> The question was whether the 572B was a good replacement in this
> particular application. Given these parameters, the answer is yes.
I consider the question to be one of replacing 811A with 572B in
general. Except for the unique case where the high voltage is
above the 811's ratings, the answer is still "not worthwhile."
The filament power is identical so the peak current capability
is the same ... the amplification factors are generally the same
so the 572B will not provide more power output unless the power
supply is modified for increased voltage.
73,
... Joe, W4TV
> -----Original Message-----
> From: Scott Manthe [mailto:scott.manthe@gmail.com] On Behalf
> Of Scott Manthe
> Sent: Wednesday, April 09, 2008 11:30 PM
> To: Joe Subich, W4TV; Amps@contesting.com
> Subject: Re: [Amps] Replacing 811A with 572B
>
>
> 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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