> OTOH the 572s are much more rugged and tolerant.
The only difference is plate dissipation. Operated at 1250 volts
on the plate and not overdriven, 4 x 811A have more than enough
plate dissipation for service at 800W PEP output.
> They should run until they die of old age.
The most likely failure is of the cathode - not the plate. Since
the cathodes are the same, there will be no difference in life
between the two tubes unless someone tries to put a brick on the
key.
> Of course you can't get that cherry glow as quickly out of
> the 572s as with the 811s<:-))
Sure you can ... if the 572B is operated at or above its maximum
ratings like some 811As.
73,
... Joe, W4TV
> -----Original Message-----
> From: amps-bounces@contesting.com
> [mailto:amps-bounces@contesting.com] On Behalf Of Roger (K8RI)
> Sent: Wednesday, April 09, 2008 10:36 PM
> To: Amps@contesting.com
> Subject: Re: [Amps] Replacing 811A with 572B
>
>
> Joe Subich, W4TV wrote:
> > Why waste the money ... four 572Bs are half again to twice the
> >
>
> Waste? When compared to most tubes in the 1KW to legal limit
> either the
> 811 or 572s are down right inexpensive. OTOH the 572s are much more
> rugged and tolerant. They should run until they die of old age. So,
> when I look at it that way the 572s are less expensive over
> time than
> the 811s. Of course you can't get that cherry glow as quickly out of
> the 572s as with the 811s<:-))
>
> To me it's a good choice (IF they'll fit)
>
> 73
>
> Roger (K8RI)
> > 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
> >
> >
> >
> >
> >> -----Original Message-----
> >> From: amps-bounces@contesting.com
> >> [mailto:amps-bounces@contesting.com] On Behalf Of Bert Almemo
> >> Sent: Wednesday, April 09, 2008 7:37 PM
> >> To: amps@contesting.com
> >> Subject: [Amps] Replacing 811A with 572B
> >>
> >>
> >> Hi guys,
> >>
> >> I have a friend who wants to replace 4x811A with 4x572B in an
> >> Ameritron amp. I don't think it's a good idea but he insists
> >> a lot of hams do it. What do you think?
> >>
> >> 73 Bert, VE3OBU
> >>
> >>
> >
> > _______________________________________________
> > Amps mailing list
> > Amps@contesting.com
> > http://lists.contesting.com/mailman/listinfo/amps
> >
> >
>
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