Ameritron AL-811 - Elmers Forum at eHam.net

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eHam.net Forum : Elmers : Ameritron AL-811

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Ameritron AL-811	Reply
by K1FPV on April 5, 2005	Mail this to a friend!
I know of several folks who purchased the AL-811 with 3 811A finals and replaced them with 572B's. They run cooler and if you drive them a little harder, you will get between 700 and 800 watts out. Has anyone ever tried to use just 2 of these tubes in the amp?

RE: Ameritron AL-811	Reply
by K7JBQ on April 5, 2005	Mail this to a friend!
Why on earth would you want to use two tubes in a circuit designed for 3? The tubes aren't that expensive. 73, Bill

RE: Ameritron AL-811	Reply
by WB2WIK on April 5, 2005	Mail this to a friend!
>by K1FPV on April 5, 2005 Mail this to a friend! I know of several folks who purchased the AL-811 with 3 811A finals and replaced them with 572B's. They run cooler and if you drive them a little harder, you will get between 700 and 800 watts out.< That's not a great idea. The reason the AL-811 and 811H use 811As and not 572Bs was to cut cost not only on the tubes, but also on the power supply components by operating at the lower 811A plate voltage. If you run 572Bs (2.4kV tubes) at 811A voltage (1.5kV), you can't just drive them harder and produce more output without increasing distortion products, and probably eventually making the power supply fail. A clean 600W signal from the original tubes (or replacements using 572Bs) is a much better signal on the air than the distorted one created by 572Bs being driven to excessive grid current. Using two tubes instead of three creates a plate tuning network mismatch and risks possibly damaging the filaments from excessive voltage, since the filament winding of the transformer won't be fully loaded and therefore will produce higher potential. I'd recommend using the amp as it was designed to be used; but replacing the 811As with 572Bs does work and the beefier tubes should last longer in the same service. WB2WIK/6

RE: Ameritron AL-811	Reply
by N6AJR on April 5, 2005	Mail this to a friend!
you really don't get any more out of the 572's than the 811's.. the problem is that you have the same plate voltage, 1800 if I remember right, the 572 amps run them at 2200 or so. so with out tearing the amp apart and rebuilding with a new transformer, higher value components etc, you are just wasting money. you run the tubes at 1800 volts at 700 mills max so nom matter which tube it goes through the same power goes out the back. And the amp is designed for 811's the 811 are about $50 for a set of 3 from ameritron, the 572's are about $50 each from ameritron. the 811 amp is about $550 new from ameritron so its is a good value for the $. If I had a set of 811's fail and had a set of 572's on hand and no 811's I would run them for convience sake, but would not get any better performance pout of them. BTW I probably have 10 811's and 10 572's in my extra tubes box, so I would really just put back in the 811's. this is a myth propagated by some. and I have never worn out a set of 811's in either of my 811 amps or the 811h amp. sold them all and have also had sweep tube amps , several clipperton L's ( a good 572 amp) , some amp supply stuff, and ameritron als500, and others, I am currently running a IC 2kl on the 756 and a alpha 76 A on the 746. so save your money and use 811's in the 811 amp.

RE: Ameritron AL-811	Reply
by W0SDI on April 22, 2005	Mail this to a friend!
I also have thought about replacing the 811 with the 572B. The reason is I have to replace the 811's every 6 months or so and I don't even use the amp that much. The 811's don't last. They short out all the time. The last time I only used the Ameritron with about 300 watts output but that didn't help. I called Ameritron to see if I was incorrectly tuning the amp. I guess the 811's are not built very good anymore. Any suggestions on why they short out all the time????

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