3X572 AL811

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I designed the original Ameritron AL811 and AL811H. The Ameritron AL811 and AL811H are exactly the same in every way except cabinet dimensions, number of tubes, and the AL811 does not have neutralization.
The AL811 is supposed to have a 200-ohm 25-watt swamping resistor to replace the missing 811 tube. This is primarily to make drive levels the same, and prevent grossly over driving the three tube AL811. The swamping resistor also helps a bit on ten meters, where the 811 does not have the neutralization used in the 811H.
This amplifier is a refurbished newer AL811. We corrected all the poor solder joints, added a TOF module, added the 200 ohm resistor, did the arc and power supply upgrades, corrected some improper factory grounding, and added three 572B tubes. We also replaced the fan with a correct fan, MFJ for some reason is now using a fan with 1/3 the correct original airflow mass!
For the last few years all AL811s are shipped with a totally inadequate fan, and it is inadequate even for SSB use! If you have a Cooltron fan...change it!
Some claim 572B's do not increase power, and that is true in the sense of instantaneous peak power and even with very low duty cycle carrier power in the AL811H. This claim is NOT true at all in the AL811!!! The AL811 benefits much more with 572 tubes because it is tube anode dissipation limited in all modes, and 572's increase dissipation by almost 250%. The AL811 with 572's actually exceeds the AL811H in all mode duty cycle when all units have the correct fan.
The weakest link in Ameritron AL811 amps, other than fan and assembly errors, is tube dissipation. Once amplifiers are brought up to standards the weakest link is tube dissipation.

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Опубликовано:

24 мар 2022

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Комментарии : 21

@hobbiehobbs 2 года назад

You’ve said that you don’t like making videos. But your darn good at it and at explaining the inner workings of these amps. Please keep making more videos Tom 💪

@CoryDRicci 2 года назад

Tom you are the absolute master in these fields of study -- genuis would be an understatement! I wish i could be an apprentice of yours, even at the ripe age of 40 I'd rather be in field i am passionate about and never am sick of amd learn from the best there is to learn from! Thanks for doing these videos, theyre awesome i hope you do more in the future. Your website is my absolute go-to for cold hard facts on every subject you cover as its presented in a way to make the reader understand why the answer is what it is versus just the answer itself but not having an understanding of the principles that dictate it. Appreciate it Tom! 73 Cory K9CDR

@JohnStruemph 2 года назад

Sweet! Had no idea the 811 could do that with mods. You are going to get 2 of them from me to convert/ upgrade

@AB1Vampire 2 года назад

Over 900 with only 1700 on plate is great day for any 3 572b"s

@Jerrythenerdful 2 года назад

Even 811 tubes, which do not even have oxide on the filament like 572's do, can do well into 1000 range on peak emission tests at 1500-1700V. You don't want to run them at peak saturated emission, but that is an excellent test to root out poorly made or worn-out tubes. It is much better that looking at them at lower emission levels.

@G3PWP Год назад

Hi Tom amny thanks for this video it has been very very useful please make more useful videos

@procerpat9223 Год назад

how are you getting 150W out of a barefoot IC-746?

@richb.4374 6 месяцев назад

This is the same guy who strongly advises not to turn up radios for more output yet he's done that with his own rig.

@NFarmer 2 года назад

Tom, just picked up an 811. Can I just replace the 811 tubes that are in it with 3 572Bs? And will that provide more than 600 watts? Do I need to do any other upgrades ? I could not see a brand of fan on the back of my amp to see if it had a Cooltron fan and I didn’t see where it did.

@eduardogarciamontesdeoca5935 Год назад

I’ve seen some AL-811 with 572B swaps and grids directly connected to ground… does it make a good RF ground to the grids?

@chuckstonex1632 Год назад

I have an AL811 SN 19537 with the ten meter mod that will not key up. I bought this used a year ago and this is the first time I have hooked it up, so I don't know if it was working when I bought or if the 10-meter mod had something to do with it. Thanks KA5PAL

@Gabaab 2 месяца назад

can the 811H (4 tubes) run with 3 572b with no issues?

@PaulReedy 2 года назад

When you say proper fan, what do you mean? I have an early 90's 811 with a 33cfm fan. I just put a set of 572b's in it, and can get 700w (rtty mode when tuning up) when I max out the grid current. So along that lines, in your video, you have the plate current at about 750ma, peaked on the meter. I haven't gone back on the tube specs, but you're not concerned with going into the red on Plate current?

@Jerrythenerdful 2 года назад

Fan CFM free-air ratings are all over the place from the actual measured flow in the amplifier. I don't know what fan you have, but any Ameritron 811 amplifier with the Cooltron fan (which seems to go back at least four years) will have woefully inadequate airflow, about 1/3 of the air necessary for 811 use. Even though the manufacturer claims near 25-35 CFM (depending on the data source) the Cooltron fans measure 8 CFM inside the amplifier. This is a major problem because temperature rise inside the amp will be 3 times what it should be at a given heat dissipation. I'm not in the least concerned about anode current. The life threat to 811 tubes is short term average anode dissipation. Anode temperature is primarily the killer of tubes. The 572's have a much more robust anode, easily making a three-hole 811 with 572's far more reliable than an 811H with four 811 tubes.

@PaulReedy 2 года назад

@@Jerrythenerdful Thanks Tom. The fan that's in my 811 is an MG Electronics SF11580A, the sticker says 33CFM

@Jerrythenerdful 2 года назад

@@PaulReedy 33CFM is the "supposed" free air CFM. That rating doesn't mean much. That is actually a Sunon 31cfm fan. It flows about 15 CFM in the 811 amp, which is marginally okay for SSB and CW with 811 tubes. The data sheet for your fan is here: www.alliedelec.com/m/d/e7fa8e9dca7dd90ce204f7d91c175fed.pdf

@weslewis8748 Год назад

What brand/model fan do you recommend

@cliftonhead9665 7 месяцев назад

Help with any amp, pickup an amertran al-811h amp. When it arrived all 4 tubes are out of there sockets, and one has a broken top cap. Everything looks okay BUT. The man said he would replace all 4 tubes. Would you return the amp or install the new tubes.

@Jerrythenerdful 7 месяцев назад

It sounds like the packing was no good or the handling was very rough. If the tubes became unsocketed and moved around inside the amplifier and broke, chances are very good other things are damaged. I would not even attempt a repair by installing new tubes. My advice would be to return it. You might get into a mess if you start repairing an amplifier you just bought.

@timbacchus 2 года назад

Well that is more PEP than the 600 of the 811 tubes

@smithderf Год назад

So I see you used a pulser. There's not a lot of pulser information on the web other than explanations of how it works and why we use it. Every article I have read either uses the CW input or has the pulser wired to the micrphone for SSB pulsing. No one has every used a simple two dollar app to create the same pulse audio and just use the microphone element as the conduit. Maybe others can chime in but I see no disadvantage to using this two dollar method instead of 50 plus dollars for a hardware pulser.