[Top] [All Lists]

Re: [Amps] AL-811 & 572's

To: W7MJM <>
Subject: Re: [Amps] AL-811 & 572's
From: "Joe Subich, W4TV" <>
Date: Wed, 09 Feb 2011 22:47:17 -0500
List-post: <">>
I suggest you download the AL-811 and AL-811H from the Ameritron web
site then compare schematics/parts lists.  That is what any other
person would need to do to answer your question.

If the schematics and parts are identical, you have your answer.
If they are different, you have a different answer.  The power
supply specifications are different between the two amplifiers -
700 mA for the AL-811H vs. 550 mA for the AL-811.  That's a hint
right there.

In addition, since the 572B is an 811A with a heavier anode and the
811 is only clean to about 200W PEP per tube, I would not expect
three 572Bs to be clean at 800 W with only 1500V on the plates.
Now, if one chose to raise the AL-811 plate voltage to 2250V (and
the rest of the components could handle the increased voltage), I
suspect one could easily see 1000W PEP from a 3 x 572B AL-811.

The AL-811 is restricted as much by the limited plate current
capability of the 811A tube at 1500V as it is by the plate
dissipation (cooling) of the tubes.  Substituting a beefier anode
does nothing for the plate current capability.


    ... Joe, W4TV

On 2/9/2011 3:27 PM, W7MJM 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
> ----- Original Message -----
> From: "W7MJM"<>
> To: "mitch cox"<>
> Cc:<>;<>
> 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"<>
>> To: "W7MJM"<>
>> 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 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"<>
>>> To:
>>> 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 mailing list
Amps mailing list

<Prev in Thread] Current Thread [Next in Thread>