Joe,
The AL-811h is what it is, bad design or not. I'm not here to debate
that. I live in this world, not the best of all possible worlds, as
Voltaire might say. Given that, the 572Bs, even the generic Chinese
tubes, which is the only version currently available, are a good choice
in the AL-811H. They are certainly more reliable in this particular
application than the 811A.
Hopefully, you've got a good supply of N.O.S. American made tubes. No
one else does however, so whatever your complaints are regarding the
Chinese tubes, it doesn't really matter, because they're the only ones
available.
Your points are well taken regarding the Chinese tubes and the higher
voltage the AL-811H puts on the 811A, but we're not talking that. The
question was whether the 572B was a good replacement in this particular
application. Given these parameters, the answer is yes.
73,
Scott, N9AA
Joe Subich, W4TV wrote:
>> The AL-811H runs about 1600-1800 volts HV, not 1400, which is
>> why it's not a bad idea to run the 572Bs in that amp.
>>
>
> If the AL-811A plate voltage runs that high it is exceeding the
> "Maximum Plate Voltage" rating for the 811A tube and is a bad
> design. The RCA data sheet calls for 1500 V maximum in ICAS
> service and I would not want to push an 811A harder than that.
>
> Unless the newer tubes are designed for higher plate voltages
> the 572B would be a safer choice. However, I don't see any
> really reliable 572B. I would certainly would not use a generic
> $39 Chinese 572B.
>
> 73,
>
> ... Joe, W4TV
>
>
>
>
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