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Re: [Amps] SS Amps are expensive...why?

To: amps@contesting.com
Subject: Re: [Amps] SS Amps are expensive...why?
From: "Roger (K8RI)" <k8ri@rogerhalstead.com>
Date: Wed, 23 Jan 2019 19:05:43 -0500
List-post: <mailto:amps@contesting.com>
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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Roger (K8RI)


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