[Elecraft] KPA500

[Guy Olinger K2AV]

There ya go, the drive-it-until-it-smokes instinct.

That WORKS on CW .....  as long as it doesn't fault, or burn something,
because class C and CW get along well together.  BUT SSB cannot exceed the
** LINEAR ** range of the amplifier without splatter, which means
drive-it-until-it-smokes always generates splatter.  ANY amplifier can
generate CW power well beyond the linear range, 1) if the power supply will
supply it, 2) if the device does not burn up because of inability to
dissipate all the heat (and remember that solid state devices can have
runaway failures where they lose control of current before the current
carrying elements burn), and 3) if the amp does not have a fault system to
prevent the previous.

I can tune up my 3-1000Z monster to 2500 watts, too, (power supply is 5 kV,
2 amps CCS move-it-with-a-hand-truck monster) but if I do, it's gone WAY,
WAY, WAY off linear and spreads SSB up and down 10.  The huge range overkill
for a 1500 watt legal limit is to have the 1500 watt signal WELL down into
the linear range, it's not to run 2500 watts.  The double overkill 2 amp CCS
is to make sure that contesting does not burn it up, make it wheeze, or ever
come anywhere near close.  And the original owner may have been running more
than one amp with it.

I would have been quite happy enough with 1 amp CCS, but the total overkill
came with it when I bought it.

The KPA500 comes with internal over-range, that you can't get at because of
the fault system.  Elecraft is very well aware of ham radio's queer
self-destructive predilections and trying for maximum smoke (what a telling
Freudian clue in that idiom!).  AND also well aware that SSB does not
tolerate that.  They have their technical reputation to mind, and also know
that the outcome of "maximum smoke" usually gets shamelessly blamed on the
manufacturer.

In high school days we used to do drive-it-until-it-smokes with WWII surplus
ARC-5 transmitters, and could get 500 watts out of a pair of 1625's (two
twelve volt filament 807's in series to run off military 24 volt battery
systems).  We had a near inexhaustible supply of FREE 1625's and enjoyed
watching the tube envelopes and anodes melt holes in them.  Kind of like
fireworks without the explosion.

But the 1625's were free.  KPA500 and innards not exactly free...

Melting down 1625's WAS fun, but when it comes down to trying to hear
someone in an SSB contest, one could wish that every amp had the shutdowns
so people could NOT drive their amps into non-linearity and put all those
unnecessarily broad signals on the band.  Thank you Elecraft for putting
some linear range in the amp that people can't get at.

73, Guy.

On Tue, Sep 6, 2011 at 4:31 AM, Jon K Hellan <hellan at acm.org> wrote:

> On 09/05/2011 11:34 PM, Lyle Johnson wrote:
> > Yes, 500 watts PEP regardless of mode.  This is thus 500W RTTY/FM/CW
> > (key down :-) etc.
>
> Excellent, but then why limit it to 500 W in low duty cycle modes?
> Shouldn't it be capable of more? Are the intermod issues?
>
> Jon
>
>