma, but it’s very short duration, low-duty-cycle peaks.

For this Load Discovery process, I recommend driving the amp to about 800 at the best Load setting (always peak the Plate), then reduce drive power to produce about 775 for normal operation. Please don’t simply take my numbers as absolute, but carefully get to know your own tube. I have found that, on mine, around 130-140mA grid, and 375-400mA plate, produces 775-825 watts. A more conservative setting is 50 watts drive, 120mA grid, 375mA plate, for a bit over 700 watts. Pushing it to 900 watts puts the grid current well into the danger zone. Ameritron can call it a 1kW amp all they want to, but running it that hard will surely shorten tube life, and there’s no margin for error.

NOTE: Make a Tuning Chart: Best way is to use MS Word or OpenOffice Writer to make a grid chart on the computer. I made columns for Freq; Tuner: Trans, Ant, Induct; Amp: Plate, Load; Readings: Ig (grid current), Ip (plate current), and Output Power. Print several pages and fill in with a pencil as you go. After some experience, you’ll find better numbers, so erase and record them as needed.

Finding the Load setting, at “max”max power, must be done in several very short tests, 3-5 seconds on, 15-20 seconds off. This process is sometimes called “load discovery,” where we discover where the Load should be set for a given frequency. We then make a chart of settings and return to them for subsequent operations, at a slightly lower drive power. The manual gives suggested initial Plate and Load settings, but you still have to determine your own, because each tube is a little different. On my amp, the proper load settings are much lower than the manual!

You can’t just key down and twist the Plate and Load for peak power and be done, because the Load affects the Plate. Instead, the Load is stepped along little by little (one mark or half a mark on the dial), and each time the Load is moved, key it and quickly re-peak the Plate and note the output power and grid current. After several such tests, an optimum setting will be found for the Load, which will be peak output power — but keep the grid current in the safe zone by reducing drive power, if needed. As the Load gets close to perfect, the tube efficiency goes up and you need less drive.

This is repeated at several frequencies across each band, and recorded in your chart. If you’ve never done it before, it takes all day to find settings for several frequencies on all the bands. Take your time, and watch the tube’s anode color. If it’s getting orange, slow down, decrease your on-time and increase your off-time. A dull red glow is okay, but orange is getting too hot. You also need to watch your dummy load temperature and stay below its duty cycle spec, which is usually 10-20%.

NOTE: About "max" drive power: The manual says to find the load setting at maximum drive power, which for most radios is 100 watts. I disagree. Dumping 100 watts into a single 3-500Z is ALWAYS a BAD idea! In the following discussion, "max" is a little above "normal" drive power. I consider 60-65 watts (read into a dummy load) to be "max", and 50-60 watts drive to be "normal" for this amp, when properly tuned.

Most tuning instructions say to reduce your drive power to a very low level, tune up, then increase it a little and tune up again, and so on, until you reach your "maximum" power (or max grid current). That’s a good idea if you have no idea where the Plate and Load should be to start with, but if you start with them at the Manual’s settings, and peak the Plate at low power, then you can go straight to "max" power (as described above) and commence the Load Discovery process. But if you feel better sneaking up on it, by all means do so, at least the first time, per band.

The reason the Load position must be determined at “max” power is that, as stated above, the Load position is dependant on the power level (the impedance of the tube changes with power). For example, your Load (on 80 meters) might be best at 2.25 when driving the amp to 800 watts, but at 1.25 when driving it to 500 watts. The problem is that if you use a Load position for 500 watts, then drive the amp higher, it will be “under-coupled” and non-linear, have high grid current, and produce splatter (the plate voltage swings too far and clips at 0 volts). So the Load position is determined at “max” power, then left there for operation at “normal” power, so it’s always slightly over-coupled. This ensures that the amp is never driven into non-linearity, or hits an excessive grid current level. Being a bit over-coupled is always better than being under-coupled. Also, if the Load is set way too low, the tube will arc internally and blow a hole in the grid, so always err toward a higher Load setting. Furthermore, severe under-coupling can arc your tuning capacitors, which leaves rough spots on them that will easily arc again. Severely over-coupling will cause things to get hot in a hurry, as the voltage swing is low and the current swing is high.

Once Load discovery is done and the settings are recorded in a chart, you shouldn’t need to do that max-power Load discovery thing again (until you change the tube). Do your Load discovery into a dummy load, and then always operate into a 50-Ohm load (tuner tuned to flat SWR), and your Load settings will be right, provided you determined them at "max" power. How many Load settings do you need to determine? I don’t really know, but I recorded a Load (and Plate) setting every 25 kHz across every band. After using it a while, I think every 50 kHz would be sufficient, as you can easily interpolate for in-between settings. The bandwith for Load settings is fairly wide, but the bandwidth for Plate settings is very narrow. But the more data points you have in your chart, the closer your settings will be before you even hit the key. You’ll then set the Plate and Load according to the chart, then briefly key up and peak the Plate, which can be done at low or normal operating power. But remember: Never peak the LOAD at reduced power! Use the charted setting you determined at "max" power.

Normal Daily Operation - How I Do It After QSY

All the foregoing has been just to determine Load settings and develop a chart. Once that's done, a QSY tune-up is a simple matter.

  1. Power up the amp and check the BAND switch and STBY (standby) switch.
  2. Check the frequency and do not QRM. On LSB move 1kHz above, and on USB 1kHz below, the active QSO. That puts your carrier in their opposite sideband, where it will be suppressed. But make sure you’re not 1kHz into an adjacent QSO! A panadapter is really handy here.
  3. Set radio to RTTY, and set output to about 55-60 watts (for an AL-80B). Or you can leave the radio at full output but reduce its power with the ALC feedback loop from the amplifier. I prefer to keep my radio at 60, then set the ALC on the amp to reduce it just a tiny bit more. This ensures that the amp is never over-driven, as ALC bias is asserted both from the radio and the amp.
  4. Key the radio and tune the antenna tuner to a flat 1:1 SWR. You should also have tuner settings in your chart, so you are very close before transmitting. ALWAYS set your tuner at low (barefoot) power! And do NOT switch or roll the inductor while transmitting more than just a few watts!
  5. Set the Plate and Load controls to the chart, as previously determined at "max" output, for the current frequency.
  6. Put the amp on-line (switch to Operate).
  7. Key the radio and amp and quickly peak the Plate. It is more sensitive than the Load control, so you can’t just use the chart setting. The Load, however, will be fine as set by the chart.
  8. Briefly key once again and check output power and grid current, just to make sure everything is nominal.
  9. Switch to SSB and operate!

Other Considerations

It always sounds (and reads) a lot more complicated than it is, but after a little while it becomes second-nature, and is no more difficult than unlocking your car, getting in, cranking up, and driving away without crashing. You follow a procedure, develop habits, then do it the same way every time.

Remember that driving any amp to its maximum is a bad idea. Others will not see or hear any difference between 750 and 1000 watts, so do your tube a favor and run it 20-30% below its maximum possible output. As they say, if your car will do 120 MPH, would you drive that fast all the time? But people buy an amp that says 1,000 Watts in the ads, and expect to run it at 1,000 watts forever! 750-800 is a good speed limit for the AL-80B, and that’s only half an S-unit (and $2500) below legal limit.

Another thing to consider is duty cycle. If an amp will comfortably do 800 watts on SSB voice peaks, that’s a light duty cycle. Running a higher duty cycle mode, like CW, requires a reduction in power (500 watts), and running a very high (100%) duty cycle (RTTY) requires a further reduction, to well under 400 watts. For AM, the AL-80B manual says do not exceed 200 watts carrier power.

NEVER reduce power by de-tuning the amp! Reduce the radio output, either with the radio’s RF Power control, or the ALC on the amplifier, or both.

About ALC: You may hear some hams saying they never connect ALC. That’s just plain stupid! Connecting and using the amp’s ALC allows the amp to control the radio, and thus protect itself from over-drive. Even if you don’t want any ALC action from the amp, you can set it right above your normal operating output level and it’ll be there to protect the amp if you accidently transmit with the radio at full output.


After a couple years of use, I’m very happy with the AL-80B. It’s a workhorse, is well-designed, and once that Load Discovery bit is done, very easy to use. I wish it was a solid-state amp, but it’s around $2000 less than an ALS-1306, so I don’t mind twisting knobs occasionally. The only thing I don’t like about it is it’s big and heavy!

On-air reports are good; when switching it on, the signal goes way up, with no distortion or change of audio quality, just as it should. Also, I have recently built an RF current sampler and connected it to my oscilloscope, and the signal is nice and clean.

Please see the other articles in this series, where I added an I.F. panadapter to the 7100, built an amplifier interface, a salt-water dummy load, and repaired the 989D.

Next, we’ll look at some accessories you can build for your amp, and save some money.

73, — KV5R

33 thoughts on “Ameritron AL-80B
  1. Thanks for all of the excellent tips and procedures! I have a situation that I could not find listed above. Depending upon the frequency, I have major differences in output power. On 160, I can get about 700 watts. It goes down from there to about 250 on 10M. Any thoughts?

    • Howdy Bill,
      Can’t say, without details.
      If you’re loading properly (a bit higher than peak output, after peaking the plate each time), and getting proper grid & plate current readings, low output on the upper bands means either your drive power is lower, or your power meter is deceptive, or your burning something up (real power gotta go somewhere).
      If the inputs are mis-tuned and you have high swr into the amp, your radio might fold back power.
      Meters are only accurate into 50 ohms, where they are calibrated to. You can’t read your input power into the amp, because the amp’s input matching network is never flat, typically 1.5-ish, which throws your meter way off. Gotta set drive power into a dummy load, then put the amp online. 50-55w, not over 60w, for the 80B.
      125-135ma grid, 350-400ma plate, should give 700-800 watts (carrier), and if the amp’s tuned right, 20-30 seconds of that will only begin to glow (dull red) the lower end of the tube’s anode. If something’s wrong with the tuning (and/or failing parts), the tube will either arc internally (“tink!”), or glow in a big hurry! And/or other parts will arc (usually load/plate caps) or melt (usually band-switch or chokes).
      I’d suggest tuning up and testing at a very low drive level to determine the power discrepancy. If your tuning is right but still get falling power, then open it up and look for overheated parts. Remember a load setting at low drive power will be badly under-coupled at higher drive power, and must be re-done when increasing drive.
      After you’ve collected some test details, you might contact Ameritron, or W8JI, for better answers. My understanding of such things is just passable, not expert!
      73, —kv5r

  2. I have an issue with my AL-80B and after reading your website would appreciate your input! Using the AL-80B with my IC-7300. When I got the amp about a year ago it worked fine, always loading up nicely and I usually always ran it for output power of 700 to 750 watts. About a month ago all of a sudden all band settings drastically changed. My load were per factory settings or within 5% or so with the plate only differing slightly. One day turned it on and it wouldn’t load at all with those setting so used your load determining procedure and found that it would load but at dramatically different settings. For example, 40 meters was fine at plate 7 and load 4.5 with 700 or better output if I wanted to go that high and all of the other load settings for other bands changed as well. Plus, max output power on any band was 200 to 300 watts less. My SWR output settings from the 7300 to the amp were all 1.2 to 1.4:1, but after the problem occurred now when I key the amp the SWR on the 7300 jumps up to near 2 to 1 which had not previously occurred. If I run the 7300 straight through the amp while it is off or on standby all is fine with low SWR and 100 Watts output on all bands. I would love your opinion based on this description if it is just the final that may have gone bad or possibly something else as well. Also, since I suspect there may be other issues I still may want to replace the final 30500Z. I see them offered for sale but most are a newer model with a ZG after it – can I use that designation type of tube! Thank You, Frank K1EBY

    • Howdy Frank,
      With both input and output impedances suddenly changing, and on all bands, it’s likely the tube has flashed over inside or something. Or maybe a toasted plate choke or grid resistors, I donno.
      Check plate voltage supply meter, too. Normal is 3-3.2kV idle, ~2.7-3 under load. A failing HV supply will both lower the power and change the tube’s internal impedance, so the output load setting and input SWR will change.
      Yes, all new ones are “ZG”, G for graphite anode. RF parts has them for about $220, and they say the recent runs of China tubes are much more reliable than a few years ago.
      73, –kv5r

    • You cant wipe out filament in an instant, that is a at least a semi-gradual process even when due to positive ion surface poisoning caused by pushing the filament to its emission limit . .

      Does this one have the dynamic bias circuit ?

      Flashover can damage the grid resistors ( some are, sadly, direct grounded) also can damage the grid current metering shunt (safety rectifiers to chassis on the cathode return a good idea)

      It can also damage the dynamic cathode bias . .

      If the fil grid bias is no longer fixed due to fault in dynamic bias / grid resistors / meter shunt / cooked grid trip circuit shunt

      allowing the cathode grid voltage move positive adding negative grid bias under current.

      tube input impedance increases causing the input match to go off,

      no ability to overcome the tube self biasing to cutoff, pulling less anode current,

      which affects plate load setting to adapt to the new higher plate impedance that corresponds to the reduced anode current.

      Check the grid resistors (if they are there) and the meter shunts . .

      For a test, you can ground the fil transformer center tap to chassis ( cathode return , and will disable grid meter )

      bypasses the dynamic bias, grid limiter, ( and the tube will pull current even in standby )

      returns the tube to a solid zero bias, to see if the tube will perform with the fault bypassed

      return to your old load setting, tickle it with low power to find plate resonance and run your drive up to the old setting

      input swr should go back to normal too .

      At least then you will have some idea where to look.

      • Btw . . if you have poisoned the filament . . leave the tube lit for a week with the HI-V disconnected/disabled (pull and cap the transformer hi voltage leads)

        The idea is to allow fresh emissive thorium mixed in the tungsten to migrate to the cathode/filament surface to regain emission.

        (a gradual process that happens over the life of the tube, finally going flat when the supply of thorium is depleted)

        If successful, dont push tube to its cath-emission limits which will poison it again.

        ( the unused electron cloud surrounding the filament protects the emissive thorium from being altered by positive ions generated on the anode, which are normally intercepted by the unused filament emission.

        Thorium that has had its charge altered by the addition of those positive ions maintains a tight grip on its electrons after that.. the tube filament looses emission leaving it ever more vulnerable to further poisoning.
        its a death spiral.

  3. soy la xe2 egi eliazer garcia y tengo el anplificador ameritron al-80b pero seme ase conplicado como tuniarlo por fabor mandame un bideo para aber como trabaja

  4. may 2nd 2022….just bought a 80B, after reading this thread i realize the mfj manual is confusing..?
    I have the over grid protection mod…any one out there installed this modification..?

  5. “About ALC: You may hear some hams saying they never connect ALC,” (like MFJ says) “to do. That’s just plain stupid!” Funny that MFJ says don’t use ALC on their amps. Also, “rear panel input tuning slugs. Hopefully they will not need adjustment (the 15/17 did).” MFJ told me never adjust the rear slugs. Why and what did you need to adjust and what test gear did you use to see what changes you were making; I assume all was done with no AC power.
    Finally, this is what goofs everyone up: the Ameritron/MFJ instructions are horrific. Why does MFJ say to excite the amp (AL-811) with 60 – 80 even 100 Watts to first tune the (AL-811) Amp and 100+ Watts for the AL-811H and more for AL-80B? That puts Grid Current over 150 mA and instructions say not to exceed 150 but tune with up to 200mA. Then, MFJ tell me never use more than 20 to 30 watts to tune and that’s all ____ at MFJ/Ameritron uses. Anyway, my 811 is a fine amp and I did get the AL-80B and picked up Tom’s W8JI TOF units for the 80B.

    • I’ve never seen Ameritron say to not use ALC. SSB always has overshoot and without ALC that will make splatter. Look at a waterfall, you’ll see who’s not using ALC.
      The input tuning slugs are adjusted for minimum SWR going into the amp, and are adjusted at normal drive power, with the amp all tuned up, at the middle of each band. They usually bottom out at about 1.5:1 but are very broad. I tuned the 17/15 meter slug a bit so it would favor 17, which I use a lot more often than 15.
      Yes, the Ameritron manuals confuse a lot of people. Pushing 100 watts into an 811 or an 80B will likely blow the grids. Load discovery should be made, for each band, at slightly above normal drive power, so it ends up being slightly over-coupled. For the 80B, that’s around 60 watts. I don’t know about the 811, but it will be what drive power, when properly tuned up, gives about 450 on the 811 or 600 on the -H, which I hear should be considered “max” for those amps.
      73, –kv5r

  6. about al 80b amp

    let me teach

    I am in trouble with that
    when I point to ALC set on the front penel,
    in my case needle Shake off
    How to fix

    I want to buy ameriton AL80B meter lamp for replacing
    Let me know How to order
    also I wonder no right on the meter first of all

  7. I had an AL-82 and sold it. Dummy me! I managed to pick up an AL-80b (used but pristine condition) and have yet to use it. Quite frankly, I’m not sure how to use it. I have an ICOM-7300 (new) and I’m scared I’ll ruin my radio. I have the interface from MFJ. Anyway, maybe someday I’ll figure it out. It’s a rugged amp. I’m gun shy because I had a friend who fried another amp while trying to tune it up.

    • Howdy Don,
      It’ll tune up with same procedure as the -82 or any grounded-grid tube amp.
      Practice a tune-up at low power, maybe 5-10 watts drive, until you are comfortable with finding the best load setting. Peak the plate each time and note the grid current and output power. Unkey. Move the load a little, key, peak plate, take readings, unkey. Quickly! It’s a cycle; repeat until max power is found.
      Make a chart of the settings: freq, drive power, plate, load, grid, output. Making a chart keeps you off the key longer!
      Follow the instructions in the article, see also the reply under the next comment below.
      Then try a higher drive power, maybe 30 watts. You’ll see that the optimum load position will be higher (on the scale) with higher drive. Always keep the plate peaked, that’s the first thing when hitting the key. Watch the grid current, keep it under 135 or so.
      Once you are comfortable and certain of your procedure, find load for 55-60 watts drive. Increase the load just a bit over the point where max output was located. Chart the settings. That’s your final load number for that freq.
      Always work into a flat SWR, or your load setting, and meters, will be all wrong.
      73, –kv5r

  8. I have an al80b and have never been tuned properly because of the instructions are terrible.
    my question after reading so many articles is,

    Which is it, do I adj the plate for max then go clockwise with the load to where it dips slightly?
    Then people say to dip the plate.

    I am totally confused and will probably never understand. I think my tube has gone I only get 500w with 70w drive.

    • Howdy Ron,
      You must always peak the plate to max output. At peak output, the plate current will dip a bit. As stated in the article, you can peak the output or dip the plate current, same thing. I use peak the output because it’s a more obvious reading than plate current dip, which is very slight. Some hams will say dip the plate because they run an amp without a wattmeter.

      First, 70 watts is too much drive for that tube. Turn it down to 55 or so. Be sure to read your drive power into a dummy load (or tuner with SWR flat 1:1), with the amp in standby.

      Follow the instructions in the article to find the best Load position. You want to start with the Load too high and work it down, because if you start with it too low, you’ll arc the tube and blow a hole in the grid.

      Peak the Plate and note the output. Move the Load one mark down on the dial, then peak the plate again. Keep moving the Load 1 mark down, key up quickly and peak the plate. Peak power will come up and up. Then you’ll find a Load setting where peak starts to go down, after peaking Plate each time. Go back the other way 1 mark with the Load and peak the Plate again.

      The Load point you’re looking for is Peak Efficiency, ie, max output for min input. This is where you’re making the most RF and least heat.

      NEVER increase your drive power to compensate for a mis-tuned amp — your grid current will go up, heat will go up, something will burn up, probably the tube. Keep your grid under 140 and plate under 425 during brief testing. The tube’s published ratings are 125 and 400, and a little bit over that is ok for short key-downs during tuning with carrier. In SSB, they will be WAY below that because of low duty-cycle of the voice waveform.

      If your tube is good, you’ll find a Load setting (with peaked Plate) where 55 watts in will give you about 775 watts out. Grid will be about 130ma, plate will be about 380ma.

      On mine, on 80 meters the Load ends up at 1-1/4 (ie, 1 mark above “1”) with 55 watts drive. That is a MUCH lower Load setting than the manual states for 80 meters (3-3/4). Every amp and tube is a little different, so published settings are pretty meaningless.

      Remember to run it into a FLAT 1:1 SWR, or your plate and load settings will be different, and your wattmeter will be way off, and you have no idea where you are.

      Remember a “best” Load setting is only “good” for a particular drive level and frequency. If you increase the drive, or go way up the band, you need to determine a new Load setting.

      Remember the Plate must ALWAYS be peaked, or the tube will get orange hot real fast even at moderate power levels. The Plate control resonates the output tank circuit at a particular frequency. The Load control is like a variable transmission between your engine and wheels, allowing you to run the “engine” at peak efficiency for a given load condition.

      73, –KV5R

  9. Just curious if there is anything other than what you have covered in terms of set up for the 7100 that would apply to a 7300 ? As well, any other additional interfaces required for that radio?

    Thank you for the thorough, well-written article on this amp.

    • Please see a couple recent comments on the interface page.
      If I had a 7300 I’d loop 12V thru a current limiting resistor and and SSR input, to the SEND jack. You don’t need anything to reduce the current (the SEND jack can sink 500ma), but isolation is a good idea, in case there’s ever an arc-over on the amp’s T/R relay.
      As for settings, be sure to put in 30 ms transmit delay, somewhere in the settings menu.
      73, –kv5r

  10. I bought an AL80B last year. I find the instructions that came with it are somewhat difficult to follow. My Elmer set it up with a foot pedal to drive it and I am sure the instructions were written for an ALC connection. Could you please explain the ALC and how to hook it up?
    Your write-up is a breath of fresh air! Thank You!

    • The ALC is simply a feedback loop from the amp that limits the radio’s output power so the amp cannot be over-driven (if the ALC is set properly). You hook it up according to you radio’s manual. The radio will have a jack, or 2 of the wires in a multi-pin Accessory plug, for ALC input.
      You should also hook up amp keying from the radio and not use a foot-switch. Foot-switching an amp is a great way to burn up that big t/r relay in the amp, as you will inevitably press or release the switch while transmitting. Switching the relay under load will damage its contacts, sooner or later.
      See also: .
      73, –kv5r

  11. Thanks so much for this information. I have been a ham for a very very long time. I was always an appliance operator and not to much on the technical stuff. I operate mainly as a DXer and an award chaser. Your article explained in simple instruction with illustrations how to operate the AL-80B correctly for maximum performance.
    Again Thanks on a job well done.

  12. I just upgraded to an AL-80B (used) from a 811H and love the amp. I am, however, a bit perplexed about adjusting the ALC SET on the front of the amp (not the back ALC adjustment). Do you have a tune-up procedure for the ALC SET function?

    I did enjoyed your article and it made me wished I had spent the extra money for a new AL-80B so I could enjoy the new smell, etc.!

    • The ALC SET position of the multimeter switch simply runs some
      voltage to the meter to give you a reference reading that’s finer than just using the knob position.
      When tuning up, turn the ALC way up so it has no effect on the radio; set the radio’s RF power control at ~60-65 watts; tune up; then reduce the amp’s ALC until it just barely starts to reduce power. Thus, you will have a “maximum drive limit” protection, as a feedback signal from the amp to the radio.
      If you run the radio’s output at 100 watts, then use the amp’s ALC to limit it to ~60 watts drive power, the ALC action will be all from the amp, and none from the radio, which is fine, except if you accidentally crank the ALC up, you’ll overdrive the crap out of the amp, possibly blowing the grid. So I prefer to use both the radio and the amp’s ALC to hold it at 60 watts drive.
      In other words, both the radio’s RF power control, and the ALC from the amp do the same thing: bias the radio’s ALC circuit to limit peak output power. So, you can use one or the other, or both, which is the safest way.
      73, –kv5r

    • I thought about making a video, but just can’t do it. When tuning up I’m standing right in front of the amp, right where a camera would need to be to get useful video. So I’d either be reaching around the camera (on a tripod and too close), or between the camera and the amp. Maybe a hat-cam would work but I don’t have one!

  13. Thanks a million. Great stuff. The statement, “Tuning a high-power tube amp is no simple matter for newbies,” resonated with me (pun intended).
    Prior to receiving my AL-80B, I watched numerous YouTubes and read several articles online concerning proper tuning technique. Then, when I received mine and carefully moved step by step by the official user manual, I could not tune it properly. I finally gave up that evening before I did anything stupip.
    Fortunately, the next morning I happened on your article when looking for guidance. I had previously read the information posted by W8JI, the amplifier’s designer. Nevertheless, after reading your article and printing out the tuning instructions, I successfully tuned up the AL-80B for the very first time. Hallelujah! That was two days ago. Since then, I have been busting piles and really enjoying amateur radio at a new level.
    You might want to consider posting a PDF file of just the tuning directions for download. But in any event, it is a great resource that helped me out immensely.
    Thanks very much and 73.

    • Tuning an amp is actually quite easy once you get a “feel” for it. Trouble is, describing it always makes it sound more complicated than it actually is. Imagine if you tried to describe, in writing, every single step and precaution of simply driving to the store and back…
      Glad you found my attempt useful!
      73, –kv5r

  14. I found the Ameritron Manual a little confusing on certain points particularly setting the final grid current and the initial grid search. At any rate your straight forward instructions and pics are clean and easy to follow for a first time amplifier owner. I am still learning but your information answered many questions. Thanks and 76

    • Yes, I had the same experience with the manual.
      It would do well to say, never exceed 160ma grid current during tuning; and the normal operating condition is: about 60 watts carrier drive, 135 grid, 425 plate, 775 watts output. At least, that’s where mine is happy on 80 meters.
      It gets more confusing during initial load setting discovery, where you determine the best load setting at a little above normal operating drive power, to ensure the amp is slightly over-coupled, so that, at normal power, it never “clips” by trying to swing the plate to 0 volts.

  15. good information , lots of hams dont know how to properly tune a amp. Your photographs were spectacular. And very good instructions on assembly and setup. Thank you for your contribution to the ham community.
    de ke4amq

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