Thanks Bill. That makes sense to me. But given those numbers, why would Tom
(W8JI) suggest, when retubing a 4-hole AL-811H to only go with 3 572B's,
leaving the fourth hole empty? Unless I misunderstood a previous post of
his. Any ideas?
----- Original Message -----
From: "Bill Fuqua" <email@example.com>
To: "W7MJM" <firstname.lastname@example.org>; "aMPS" <email@example.com>
Sent: Wednesday, February 09, 2011 1:59 PM
Subject: Re: [Amps] AL-811 & 572's
> 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
> 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.
> 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. :-)
>>----- Original Message -----
>>From: "W7MJM" <firstname.lastname@example.org>
>>To: "mitch cox" <email@example.com>
>>Cc: <firstname.lastname@example.org>; <email@example.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" <firstname.lastname@example.org>
>> > To: "W7MJM" <email@example.com>
>> > 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" <firstname.lastname@example.org>
>> >> To: email@example.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
>> >> _______________________________________________
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>> >> Amps@contesting.com
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