Carl,
I didn't see anything on the Ameritron site that would answer my particular
question, but perhaps I didn't dig deeply enough or think it through
thoroughly.
In any case, Colin, W7FM, and Bill, WA4LAV, seem to have explained it to me.
I know the 811A to 572B swap has been discussed quite a bit, but the
question as to why Tom, W8JI, recommends only 3 572B's in the AL-811H (with
the fourth hole empty) had continued to puzzle me.
I assumed one would want to drive the AL-811H, after retubing, to it's full
800 watts, so how could 3 572B's still deliver that output if they can't do
it in the AL-811? The additional current draw of 572B's as compared to
811A's, and the need to reduce the AL-811H output to 600 watts hadn't
occurred to me.
So, as I now understand it, 3 572B's, with plate voltage in the neighborhood
of 1500 volts, will deliver the same 600 watts as 3 811A's. So, assuming the
power supplies are the same in the AL-811 and AL-811H, retubing an AL-811
gives you no increase or reduction in maximum PEP output (600 watts), just
longer tube life, tolerance of overdriving, and tolerance of extended
tuning, while retubing the AL-811H means sacrificing 200 watts of potential
output (reduced to 600 from 800) in exchange for longer tube life, greater
tolerance of overdriving, and greater tolerance of extended tuning.
Do I have it right? If so, retubing the 600 watt PEP output AL-811 with
572B's makes sense, but retubing the AL-811H with 572B's is not necessarily
beneficial, assuming you want maximum 800 watt PEP output from the
four-holer.
73 and thanks to all who responded,
Martin, W7MJM
----- Original Message -----
From: "Carl" <km1h@jeremy.mv.com>
To: "W7MJM" <w7mjm@arrl.net>; <amps@contesting.com>
Sent: Wednesday, February 09, 2011 1:21 PM
Subject: Re: [Amps] AL-811 & 572's
> Go to the Ameritron site and find out.
>
> Carl
> KM1H
>
>
> ----- Original Message -----
> From: "W7MJM" <w7mjm@arrl.net>
> To: <amps@contesting.com>
> Sent: Wednesday, February 09, 2011 3:27 PM
> 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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