> I am not quite convinced that the Ameritron amps are
> "tuned" to ham bands. From what I have seen of the solid
> state FET amps is that the input is broadband matched, and
> the output if filtered using simple low pass filters for
> each band. This is fairly evident in looking over the
> HL-2.5K schematics. My unfinished homebrew HL-2.5K will
> definately work out of band. Looking at the ALS500 and
> 600, it's likely this is the case there as well, and the
> amp could easly be used on the mars bands.
The cost of $1 per watt is unobtainable in a good quality
production amplifier. Remember it has to meet FCC
requirements, and that means a good filter. About the only
capacitor that will work is a multilayer HV chip cap, and
they are $5 each or more. The filter board alone at 1500
watts would cost a few hundred dollars just in parts, then
you have to add the PA modules and the power supply.
I know people think manufacturers make a good profit on ham
gear but in fact it is a very low margin market. People are
lucky to make 10-30% return on investment.
That aside, any of the solid state amps will transmit
anywhere.
The problem with tube amps is mainly the plate choke and
switch ratings, and the fact the amps MUST have 160 meters
or sales will be dead. The Q cannot generally be doubled
without problems with heating of the switch, and on low
bands the loading cap runs out of range. The tuned input is
also an issue. For good harmonic, efficiency, and IM
performance the input circuit needs to present a very low
impedance for harmonics at the cathode.
The plate choke is the real problem. To work at all on 160
the choke will always have an unwanted resonance on at least
a few upper HF frequencies. That puts holes in the coverage.
There are ways around the plate choke issue. In commercial
amps I've built, I wound the tank out of large copper
tubing. The HV feed runs through the tubing on a good Teflon
insulated wire, and then the choke is placed at a low Z
point near the loading cap. This totally eliminates the
choke problems, but it takes room. When the amp is four feet
wide and has 1/2 inch tubing in the tank it is easy, but not
in something that sits on a desk. Still that is a solution
for homebrew amps. Using that method and multistage input
and output networks using vacuum caps it is possible to do
1 - 35MHz with only eight switch positions and not have any
holes, but can you imagine trying to build a production amp
for $1500? The output tank alone would cost far more than
$1500 at 1500 watts.
A second solution is to switch the plate choke.
The end result is the only real solution for Hams (cheap)
wanting 1.8-30MHz coverage would be a solid state amp, and
they'd have to cough up at least 3-4K if they wanted
something with legal performance.
Anyone can build a one-off thing that gets by for his own
use, but it doesn't work when parts have to be bought new
and the FCC reviews the construction and performance.
73 Tom
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