Overview Ameritrons legendary ALA kilowatt amplifier has been completely redesigned and extensively improved. It saves hundreds of watts wasted as heat. You get up to a full kilowatt PEP output from a whisper quiet desktop linear. Its a compact 8.
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All Rights Reserved. Introduction There comes a time in every hobby where we have to decide to either back out of it or get serious. I ran barefoot 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 year sunspot cycle, and most of the HF activity is on 75 meters — and 75 is a very noisy band, especially in the summer. I studied the situation for a few weeks, and finally settled on the Ameritron ALB amplifier.
Everybody that has one loves it. But with the M you still have to add a 75 amp power supply, which is several hundred dollars more, and then you have a watt amp that cost almost as much as the B. The H, called an watt amp, is really , has flimsy tubes that like to pop, and has no RF power meter. So in the end, I stand by what many others say, that the ALB is the best value per watt in new HF linear amplifiers. Since I run a multi-band ladder line-fed dipole, and my auto-tuner is rated at watts, I also purchased an MFJD, their largest antenna tuner.
Yes, there are better antenna tuners, but only at twice the price. The wait is over. Two big boxes—now the work begins… GigaParts shipped the tube in the big box with the D tuner, and it was double-boxed and well-padded in foam rubber. An implosion would ruin your day, so handle with extreme care. I unpacked it on the bed, and left it there until installed.
It also has active peak-reading meters, antenna switch, bifilar-wound current balun, and dummy load, which if purchased separately would cost as much as this tuner. The new tuner goes under the and , since the ALB 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. 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. 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. 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.
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! 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.
The B will draw about 12 amps at volts at full output. Switch on! No smoke, no pops, just a hair under volts, exactly what it should be. By the way, the forward and reflected meters are active peak-reading meters, so you see real PEP, not average, when running SSB voice. The filament works, too. So How Does it Work?
Please follow your manual, and do some research before tuning up for the first time. 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. Still not satisfied, I then discovered the writings of W8JI , who just happens to be the designer of Ameritron amps. 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! You can do it either way, since the B has meters for both. The Load control determines the coupling between the tube and the output. It is dependent on both frequency and power level. It cannot be accurately set at low power, but must be set at maximum drive, then left there as the drive power is reduced to the normal operating level, which is about watts PEP for the ALB.
Since the controls interact, the Plate must be peaked after every move of the Load. The most important indication when tuning up an amp is the grid current. An under-coupled amp will have high grid current, which will quickly in a few seconds destroy the tube.
The maximum continuous grid current rating for the G is milliamps, but for very brief max-power tune-ups, mA probably will not destroy it, but mA will. The manual says mA 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 watts, will run the grid at about ma, and the plate current at about ma.
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 ma, but then talking you only see maybe 80ma. I have found that, on mine, around mA grid, and mA plate, produces about watts.
Pushing it to 1kW pushes the grid into the danger zone, around mA grid and mA plate. Even at , the grid current is just too high for comfort! We see, then, that finding the Load setting, at maximum power, must be done in several very short tests, seconds on, seconds off. We then make a chart of settings and return to them for subsequent operations, at a 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. The Load is moved along little by little, and each time the Load is moved, the Plate must be re-peaked. After several short-duration max-power tests, an optimum setting will be found for the Load, which will be maximum output power, but with the grid current in the safe zone.
This is repeated at several frequencies across each band, and recorded in your chart. 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. 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 maximum power.
In my opinion. 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 output impedance of the tube changes with power.
For example, your Load might be best at 4 when driving the amp to watts, but at 3 when driving it to watts. 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. Do your Load discovery into a dummy load, and then always operate into a Ohm load antenna 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? 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.
Use the charted setting you determined at maximum power. Check the frequency and do not QRM.
Ameritron HF Power Amplifiers AL-80B
All Rights Reserved. Introduction There comes a time in every hobby where we have to decide to either back out of it or get serious. I ran barefoot 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 year sunspot cycle, and most of the HF activity is on 75 meters — and 75 is a very noisy band, especially in the summer.
Amplifier Weight: Quantity: Sold individually. Only this model has a two year warranty, excluding vacuum tube. When activated, they can more than double your average SSB power and produce up to 6 dB improvement in intelligibility. This maximizes your talk power without distortion and splatter. A convenient front panel control lets you adjust your output power level.
Ameritron AL-80B HF Power Amplifier