> 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
> -----Original Message-----
> From: Scott Manthe [mailto:scott.manthe@gmail.com] On Behalf
> Of Scott Manthe
> Sent: Wednesday, April 09, 2008 10:08 PM
> To: Joe Subich, W4TV; Amps@contesting.com
> Subject: Re: [Amps] Replacing 811A with 572B
>
>
> 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.
>
> While the cost difference seems substantial, you'll probably
> never have
> to replace a 572B, imported or otherwise, when run in an AL-811H. RF
> Parts lists the Marshall 811A at $29.45 each and Chinese 572Bs at $39
> each, so the price difference at this point is substantial,
> but not so
> much so, if you consider the increased life expectancy.
>
> The size difference between the two tubes does not present a
> problem in
> the AL-811H amp.
>
> 73,
> Scott, N9AA
>
>
> Joe Subich, W4TV wrote:
> > Why waste the money ... four 572Bs are half again to twice the
> > price of four 811s. The 572B will not provide any more gain or
> > power output than the 811 unless you modify the power supply for
> > about 40% more voltage (2 KV vs. 1400 V).
> >
> > The 572B is taller and wider which might represent a problem
> > (moving the plate caps too close to the metal case or overly
> > restricting air flow between the tubes).
> >
> > If you are really concerned about reliability pick one of the
> > better 811 suppliers - perhaps Marshall (made in the USA) -
> > but I would not waste the money and effort on imported 572Bs.
> >
> > 73,
> >
> > ... Joe, W4TV
> >
> >
> >
> >>
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