The other aspect of running constantly at 100W is the temperature of the finals
and drivers: that would concern me much more. The MTBF drops like a stone at
constant high temperature; everything else in the box will also be at raised
temperature. I don't know how good the Pro is at shifting heat, but it's a
general principle when calculating MTBF to MIL STD 217. Your linear is built
to cope with much higher than 100W average power without much affecting its
reliability ratings.
David
G3UNA
---- Roger <sub1@rogerhalstead.com> wrote:
>
>
> Mike wrote:
> > I seem to remember reading someplace that the final Transistors used in most
> > 100 watt rigs are do not give a very clean output at 10 watts or so, 25
> > watts and up the output is clean, now this normally would not make any
> > difference if you were just running 10 watts QRP because no one can hear
> > you. But, when you amplify that 10 watts with an external amplifier then
> > who knows how it may spatter across the band. Anyway just a thought, if you
> > have a Scope it might be worth taking a look at the signal.
> >
> >
> It's been quite a while since I was involved at that level, but I think
> that would be dependent on the particular transistor(s) and the circuit.
> The curves for the 2SC5125 transistor listed as the two finals in the
> Icom 756 Pro III look to be fairly linear even in the low end. However
> the impedance running 10 watts versus 100 watts out it's designed for
> should change considerably with a fixed network. I'd think that would
> create quite a mismatch. Those are rather impressive transistors rated
> at 80 watts out each into an SWR as high as 8:1 at 175 MHz. So running
> the Pro III at the full 100 watts gives a large safety factor. That
> being the case, with the Pro series I'd not give a second though to
> running the thing at full power.
>
> OTOH I'm surprised to see transistors rated for such a high frequency
> used as low as 1.8 MHz. In "the old days" VHF transistors didn't do
> well at the low end of the HF spectrum. Of course back then we also put
> a string of resistors and caps across a string of diodes, something no
> longer needed.
>
> 73
>
> Roger (K8RI)
> > Mike
> >
> > -----Original Message-----
> > From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com] On
> > Behalf Of Ken Bills
> >
> >
> > While RTTY contesting this weekend, I wondered, since my amp still was
> > warmed up, if it made sense to run the Alpha at 100 watts output, versus
> > pushing the exciter at it's 100 watt limit. It only required about 9-10
> > watts output, to deliver the 100 watt contest limit.
> >
> >
> >
> > I am sure this doesn't help my carbon footprint, but it may save the finals
> > in the Icom ProIII.
> >
> >
> >
> > Any thoughts?
> >
> >
> >
> >
> >
> >
> >
> > _______________________________________________
> > Amps mailing list
> > Amps@contesting.com
> > http://lists.contesting.com/mailman/listinfo/amps
> > No virus found in this incoming message.
> > Checked by AVG - www.avg.com
> > Version: 8.0.237 / Virus Database: 270.11.5/1977 - Release Date: 03/01/09
> > 07:04:00
> >
> >
> > _______________________________________________
> > Amps mailing list
> > Amps@contesting.com
> > http://lists.contesting.com/mailman/listinfo/amps
> >
> >
> _______________________________________________
> Amps mailing list
> Amps@contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|