Plate dissapation is a power limit for the piece of metal making up the
plate...Put DC on the Tube (no RF), make it heat up and measure the power
versus temp curves and decide what the limit should be. 4000V and 1 Amp
means 4000W going in to the tube plate.
Now lets consider the RF case. Put the same 4000 V and 1 Amp (average), but
apply RF and get power out. In class A, at 50% efficiency, power from the
power supply is still 4000W, but 2000W goes out the coax to the load. By
conservation of energy, the plate is now dissapating only 2000W.
In Class C with 75% efficiency, the same 4000V/1A power becomes 3000W output
and 1000W dissapation.
Plate dissapation is a tube oriented power limit, it's only indirectly
related to RF performance. Overall RF performance is determined by many
limits. Power (temperatures really), Voltage, Current, etc.
Transistors have the same characteristics. Manufacturer's rated dissapation
is a function of the package thermal resistance...the real limit is junction
temperature.
Most of the time, the real design limits for an amplifier are not the
thermal performance.
jeff, wa1hco
----- Original Message -----
From: "mark" <mark@sandlabs.com>
To: "Michael J. Tubby B.Sc. (Hons) G8TIC" <mike.tubby@thorcom.co.uk>;
<amps@contesting.com>; "John T. M. Lyles" <jtml@lanl.gov>
Sent: Wednesday, November 13, 2002 12:34 PM
Subject: Re: [Amps] Re: 8877 dissp
> I am lost ... Call me slow but I think we are going in circles here ...
> The Plate deals with two virtual "loads", a RF load and a Caloric Load.
> It realy does not matter where the loads DISSIPATE (ie being used) as long
> it originates in the
> same place ... the PLATE. If you can accept this, than the plate
> has TWO DISSIPATIONS ... an RF one that is delivered to the LOAD
> and a CALORIC one DISSIPATED into the ENVIRONMENT.
>
> I make a clear distinktion between DISSIPATION and DELIVERY.
> DISSIPATION, in generat has a conotation of wastefullness ... lost in
space
> if you will :)
> But I think all this is semantics. I am starting to understand now and
I'll
> deal with
> it my way :)
>
> Thanks to ALL.
> MArk
>
>
> .
> ----- Original Message -----
> From: "Michael J. Tubby B.Sc. (Hons) G8TIC" <mike.tubby@thorcom.co.uk>
> To: "mark" <mark@sandlabs.com>; <amps@contesting.com>; "John T. M. Lyles"
> <jtml@lanl.gov>
> Sent: Wednesday, November 13, 2002 11:49 AM
> Subject: Re: [Amps] Re: 8877 dissp
>
>
> > > Right!. However, I feel that the term PLATE DISSIPATION is somewhat
> > > missleading as
> > > it refers only to the caloric content of the entire work. As we all
> know,
> > > the Plate is used
> > > to deliver the RF energy also, which is not accounted in the term!
> > > I guess a more descriptive wording will be PLATE WASTED CALORIC
> > DISSIPATION
> > > :)
> >
> >
> > Not so. Plate Dissipation is quite correct since the rest of the power
> > goes into Antenna/Load Dissipation, thus:
> >
> > Pin = Plate Dissipation + Load Dissipation
> >
> > (assuming we ignore other trivial things like any power used to generate
> > xrays,
> > circulating currents in the walls of the enclosure, light, ionisation,
and
> > even sound).
> >
> > Mike G8TIC
> >
> >
> > _______________________________________________
> > Amps mailing list
> > Amps@contesting.com
> > http://lists.contesting.com/mailman/listinfo/amps
>
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