[Amps] AL-811 & 572's

[Carl]

A well tweaked Clipperton L will do 1200W at 100W drive. The manual 
specifies maximum drive at 150W and it will do 1500W out but the bandswitch 
is already stressed so I dont recommend it.

At 2400V the 572B gain is around 12dB, it varies a little tube to tube and 
manufacturer. A 2 tube amp such as the SB-200 can be driven to max with as 
little as 75W....even as a 6M monobander. At 1500-1600V figure on 10dB PEP 
gain as the PS doesnt sag as much as with a steady carrier with the filter 
caps providing stored energy.

Some try to drive a 30L1 with 572's at 150W and get more out but the 
transformer is already marginal.

Carl
KM1H




----- Original Message ----- 
From: "Fuqua, Bill L" <wlfuqu00 at uky.edu>
To: "W7MJM" <w7mjm at arrl.net>; <nz4o at tampabay.rr.com>; "aMPS" 
<amps at contesting.com>
Sent: Tuesday, February 15, 2011 1:13 AM
Subject: Re: [Amps] AL-811 & 572's


>   If you run 572Bs at say 1600 volts on the plates rather than 2400 as in 
> the spec I would expect about 20% decrease in output and gain.
> Even going by the specs 3 572Bs would produce 900 watts output with 2400 
> volts plate voltage but the drive power would be around 150W.
> I'd expect if you ran 3 with 1600 volts with 900 W output there would be 
> considerable distortion.
>   I am just trying to get the claims to agree with the published 
> specifications. Somewhere I have seen some specs for 572B's run at lower 
> voltages
> but can't find the source just now.
>   The nice thing about 572Bs is that they are inexpensive. A rather good 
> value value in terms of W/$.
> Some day I want to build 5 4CX250Bs in GG ( control grid connected to 
> cathode) driven by one in GG for a low distortion
> low drive amplifier. Should get a power gain of 20 to 25.
>    I have a 6 tube distributed power amplifier to convert.  Just need 
> spare time.
> Say, who is going to dayton this year? I plan to bring some stuff. I can't 
> bring much heavy stuff.  I have some plasma
> generator amplfiers and other interesting stuff. Need to clear out the 
> garage a bit if possible. Maybe should have
> my own hamfest fleamarket. Hi Hi
>   Email direct if you are going and looking for something in particular.
>
>
> 73
> Bill wa4lav
>
> ________________________________________
> From: amps-bounces at contesting.com [amps-bounces at contesting.com] On Behalf 
> Of W7MJM [w7mjm at arrl.net]
> Sent: Sunday, February 13, 2011 1:49 PM
> To: nz4o at tampabay.rr.com; aMPS
> 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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