With only 1500 or so volts on the plates the 572Bs have low gain.
You may not have enough drive to go beyond 600 watts. Unless you operate a
higher
plate voltage you may not go beyond 600 watts anyway.
If you go by the specs. even for three tubes in parallel, with 2500 V
plate voltage
and 150 watts drive you will get 900 watts.
73
Bill wa4lav
At 03:27 PM 2/9/2011 -0500, you wrote:
>Is there anyone on the list who can answer my question as to why three
>572B's in the three-hole AL-811 should only put out 600 watts whereas W8JI
>has suggested (if memory serves), that when retubing the four-hole AL-811H
>with 572B's, only three are needed and the fourth hole can be left empty?
>
>If an AL-811H retubed in this manner puts out 800 watts PEP, why not the
>AL-811? Is the power supply different?
>
>Waiting to be enlightened, but without any arcing. :-)
>
>73,
>Martin
>W7MJM
>
>
>----- Original Message -----
>From: "W7MJM" <w7mjm@arrl.net>
>To: "mitch cox" <ww4cox@embarqmail.com>
>Cc: <w8ji@contesting.com>; <w8ji@w8ji.com>
>Sent: Wednesday, February 09, 2011 10:36 AM
>Subject: Re: [Amps] AL-811 & 572's
>
>
> > Very interesting, Mitch. I think I'll just stick with the 600 watts rated
> > output (my old Healthkit HM-2140 PEP meter shows 500 and my new MFJ-868
> > shows 800); obviously I need to calibrate the meters, but the drive is
> > about 70 watts so I'm probably putting out about 600 to 650 watts.
> >
> > With the three 572Bs in place, I don't have to worry as much about tune-up
> > mistakes cooking the anodes, and the tubes seem to take up to about 100
> > watts of drive while staying under 165 mA on the grid current meter and
> > there are no reports of bad audio or splatter.
> >
> > The reason I wondered whether the trio of 572B's in the AL-811 would put
> > out 800 watts is because Tom Rauch, W8JI, who designed the amp, suggests,
> > when retubing an AL-811H with 572B's, that it's only necessary to install
> > three 572B's and leave the fourth hole empty. So I figure, if three tubes
> > in the AL-811H produce 800 watts of output, why not the same result in the
> > AL-811? Is the power supply different?
> >
> > I'll cc Tom and see if he has any thoughts about this.
> >
> > 73,
> > Martin
> > W7MJM
> > ----- Original Message -----
> > From: "mitch cox" <ww4cox@embarqmail.com>
> > To: "W7MJM" <w7mjm@arrl.net>
> > Sent: Wednesday, February 09, 2011 5:18 AM
> > Subject: Re: [Amps] AL-811 & 572's
> >
> >
> >> If you wire the buck boost on the transformer to the highest voltage
> >> setting, 2200 VDC, 800 watts is a breeze but....you are also raising the
> >> filament voltage to a dangerous level. I tested one of these transformers
> >> in a home brew 2 months ago along with 3 Svetlana 572B tubes. At the
> >> highest voltage setting I got 900 watts out with 75 watts of drive. I
> >> also wondered about how stout this little transformer was so with good
> >> cooling, unlike the factory amp, and a separate filament transformer, I
> >> locked this home brew down at 900 watts CW for 1 hour, 20 minutes. No
> >> problems were encountered with either the tubes or the tranformer. The
> >> transformer was warm after the test but not hot and the amp will still
> >> produce 900 watts so nothing was harmed. At 85 watts of drive this amp
> >> will do a full KW with the same tubes as used in the test.
> >> ----- Original Message -----
> >> From: "W7MJM" <w7mjm@arrl.net>
> >> To: amps@contesting.com
> >> Sent: Tuesday, February 8, 2011 11:57:18 PM
> >> Subject: Re: [Amps] AL-811 & 572's
> >>
> >> "Thanks for the input guys. I'm aware of the limitations of the power
> >> supply
> >> on the AL-811. I was looking for performance information about the 572B
> >> tube
> >> itself."
> >>
> >> Isn't the power supply in the 3-tube AL-811 identical to the power supply
> >> in
> >> the 4-tube AL-811H? If so, shouldn't you be able to run the 3-tube AL-811
> >> at
> >> 800 watts PEP output when it's been retubed with 572B's?
> >>
> >> Anyone care to comment on this?
> >>
> >> 73,
> >> Martin
> >> _______________________________________________
> >> Amps mailing list
> >> Amps@contesting.com
> >> http://lists.contesting.com/mailman/listinfo/amps
> >>
> >
>
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