Yes indeed; it appears to be the same power supply transformer in both the
AL-811 and the AL-811H.
The conclusion I'm coming to is, IF you can run 800 watts PEP output from an
AL-811H using 3 572B's, with the fourth tube socket empty, then you should be
able to run 800 watts PEP output from an AL-811 with a trio of 572B's in its 3
Of course, there may be other limiting factors in the AL-811, as compared to
the AL-811H, of which I'm not aware.
In any case, I'll continue to run my AL-811 at no more than 600 watts PEP
output, just to be on the safe side. It's not worth pushing the envelope, so to
speak, for that additional decibel!
----- Original Message -----
From: The Zwiener
Sent: Thursday, February 10, 2011 2:15 PM
Subject: Re: [Amps] AL-811 & 572's
The power transformers are the same in the 811 an 811H
I was curious too and looked at the manuals. Talk to MIke at Ameritron to
Have fun and be safe!
> Thanks Bob and all those who responded to my queries. I now have a better
> understanding of the AL-811 vs. AL811H amplifier capabilities when
> with three 572B tubes.
> To be sure, I'm not looking to squeeze out more wattage than these amps
> reliably, and linearly, deliver, nor am I considering a bigger amp. I'm
> happy with 600 watts and have no desire at this time for more RF power. I
> was just curious about W8JI's suggestion some time back about running
> three 572B tubes in the AL-811H, presumably at 800 watts PEP output, as
> opposed to running a trio of 572B tubes in the AL-811 at 600 watts PEP
>> From the various comments, I now understand that the power supply in the
> AL-811H is what allows three 572B tubes (or four 811A tubes) to generate
> watts PEP output, whereas the power supply in the AL-811 is what limits
> output to 600 watts regardless of whether you're running a trio of
> 572B's or
> When you come right down to it, it's the transformer that delivers the
> power, though I suppose you could take it further up the line to the
> company's generating plant. The tubes are, well, "valves" as they say on
> other side of the pond.
> In any case, my AL-811 continues to serve me well, with good reports and
> issues three or four years after swapping out the 811A's for 572B's.
> Incidentally, when I removed the 811A's, which I had been using for maybe
> three years at the time I swapped them out, they showed the tell-tale
> plate welts, indicating that I had overheated them; sufficient reason
> for me
> to go to 572B's for their additional anode heat dissipation capabilities.
> ----- Original Message -----
> From: "Robert Kirkland" <firstname.lastname@example.org>
> To: <email@example.com>
> Sent: Wednesday, February 09, 2011 7:17 PM
> Subject: [Amps] AL-811 & 572's
>> The amount of plate current a triode tube will draw depends on it's
>> voltage. The 572B is usually operated from 2200 to 2700 volts. The 811A
>> usually operates around 1500 to 1800 volts, be careful, some brands of
>> foreign 811A's are not rated for as much plate current as is necessary.
>> The full load voltage on the AL-811 is 1500 and the plate current is 550
>> ma. That's about 600 Watts output, with the 572B's there is not enough
>> plate voltage and plate current to produce much more. The only reason to
>> install 572B's is, used at these low ratings the tubes will last forever
>> and you won't over heat them on a long tune up. You could increase the
>> voltage by messing around with the power transformer primary input
>> settings but then the filament voltage would be way out of limits and
>> surely the transformer would over heat. If I had an AL-811 Linear and I
>> wanted more power I'd trade it in on another amp, or try to improve the
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