I agree with you Manfred, With a couple of exceptions.
SS amps (including those in many high priced 100 and 200 W rigs) have
historically had poor IMD.
To build a SS amp with a CLEAN output requires an amp capable of running
almost twice the desired output. So an amp for a clean 1500W legal limit
should be capable of close to 3 KW out. Adding the REQUIRED low pass
filters capable of 3KW may cost as much or more than the rest of the amp.
As you well know, but many don't, 3 KW low pass filters are not tiny.
This amp would pretty much require the latest state of the art
transistors. (Expensive and unlikely to be found at swaps) Even then we
are probably looking at two pallets with 2 transistors each. IOW, 4
transistors, each capable of 1.5 KW (3KW out at 50% = 6KW input) = some
big dollars plus combiners to combine the signals from the two pallets.
The big limitation here is eliminating 3 KW worth of heat from 4
physically small transistors. This means a LOT of work, skill, and
knowledge in heat transfer. The mating surfaces on the heat spreader and
the transistors need to be flat! Really flat! Lapping surfaces close to
being close to optically flat takes skill! Sometimes hours of effort
and a great deal of mechanical aptitude.
Then there is the exotic heat transfer compound selection and the
ability to apply it properly. This is where "the bigger the gob the
better the job" will produce poor results. The compound's job is to fill
tiny (microscopic) voids in the mating surfaces. Applied correctly in
the correct amount the transistors will feel kike it's welded to the
heat spreader
Many of these capabilities/requirements are outside the realm of the
sharpest people in electronics and old timers. I know how, but no
longer have the physical abilities.
SS amp control? It can be built in or done by computer. Neglecting the
software, we still need to get the required signals, in the proper form
to the computer which may require substantial hardware in the SS amp
adding still more cost.
Then there is the software (programs) which by themselves can be
RELATIVELY simple BUT getting them to all work together may get
complicated.
(CS, more than just programming, is my field)
Now where I disagree on a couple of points. With today's licensing
structure (needed to build our numbers to justify our use of very
expensive frequencies) bringing in many younger and less educated people
with little money or interest in electronics into ham radio, lowering
the average age of hams. Yes there are those few who are expanding the
envelope, bringing with them things like dynamic predistortion. STILL
the knowledge level (and abilities) of the average new ham just like the
average new college graduates, is abysmal. (I taught at the university
while working toward a masters in CS and was dismayed at the abysmal
intelligence in those classes) I can't ignore the inability of many old
timers to adapt to the new technology either. At my age, I'm now an
appliance operator. Those large displays are often necessary to display
many important functions in advanced SS amps.
IOW: That famous phrase, "It's complicated", but it all adds up, and
does lead to some very expensive amps and rigs.
Some rigs are expensive and over priced, but some bring new technology
with extremely clean signals. There's IMD not seen since the Collins
S-Line and at over -70 db a new high on the bar for Ham gear. Yes the
100 and 200 W versions are expensive, but there are some relatively
inexpensive lower power versions out there. Leading edge gear will
likely remain expensive.
73, Roger (K8RI)
On 1/22/2019 12:09 PM, Manfred Mornhinweg wrote:
Lee,
Why are solid state amps so expensive?? Even the kits are lots of
dollars.? ?What makes them so?
Here is my view on this matter:
The high price of SS amps is caused by a number of factors. I will
list them, in random order:
Capacitors: SS amps are broadband, and so they require lowpass
filters, ideally one per band, although one can skimp somewhat and
manage two close-by bands with one filter. So an amp that covers all
ham bands from 160 to 6m will need between an absolute minimum of 6,
and an optimal number of 11 filters. If two-section elliptic filters
are used, at least 5 capacitors are required per filter, and possibly
more if some value has to be implemented by paralleling capacitors.
Each of the capacitors needs to handle roughly 1000V and 10A, to be
safe and reliable, or at least 500V and 5A, but then it has almost no
headroom for slightly elevated SWR. Such capacitors tend to cost
between 10 and 20 dollars each! So we are talking of $300 to over
$1000 just in capacitors for the lowpass filters! Add to this a few
capacitors of comparable specifications that are needed in the
amplifier proper. And if the amp includes an antenna tuner, as many or
most do, add another considerable number of them in the tuner! So a
premium amp might contain $1500 just in RF capacitors.
Homebrewers and very small companies might get away cheaper, by using
junkbox specials, Russian military surplus, or even homebrewing the
capacitors, but companies that want to produce under well controlled
conditions can hardly do that.
Inefficiency: Essentially all ham HF amplifiers you will find are
class AB designs, which tend to have an efficiency of only around 50%
at envelope peaks, dropping from there at lower parts of the envelope.
Due to still unresolved problems coupling the drains of push-pull
transistors, class AB broadband SS amplifiers are significantly less
efficient than tuned, narrowband tube-type class AB amplifiers. This
is a problem of low impedance broadband push-pull operation versus
high impedance, single-ended, tuned operation, rather than a
fundamental problem of solid state versus tubes. The low efficiency
requires the use of enough transistors to safely handle the heat,
together with huge heatsinks, copper heat spreaders, powerful fans,
maybe even watercooling. It also requires larger power supplies. These
power supplies tend to be much better than tube amp power supplies,
delivering well regulated DC voltage over a wide range of line
voltages, and usually also include power factor correction circuitry,
which makes them easier on the power lines. All this costs money.
Engineering: HF communications is a niche market, ham radio is just a
part of this niche market, and the proportion of hams buying new SS
amps is tiny. So the sales numbers of ham SS amps are very low, which
means that all engineering costs need to be absorbed by relatively few
units. So each amplifier sold carries a considerable amount of
engineering costs.
Manual labor: For the same reason (small amounts sold), companies
making amplifiers or kits cannot automatize the whole production. A
lot of manual labor is used. And these days anyone who works in
electronics rightly wants to get paid a decent hourly rate. This
reflects on the price tag. Manufacture of cabinets, front panels, etc,
is also more expensive for small runs.
Rich customers: Most hams nowadays are old people, or at least adults,
not school kids. The typical ham these days is retired, has time for
playing, has worked for many years, and has earned enough money. In
his old age he wants to play radio, putting his money to good use. If
he gets interested in a piece of ham gear that costs $5000, or even
$10,000, he might just pay that price, for the joy of having that nice
piece of engineering in his shack! After all nobody can take his
savings into the grave. Use them or lose them. This has created a
small but open-handed customer base, which some companies are serving
with overpriced, luxury ham gear. Icom for example offers a $12,000 HF
transceiver. It has good specs, sure, but the practical advantage it
gives over a transceiver costing a small fraction of that is tiny, if
there is one at all. Yaesu follows with a $9000 one, and Kenwood, more
modest, "only" charges $6500 for their flagship. All these radios are
made to give rich hams a lot of knobs to play with, adorned with
gold-colored stripes and the like, while a $2000 radio already can
feature all the performance modern technology allows. And something
similar is happening with amps. Several companies are striving to
offer "no compromise" SS amps, offering 1500W CCS, fully automatic
operation, the largest possible color LCD screen (as if that was
important...), one company even has been caught advertising the large
number of lines of code in their amp's control software... In short,
the companies are trying to offer the best amps they can, with cost
being no issue, to serve this small but attractive market of well-off
hams willing to spend a lot of money for a piece of equipment they
fancy. The interest in serving price-conscious (AKA cheapskate) hams
with legal-limit, simple, straighforward, budget amps is far lower,
probably because the size of that market isn't enough to let
manufacturers earn a decent amount with small-margin products aimed at
that market.
So let's home-brew! That's the essence of ham radio, anyway.
Manfred
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