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Re: [Amps] AL-811 & 572's

To: "The Zwiener" <>, "aMPS" <>
Subject: Re: [Amps] AL-811 & 572's
From: "W7MJM" <>
Reply-to: W7MJM <>
Date: Thu, 10 Feb 2011 19:22:24 -0800
List-post: <">>

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 
tube sockets.  

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 
  To: W7MJM 
  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 
  > retubed
  > with three 572B tubes.
  > To be sure, I'm not looking to squeeze out more wattage than these amps 
  > can
  > 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 
  > only
  > 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
  > output.
  >> 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 
  > 800
  > watts PEP output, whereas the power supply in the AL-811 is what limits 
  > the
  > output to 600 watts regardless of whether you're running a trio of 
  > 572B's or
  > 811A's.
  > 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 
  > power
  > company's generating plant. The tubes are, well, "valves" as they say on 
  > the
  > other side of the pond.
  > In any case, my AL-811 continues to serve me well, with good reports and 
  > no
  > 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 
  > silver
  > plate welts, indicating that I had overheated them; sufficient reason 
  > for me
  > to go to 572B's for their additional anode heat dissipation capabilities.
  > 73,
  > Martin
  > W7MJM
  > ----- Original Message -----
  > From: "Robert Kirkland" <>
  > To: <>
  > Sent: Wednesday, February 09, 2011 7:17 PM
  > Subject: [Amps] AL-811 & 572's
  >> Martin,
  >> The amount of plate current a triode tube will draw depends on it's 
  >> plate
  >> 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
  >> antenna.
  >> Bob,
  >> w5pvr
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