I do not think the power supply of the AL-811H can handle four 572's.
This is why when you change from 811's you don't see that big of a power
output jump in the AL-811H.
The power supply is at the edge of its design.
It can hardly four 811's.
Now, the Al-811 can do better with the 572's because with only three tubes
you have a little extra to drive those tubes from that power supply.
In fact the AL-811 does not suffer from those sudden pops and unrest as does
the AL-811H.
Before going to the AL-811H I would recommend dropping three 572's in an
AL-811.
You will get the same output as with the AL-811H.
I would still suggest not to push it. Keep it at about 1.7KV .
If you want more output than 600 watts CW you need another amp.
With any equipment, when you go over the design tolerance you are asking for
trouble and funny things start to happen.
All it takes is a reactive load and bam, kaboom, and golly gee Batman.
MFJ went to the edge with the AL-811H and some operators are driving it over
the cliff.
Don't blame MFJ.
Dan/N4VET
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