Ameritron AL-811 problems

[Captain Kilowatt]

I have a ham buddy that runs an AL-811H off the 120 volt line and has no problems other than a very slight flicker of the ceiling light on voice peaks.He runs about 700 watts pep out and has done so for several years on the original tubes.Admittedly 240 volts would be better but it should run half decently on a 120 line.

 

[paws264]

I have a Ameritron AL-811 that has been converted to use 572B tubes. When I got it it would only do 100 watts so I replaced the tubes, let it sit on stand by for a day and then it would do 800 watts for a while. But after a little while it would start dropping off on power so I let it sit on stand by for several days and everytime I checked it it would be doing less power and now it only does about 80 watts.

I have a ham buddy that runs an AL-811H off the 120 volt line and has no problems other than a very slight flicker of the ceiling light on voice peaks.He runs about 700 watts pep out and has done so for several years on the original tubes.Admittedly 240 volts would be better but it should run half decently on a 120 line.

IMO there has got to be something wrong with this "Conversion" to the RF sensed antenna switching and the 572B's.

Turn it off and let that thing cool down, take the screws out and the covers off, trace the center-tap lead of the filament circuit. Find out what's going on there.

Did you own this equipment before the modifications or did you buy it in this condition?

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[KD7UGY]

Sorry I haven't updated you guys in a while. I put a new set of 572B's in the amp and now it works pretty good, I can get 400 watts out of it with about 20 watts input and I haven't tried driving it any harder than that. The conversion to 572B's and to RF switching was done several years before I got the amp so I'm not sure on how it was done. But the guy that owned it before me told me it worked great for many years, but when he tried driving it a little harder than normal the output dropped off so he put it in the closet for a couple of years then decided to sell it.

 

[paws264]

Update, where are you at now output wise; those new tubes have cooked for a week now.


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[paws264]

I have a Ameritron AL-811 that has been converted to use 572B tubes. When I got it it would only do 100 watts so I replaced the tubes, let it sit on stand by for a day and then it would do 800 watts for a while. But after a little while it would start dropping off on power so I let it sit on stand by for several days and everytime I checked it it would be doing less power and now it only does about 80 watts. So does it make sense that it could go through tubes just sitting on stand by? And why would it do that? Could it be that the power supply voltage is too high? I think the voltage sits around 1800 volts according to the meter, but I'd have to check to make sure.

So, I guess this thing spontaneously healed itself?


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[KD7UGY]

Here's the latest update on this amp. I have used it very little for the past couple of months since it's summer time and time to work outside but I have been using it a little on 40 and 80 meters and with about 20 watts in it puts out around 400. I can't say it healed itself because I put new tubes in it and the old tubes were definitely "soft". I don't know for sure what caused the old tubes to go "soft" but I'm assuming it was a drop in filament temperature caused by voltage drop. I'm planning to run a 220 circuit to my radio room sometime soon and when I do that I'll drive those tubes a little harder and see if they'll last. Thanks again for all the help and input, that's what I love about this forum.

 

[DuckKilla]

You didnt say how old this amp is.Might need new filter caps.With that low plate as has been stated those 572Bs should last forever.I dont think its low line voltage from the what you describe but its possible.I had a homebrew amp running 1 811A driving three 811As and it was 110 and I ran it on 50 year old wimpy wiring for awhile and had no problems and I even ran it with 572Bs but with low plate the only thing your really gaining is very long tube life.Were the tubes you installed new?
I think your B+ is dropping.Bad diodes,filter caps or a wiring problem would be my list of suspects.Could even be a problem with the tank circuit but not likely.
Just my two cents.Good luck.

 

[Mikey1966]

Uh, you're not running this from a 120-Volt 15-Amp outlet, are you?

With adequate filament voltage on that tube, a 572B should last more or less forever in that box. It's like running a box meant for the 572B on "low" side all the time.

If you're running it on 120 Volts, and the outlet circuit isn't stout enough, you'll see the color of the filaments inside, dim noticeably with full drive.

This would indicate that the line voltage was falling under load, causing the 6.3 Volts on the filaments to fall, as well. This dimming of the yellow-white filament color indicates that the filament temperature is falling.

Running that filament at too low a temperature can and will cause the tube to go "soft", and appear to be worn out and weak.

If this is in fact the root of the trouble, you won't see those filaments dim when you key it now. If you remember seeing that happen when they were 'fresh', that would be a clue.

And if you're running it from a stout 240-Volt circuit, this is probably not the cause.

73

You can run it on 120 volts with no issue. Ameritron will tell you the same. I have the same amp & tubes, runs fine on 120 vac.

 

[Amperex]

With 1800 volts and 500mA plate current those 572B's should show no color on the plates whatsoever under keydown conditions.In standby mode they should last a lifetime.As Ed said,check the bias.If it is too high the tubes will draw too much current but should still not be damaged.I would be suspicious of something in the power supply causing a drop in plate voltage but it must be awfully low to cause only 60-80 watts output.How many watts are you driving it with and is it being tuned and loaded properly?

Finding reliable 811A or 572B new tubes is impossible now. NOS Cetron is your only choice.