Because the H has 4 tubes and the non H has only 3. And the power supply is
smaller.
73
Jim W7RY
--------------------------------------------------
From: "W7MJM" <w7mjm@arrl.net>
Sent: Wednesday, February 09, 2011 12:27 PM
To: <amps@contesting.com>
Subject: Re: [Amps] AL-811 & 572's
> 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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