Is it time for amplifier mfgrs to step back and "rethink"

Discussion in 'Amateur Radio Amplifiers' started by KM5FL, Sep 6, 2011.

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  1. K7JEM

    K7JEM Ham Member QRZ Page

    From what I got from the OP, he is not suggesting that individual hams design and build the amps, but rather that some manufacturer design and build the amps, or provide a kit. Hams typically do not have the resources to adequately design and test a totally new amp (some do).

    I think that if someone with the ability could design this, that it could be manufactured and meet all the parameters of the OP, except it would be SS and not have a tube. The LPF and switching would be relatively easy, as it is pretty much like any other design from the past 20+ years. The tricky part might be the broadband transformer on the output side, but even that might be pretty straightforward. As shown, a 50 volt PS can be purchased for under $200 that would easily run a 500-600 watt amp. Cooling could be done by conventional heat speader/heatsink with forced air or liquid cooling, it would have to dissipate about 200 watts when transmitting, which is not extreme for most methods.

    Lighning has been mentioned, but I don't think that these LDMOS would be any worse in that aspect than the transistors being used in virtually every ham transceiver that has been built in 20 years. We don't seem to have a terrible problem now with that.

    At $180, the LDMOS for 600 watts is almost exactly the same price as a new 3-500Z. Of course, the tube will put out a little more power, but maybe a dB or two. The expense of the part and the LPF's is mainly offset by not having to have several expensive HV tuning caps and fixed value caps that the tube amp needs. The already built 50v supply is likely to cost less than the parts to build a HV supply, when you factor in the new costs of transformers, capacitors, etc.

  2. WB3BEL

    WB3BEL Ham Member QRZ Page

    I think maybe we are saying the same thing. The parts for 500W tube vs 500W solid state are about the same. Maybe if you use cheap tubes like 811s its cheaper but one could probably find some cheap transistors if they want to use 2-4 of them...You make a HV power supply for the same cost <$100 as a similar VA rated switcher for DC at this power level. Obviously the switching power supply is lighter and maybe works over a wider input voltage and frequency range automatically so it has some advantage even if cost is not the driving factor.

    To me similar costs is not an Enabler to get to lower cost. Maybe some day the economy of scale of some newer semiconductors used will make them significantly lower cost than tubes. Or perhaps the cost or supply of tubes will diminish. Who knows?

    I am not pro SolidState vs Tube. My main point is that I can see why no manufacturer is jumping up and down to make a new design at this $1K price point. I am not saying its impossible. But I think my estimate is pretty close to right when you factor in everything that is not obvious in the oversimplification bucket I called labor (Facilities, Utilities, Cost of money, Management, Yield, Warranty, Legal, Accounting, Advertising, Amortization of Development, etc.). As I said you could erode your margins if you choose. I agree that eventually you might be trending down, but planning it from the start might mean eating a lot of peanut butter and jelly and making your supply chain less likely to promote your inventory.

    I think that looking at the current solutions is informative. My opinion is that the Ameritron AL80B is pretty close to this benchmark. A solid workhorse product that costs perhaps 30-50% above the bogey.
    The ALS600 is maybe a close solid state solution. Although my opinion is that the AL80B is considerably better.

    Then take a look at other options...The newly announced Elecraft KPA500 seems to be pretty close to the spec point. As a kit it costs ~$2K.

    So maybe someone will manufacture the $1K amp because they enjoy the hobby and don't see it as a business opportunity. Maybe they will do it because they want the fame and glory of accomplishment in the eyes of their fellow amateurs. But more likely to succeed they will go where labor costs a fraction and the materials are also cheaper. Which maybe goes to show that the cost metric is not the only important one...
  3. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    I've been following most of the comments and must say tube amps do have some advantages for many of us.

    The SS amps are pretty noisy because they require so much forced air cooling of the heatsinks. A way around that would be with liquid coolants, even water, but I don't really see anyone doing that at amateur power levels as commercial offerings. Every high powered tube amp I have (several) is quieter than the THP amps, or the ALS-1200, or the Quadra, or the PW-1, etc. If you haven't had one on your bench while operating it's hard to describe how noisy they are.

    Using way larger heat sinks with copper spreaders would reduce the air flow requirement but make the amps "bigger."

    Operating in places where it's hot and there's no A/C is another restriction on SS amps. While we enjoy moderate climates here and most have air conditioning, a lot of places don't. I have fairly wealthy relatives in the Philippines where it's 100F all the time and none of them have central air conditioning. We have to either derate systems or add a lot of "boost" cooling to racks of servers and storage systems when we ship to many parts of the world where the standard ambient in the computer room is 40 degrees C (can be higher). SS amps won't survive long in such environments without derating. Tube amps generally will (except for maybe filter capacitors); tubes are meant to get hot anyway and at 40C they run at the same seal temperatures as at 25C ambient.

    In my experience you can operate through a lightning storm using a tube amp and the likelihood of damage to the amp seems to be about zero. However, operating with local lightning activity using a SS amp -- I've seen several fail from this. Yes, we often operate right through lightning storms -- especially if it's a contest and we're in it.

    The critical PA to load matching is another issue, of course. An SS amp used without a tuner may never cover much of the band on 160m, and probably not on 80m either, with most conventional antennas. A tube amp with a conventional pi-net or pi-L usually can. The THP and Ameritron amps do not have internal automatic tuners. The Yaesu and Icom units do, and they'll handle maybe a 3:1 mismatch before they shut down.

    Pros and cons.

    I still like tooobs.
  4. KM1H

    KM1H Ham Member QRZ Page

    When SS can provide IMD in the -40's at glass tube prices then I might get interested. Meanwhile the 12V versions barely make -20's and the higher voltage arent much better until you get into 50V FET's.

    The TS-950SD uses a pair of MRF-150's for 150W out and IMD is excellent.

    Then you have a company peddling a 4 "pill" to mainly ex CBers at 600W and you just have to scratch your head.

  5. K0BG

    K0BG Platinum Subscriber Platinum Subscriber QRZ Page

    Well, the Icom 2KL uses a copper heat pipe assembly. It does have some sort of liquid inside. However, when the cooling fans come on, you would think a tornado just hit! The cooling fans in the power supply make a bit of noise too.

    My mobile amp is an SG500, and it does have the fan kit. They make a lot of noise, and in fact they can be heard inside the cab of my Ridgeline, even though the amp is in the trunk.
  6. W4AFB

    W4AFB Guest

    Exactly! This is my view also.
  7. AF6LJ

    AF6LJ Ham Member QRZ Page

    This has been an interesting thread;
    I'm in the camp that believes solid state HF amateur linear amplifiers are not quite ready for prime time. When you look at the Freescale parts they are derated heavily to keep IMD down to the mid thirties.... As Steve pointed out the current crop of SS amps are fragile when it comes to ESD from nearby sources such as lightning. Water cooling is great but without extraordinary measures the best you can hope for is several degrees above room temp...

    There is new technology on the horizon which might be a game changer.
    Every so often you see articles on carbon based transistors, they have been playing with this tech for nearly forty years now and some progress has been made. I wouldn't expect to see the tech hit the mainstream or even specialized applications for a few years however the prospect of high voltage, high temperature and very fast switching times make these devices very attractive IF they ever come to market.
    But for now without the tightly controlled environment modern solid state multi-kilowatt transmitters operate in the solid state parts are too fragile for amateur use in my opinion.

    The old saying about switching supplies applies here.
    You are just one microsecond away from disaster.

    What is really needed is a US company making the popular tubes to high quality standards however with job killing environmental regulations and states hostile toward manufacturing this isn't going to happen.
  8. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    I'm afraid part of the problem with vacuum tube manufacturing is most of the experts who really knew how to do it are dead, and those left will be dead sometime pretty soon.

    It would probably be hard to manufacture a good buggy whip today.
  9. WB3BEL

    WB3BEL Ham Member QRZ Page

    I disagree with your position about the readiness of Solid State Amplifiers for Amateur use. My point is more along the line that they are not drastically cheaper than tubes today.

    Your first point about IMD is somewhat valid. But you do know that most HF transceivers do not meet the 30 dB IMD don't you ? Sure there are a small handful of top of the line units that do. But the vast majority of hams are using rigs that are in the mid twenty dB range. Many of these are IMD/PEP spec not like Freescale's standard engineering IMD per tone. If you want good IMD performance you can always implement pre-distortion or feedforward or feedback technologies for solid state at the cost of additional complexity. A benefit is improved efficiency. You could get 50 dBc running class B at 60% efficiency if you wanted to. I think that 30 dBc/tone is fine for most amateur situations.

    Lightning can be an issue, but this is manageable with good engineering practice. I think some of solid state PA lightning failures are induced powerline related. Sure some are from the antenna interface but there are quite a few ham SSPA that are using un-regulated linear power supply that may be susceptible to transients on the power line interface.

    Water cooling is not needed. It could be quieter. And maybe a good solution at 100% duty cycle legal limit. But at 500W output there are plenty of other solutions that are adequate.

    Steve's WB2WIK point about the desirability of an integrated tuner is perhaps a compelling factor. The complexity and cost are about the same as tube based autotune amps that some operators like because they are easy to remote control or can be used by people who don't have the skills to adjust the controls. Obviously an outboard tuner is an option and some people prefer them as they can provide some pre-selector function for the receiver as well.

    I understand why some people prefer tube amps...No problem with that...But I do think that solid state is an option and also has some positive points. There are folks using Freescale and NXP LDMOS devices at 2m EME to make solid KW RF output running for hours 1min on 1min off duty cycle. Using switching power supply these SSPA are great for EME DXpeditions because they are lightweight.

    So in summary, I think that SSPA are rugged and reliable enough now for amateur service. I think we will be seeing more of them in the future.
  10. AF6LJ

    AF6LJ Ham Member QRZ Page

    An amplifier shouldn't add to total distortion, If you were to be listening to an audio source that say has three percent THD you wouldn't be willing to accept piling another one percent THD on tip of that in your audio amplifier. Good design works to keep distortion products below that of the source signal. I don't find that train of thought acceptable in my mind, I wouldn't knowingly put an amplifier that is as dirty or worse behind my radio.

    You touched on something that I want to address.
    One of the recurring themes in this thread is one around the thought that linear amplifiers should be plug and play, an appliance if you will.... I disagree strongly, if someone is going to run a linear amplifier they should know enough about how that amplifier operates to be able to tune it and operate it in a manner that is clean and stable. This whole idea of everything should be idiot proof smacks of another service which is welll...........
    I won't go there.

    In terms of VHF amplifiers I couldn't agree more, I couched my statements in terms of HF amplifiers where operating conditions are not so forgiving and the bands are no so crowded.

    Antenna, the percentage of bandwidth covered, the chance of mistrusting static charges on antennas and other factors I believe make sold state amplifiers less desirable for HF work.

    You brought up a number of good points, If I really thought solid state devices were ready for Prime time on the HF bands, the box in the corner that I occasionally thorw parts in wouldn't have tubes and sockets in it.

    One last item which I was reminded of;
    Many of the HF rigs have little or no regard to proper T/R, R/T transition timing. Some radios like my IC-756 will generate spikes over the radio's rated output on these transitions. The solid state amplifiers are not well suited to deal with these spikes. While the R/T spikes can be easily dealt with with a millisecond or two delay in the amplifier's main relay, the amplifier has no way of knowing when the radio de-keys (T/R transition) without special consideration given to proper timing in the radio.
    For most tube amps this is not a big issue.

    anyway thank you for the thoughtful reply. :)
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