Oops. That quote was from NZ40, not NZ4Q. Got to clean my eyeglasses! Sorry
for getting your call wrong, Thomas. -MM
----- Original Message -----
From: "W7MJM" <w7mjm@arrl.net>
To: <nz4o@tampabay.rr.com>; "aMPS" <amps@contesting.com>
Sent: Sunday, February 13, 2011 10:49 AM
Subject: Re: [Amps] AL-811 & 572's
> "Martin I own an AL-811 with three 572B's and get 800 watts out PEP easily
> on SSB but run it at 400 watts PEP. I own an AL-811H with four 572B's and
> get 900 watts out PEP easily on SSB but run it at 600..." -NZ4Q
>
> Thanks for the info, Thomas. That makes sense to me. If three 572Bs in an
> AL-811H (fourth hole empty) can be safely, reliably and linearly driven to
> 800 watts PEP output in SSB service, then three 572B's in the 3-hole
> AL-811 should also be cabable of safe, reliable and linear operation when
> driven to 800 watts PEP output in SSB service.
>
> The power supplies of the two units seem to be identical, so the AL-811
> does not appear to be any more constrained in that department than the
> AL-811H.
>
> The neutralization argument would appear to be irrelevant as well, since
> 3-572B's in parallel, like three 811A's, are not quite at the point where
> neutralization is required, assuming I'm correctly interpreting Tom
> Rauch's explanation elsewhere in this forum as to why the 4-tube AL-811H
> (when actually running 4 tubes) requires neutralization whereas the 3-tube
> AL-811 does not.
>
> In any case, it's often a good idea to run an amp conservatively. Since I
> use a bit of RF speech compression (at most 5db), I figure my SSB duty
> cycle is slightly higher than unprocessed SSB, so I back off on the drive
> a bit and don't run my AL-811, with 3 572B tubes installed, to the
> absolute limit of its capabilities. Though the tubes might be able to take
> it in stride, other components in the amp would likely be right at their
> limit.
>
> I understand the AL-811H may have additional refinements over the AL-811
> (aside from neutralization). So even if the AL-811, retubed with 572B's,
> can be driven to 800 watts output, there may well be reasons other than
> maximum power output to buy an AL-811H, as opposed to an AL-811 plus 3
> 572B tubes. (The main reason I went for the 3-tube AL-811, even before I
> began to consider the implications of a 572B substitution, was that a good
> one came up on eBay at a very nice price from a very reliable seller. I
> didn't really care whether it was limited to 600 watts as opposed to 800
> watts, since the difference between those power outputs is less than 2
> decibels.)
>
> I am of course still interested in hearing what W8JI has to say, should he
> care to comment on this discussion. As the designer of the AL-811 series,
> Tom Rauch probably knows this amplifier better than anyone.
>
> Once again, thanks to everyone who contributed their thoughts, opinions
> and analyses. You've all been helpful.
>
> 73 and see you on the air,
> Martin
> W7MJM
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