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[Amps] AL811H and Chinese 811As

To: Amplifier Reflector <>
Subject: [Amps] AL811H and Chinese 811As
From: Jay Sturtevant <>
Date: Thu, 7 Jan 2021 15:22:44 -0500
List-post: <>

I recently purchased a set of finals from Ameritron/MFJ for my AL811H, but
have not installed them yet because I have "heard" and read the newer 811A
tubes do not have the same specs as the ones the AL811H was originally
designd around.  My amp was new in 2008 and the tubes I'll be replacing are

I read that in 2011 the company did modify the original design. Now, I
believe, each of the grid resistors and  paralleled capacitors (RC) have
been removed from the circuit. The grids now go directly to ground. There
may have been other mods as well (??).

There are too many postings on the internet to draw a clear conclusion as
to whether or not I should make any modifications to my AL811H to
accommodate the new finals.  I was told by a tech at Ameritron, "no
modifications are necessary to accommodate new 811As, just check the 51 ohm
grid resistors". I like that!

I don't want to blow a new set! Thanks for your help!

Jay, K2ZT
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