[Elecraft] Time for the KPA-1500

[Guy Olinger K2AV]

Well, after a long study on the matter, I bought an Alpha 8410, and might
get another one.  Some interesting counterpoint on the amp discussion.

In 1958, the brand spanking new Collins 30S1 uses a single 4CX1000A
tetrode, which was already "commercially popular".

In 2012, a brand spanking new Alpha 8410 uses a PAIR of 4CX1000A tetrodes.

Hmmm,  how many other 1958 vintage transmitting tubes still in heavy use
that you know of.   Maybe a reason for that?

In 2012, 4CX1000A's are still manufactured in large quantities for medical
and manufacturing uses.  There is a lot of manufacturing equipment  using
4CX1000A's that may still be operating 50 years from now.  These do basic
fundamental tasks, such as "sputtering", that do not change. Some of that
equipment may have been operating 50 years ago.  These will NOT be replaced
unless there is a cost-effective reason.  The people who make 4CX1000A's
will continue to use the same equipment to make them until the cows come
home, or until the demand dries up.  As long as the manufacturers who use
the paid-for equipment that uses the tubes can get replacement tubes, they
will have no incentive to replace the equipment.  That's what is called a
symbiotic relationship.

In ham amplifiers, 4CX1000A's are operated to full output in class AB1 (no
grid current), because they require negative bias on the control grid, and
bias plus max positive-going signal voltage is still always negative.  That
means that very large swings, huge swings, in output Z can be tolerated
without destroying grids.  With my 8410 I can drive full power into an SWR
up to 3:1.  This allows me to cover 1.8 to 1.92 at full power without
faulting on SWR.   Since it faults on reflected power, not SWR per se, I
can drop back power and operate 700 watts out at a 7:1 SWR at 1999 kHz.

I don't need to retune every 25 kHz, just need to have two switched antenna
settings across 160 and maybe 3, depending on the antenna, across 80/75.

Are transistors really ready for 1500 watts brick-on-key with oodles of
dissipation headroom.  What is the price/point analysis of an absolute
brick-on-key 1500 W transistor solution that will suck up 3:1 SWR without
folding or faulting?  So far that's still pretty expensive PLUS a
brick-on-key 1500 W tuner to do what the 8410 does.

Not tooting the 8410, it's expensive, but analyzing it helps to get
comparisons out into clarity.  By the time we are at a transistorized
brick-on-key 1500 watts into nearly anything, we have crossed more than a
few dotted lines that today still require paradigm shifts.

73, Guy.


On Mon, Feb 20, 2012 at 10:12 PM, Gary K9GS <garyk9gs at wi.rr.com> wrote:

> Same here...I recently bought a used Alpha but the advantages of a K3
> integrated legal-limit amp would interest me too.
>
> On 2/20/2012 4:23 PM, J&J Kulp wrote:
> > I too want a KPA-1500, and it does NOT have to be solid state, nor does
> it need to have a tuner, just interface and change bands like the KPA-500
> does.....That would get my checkbook out in a hurry.......
> >
> > jim, K3SW
> >
> > On Feb 20, 2012, at 12:36 PM, Peter Chamalian wrote:
> >
> >> Don't get me wrong.  I love the KPA-500 for its nearly instant on  and
> >> instant band change.  But in an event such as this past weekend ARRL CW
> >> (ditto CQWW and other major contests), 500 watts may put you in the high
> >> power category but it definitely does not put you in the same league as
> the
> >> guys running the legal limit.
> >>
> >> With the advances in solid state devices, I truly hope the folks at
> Elecraft
> >> have a KPA-1500 on the drawing board or at least a KPA-1000 with a tuner
> >> (just like the Yaesu Quadra amp).
> >>
> >> I'm willing to bet you will sell a bunch of them, too!
> >>
> >> Pete, W1RM
>