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Author Topic: Will New Power Transistors End the Need for Tube Amplifiers in the Future?  (Read 22025 times)
K2ACB
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« on: January 22, 2012, 05:24:02 PM »

I am far from an expert on hf amplifiers. I have owned tube hf amplifiers and presently own a Tokyo Hy Power Solid  State amplifier.

I have been in touch with a radio amateur who is known for his prowess with innovative techniques in amateur radio including the use of solid state amplifiers. His experimental designs have been displayed at the Dayton hamvention.

This radio amateur who was very helpful to me with regard to a problem I had with my Tokyo Hy Power amplifier told me that he is now working on a prototype for a solid state amplifier using new power transistors from Motorola.

He told me this new transistor which is already on the market and can be purchased for around $270 a piece is the MRFEGVP1250. Each one of these transistors has an output of 1250 watts. Motorola also makes a similar transistor at 600 watts that is less expensive . It is the MRFEGVP600.

I do not know that much about transistor technology but he told me this transistor uses a new technology to get that much power. The transistors can be used from 160 meters to 6 meters as well as on the VHF and some UHF frequencies, However you cannot use them in an amp covering hf and vhf-uhf frequencies. You would need to build two seperate amplifiers,one for hf and another for VHF-UHF.

All it would take are two MRFEGVP1250 transistors to build a legal limit hf amplifier. You could always add more of these transistors to get a better IMD at the legal limit of 1500 watts for an hf amateur radio amplifier. I was also told that these are rugged transistors and you could keep them keyed down for some time as you can for some tube amplifiers like the alpha amplifiers.

This fellow told me once he gets his prototype built he has heard from a manufacturer of commercial amplifiers . They are interested in possible building and marketing solid state amplifiers using his design and  these  new transistors.

It seems to me with the price of some ceramic tubes going through the roof so to speak ,this transistor seems very reasonably priced. For $540 you can have two transistors that will give 2500 watts output. For $1000 you could have four of these transistors that would put out 5000 watts. If you wanted to go to a smaller output you could use the less expensive and similar transistor the  600 watt output MRFREGVP600.

The top of the line amplifiers on the amateur radio market running the legal limit are now costing between $5000 and $8000 including tube and solid state amplifiers from Alpha ,Tokyo Hy Power,SPK and other manufacturers. Some of these amplifiers also have built in tuners which adds to the price.

There is also the Prometheous amplifier that is solid state and weighs more than 150 pounds and will run more than 3000 watts. This amplifier costs over $12000 and is well beyond the expense account of most radio amateurs. With these new transistors it might be possible to build an amplifier much smaller and lighter than the Prometheous with just as much power and half the price. 

But I do not know why ,if these new transistors which are on the market now and which will be the wave of the future, a manufacturer of radio amateur amplifiers could not commercial produce for the Amateur radio market a full legal limit amplifier using these new transistors?  These solid state  amplifiers could compete in price with the  most expensive tube amplifiers that companies like Alpha and QRO are making. Maybe even Alpha now will make an amplifier using these new transistors?

Except for glass tubes that are being made by the Chinese like the 811's,572's and 3-500Z ceramic tubes are becoming more and more expensive. Also I have heard that there are no more commercial amplifiers including medical devices like MRI's that still use tubes.Some of these devices like MRI's  are running a lot power and this power. all this power is now being generated  is generated by solid state devices. Thus tubes like the 3cxpx800a7 pulse tube that was used in medical MRI machines is no longer being manufactured. I also understand that even the Russian tubes like the GS35B and other power tubes used by the Russian military  are no longer being manufactured though their maybe a large supply of these tubes lying around.

I bring this up because if the new MRFEGVP1250 and its little sister the MRFEGVP600 are now on the market and reasonably priced should it not be in the near future that most amateur radio amplifier manufacturers including Alpha and QRO will start building solid state amplifiers using these transistors  and perhaps newer ones that will come out on the market in the future. Will it also be possible using these transistors to improve the IMD of solid state amps?

If anybody has any comments on these transistors and their use in amateur radio amplifiers ,please make your views known.

73
Alan-K2ACB

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M0HCN
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« Reply #1 on: January 22, 2012, 05:36:00 PM »

It's been discussed here before.
One thing to note is that the power device is NOT usually the major expense in a SS amp, power supply, cooling and output filtering are.

Solid state is gradually becoming a more price competitive option, at least for medium power applications, but note that cooling is a MAJOR headache with high power solid state (Far more so then with something like an external anode tube), also you will likely need to budget for an (expensive) tuner with a SS amp where the Pi match at the output of a tube PA will match anything reasonable.

It is not the case that the costs and complexity are in the same places with the two technologies, so just looking at the price of the sand is not that informative. 

Regards, Dan.
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K2DC
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« Reply #2 on: January 22, 2012, 09:07:57 PM »

Yes, heat is the enemy.  But for solid state amps it's not just heat, but heat density.  Take for example a single ceramic tube amp and a single-device solid state amp, both running the same power output and at the same efficiency.  The tube can dissipate the heat over the entire surface and all of the fins of the external anode - many tens of square inches.  The solid state device will be generating the same heat at the junction of the device, over a small portion of a square inch.  Removing that heat creates a mechanically much more complex design with close attention to material selection, thermal resistances and robust and precise interfaces between the materials.  I was not a device-level design guy before I retired, but I worked with many who were and it can get very tricky.

But the answer is yes - In the long run the designs and the device manufacturing processes will mature, and solid state amps will eventually run tubes out of their usefullness.  But there's no telling how long that will take.

73,

Don, K2DC
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N4FBW
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« Reply #3 on: January 22, 2012, 10:03:54 PM »

There are a couple things to keep in mind about solid state amps in the Amateur service:

Market share-linear amps are not a high volume item by any stretch, so it's hard for a company to recover its R&D costs when bringing a new solid state amplifier to market. This is part of what makes SS amps quite expensive.

RF 'worthiness' of the solid state device-There are many high powered MOSFET devices out there that do indeed amplify RF but they are intended for the medical market. In addition, IMD characteristics are a real concern with many  RF transistors. A designer may indeed be able to get 1200 watts out of one device, but that RF had better be clean!

Cost-Tube amplifiers can be had for quite a bit less than solid state amps. Yes, the tubes are getting more expensive but until the prices exceed everyone's comfort zone, tube amps will continue to survive.

Complexity-Solid state amps need filtering, protection circuits and high current power supplies. All of these items add to the cost and complexity of the amplifier. Tube amps are a quite a bit more simple.

Yes, solid state devices will ultimately take over tubes in amateur radio amplifiers but the change is going to be rather slow. Thirty years ago when I was in the hobby, tube amps were really all we had. Thirty years later, tube amps are still around although there are solid state options now. For me, I prefer solid state amps. I've built and worked on tube gear (mainly Heathkit) and helped a friend of mine build an SB-220 back in the day. The brightly glowing filaments of a pair of 3-500z's is something to behold, but I'm much more comfortable with solid state Smiley
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G3RZP
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« Reply #4 on: January 23, 2012, 02:41:58 AM »

The capacitors and inductors in the output filters will need to be rated for a lot of RF current, and won't be that cheap. They too may well need cooling.
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VE7RF
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« Reply #5 on: January 23, 2012, 04:01:43 AM »

You still have several problems with SS.  You can't miniaturize the watt. Ceramic tubes will operate happily all day at 250 deg C. [482 deg F].  SS devices will blow up in your face well b4 that.  Most of these SS devices have LOUSY IMD..and are really ISM devices, used in non linear service..like Class C..where eff is higher.

SS amps require a high power, 2 kw rated LP filter for EACH band! [ well you need at least 5 of em to cover 160-10m]   A tube amp requires NO LP filter's at all.   The SS amp also requires the automatic mating 2 kw rated auto tuner!   The tube amp doesn't need an auto tuner.  The tube amp will  pump out full bore suds up to 3:1 swr.   The SS  amp will either throttle it's power way back, IMD will get worse...or it will just blow up.   The SS amp requires the heavy duty switching supply..which also must be well filtered  for  RFI hash across the hf spectrum.    The latest 52 vdc  switcher's  used by telco's and cell sites are tiny things...and 6 of em will  fit a 25" wide rack.  They are only 6"  tall x 13 "  deep.  Each one is good for 3.3 kw CCS..and barely run luke warm.   They will  operate on anything from 180-310 vac..and any freq  from 40-70 hz.   Cheap too..at $475.00  each.   They even.."talk" to each other. Shut one off..and the remaining 5 of em take up the slack.  the current between em, always divides equally.  The Power factor is perfect too, like well > .99   No harmonics  back into the 240 vac line either.

OK, the eff on those SS amps is lousy at best.  Like 50% max.   Now if you reduce the power to 1/2 rated output, eff drops to a miserable 35%.   The only way to run em at reduced po is to reduce the vdc on em.  And that will also make the imd even worse.  So you solve one problem and create another problem.     The SS devices need a 2 kw rated  broad band combiner.    Have fun getting a combiner to work on 160-10m.  Tubes don't require any combiner.   Tubes will provide far better IMD.  My 3CX-3000A7 is  -59db IMD3.   2 x 3-500Z's is  -46 db pep  IMD3.  Any 3CX-3000A7 is also rebuildable, for 1/2 the cost of a new tube.  SS devices go into the nearest dumpster.   

Command technologies, has signed a contract with EIMAC, who will  be providing em with loads of EIMAC  3CPX-800A7's  The pulse rated versions are good for 3.6 kv.   They are also still being used by FM broadcaster's  world wide, usually in 1 or 2 x tube configs for either 750/1500 CCS output. Years ago, Eimac suggested to FM broadcaster's to switch to the pulse rated version, since they are rated higher for plate V..and then, less trbl with transients/spikes from bad incoming commercial ac power in some countries.  In some places, the line V was so high at times, it would take out the tubes.

To get a clean 1.5 kw pep out... you really need SS  devices rated for 5 kw.  Then the cooling/power supply, combiners, LP filters, auto tuner, only has to be rated for 1.5 kw. 

For the same $540.00  you can still buy a chinese 8877  that will blow the doors off your SS devices.   I can't see  SS taking over any time soon.  The 1st SS  kw ham amp came out well > 30 years ago.  Tubes are still here...at least for a while longer.

later... Jim  VE7RF
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AD4U
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« Reply #6 on: January 23, 2012, 05:37:04 AM »

"One day" solid state devices will completely replace vacuum tubes in ALL applications.  The only valid question is "when" that will happen.

Like previously posted, getting rid of heat is the issue. The heat generated in a typical very small PN junction is much harder to dissipate than the same amount of heat generated inside a vacuum tube.  

Heck I could make a plastic 2N2222A transistor produce 1500 watts IF I could dissipate the heat.

Dick  AD4U
« Last Edit: January 23, 2012, 05:39:37 AM by AD4U » Logged
G3RZP
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« Reply #7 on: January 23, 2012, 06:31:49 AM »

Back when I first started earning a living in professional  radio engineering, there were those who said that there would be no requirements for valves (as we call them over here) for any application except maybe replacements after 1980.......

Solid state would be more efficient, smaller and lighter......

It's when you get to RF power that the problems come. Although solid state has made a big difference in power supplies, I will admit. No more steel tank mercury arc rectifiers for example.

But those low pass filters will be reasonably big, come what may, with capacitors needing to be rated around 7500 VA or more. The inductors won't be weeny toroids either.
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K8AXW
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« Reply #8 on: January 23, 2012, 07:30:57 AM »

RZP:  I'm surprised that nobody has come out with liquid cooled solid state modules!

That would be an intersting concept.
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W6RMK
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« Reply #9 on: January 23, 2012, 07:32:51 AM »

Interesting, too, that you're comparing "no-tune" SS amps with "must tune" tube amps..

That's the reason for the big LPF needed on SS and partly for the low efficiency.

One could build a "must tune" SS amp, increase efficiency, and probably do away with a lot of the downstream filtering, however, it would be tricky.  Probably the biggest problem is that the "margin for error" on the semiconductor device is small, so the tuning would have to be automatic.  Unlike a tube, where you can wait seconds for the operator to turn the knobs, the tiny piece of refined sand will return to it's original state.

There are, of course, some fundamental differences in term of device input and output Z (high for tube, low for SS) which would affect the kind of tank components, etc.

But those problems could be solved (and are.. there are plenty of very efficient narrow band SS amps out there.. and what is a switching power supply these days but basically a high power RF amplifier). That's what Class E/Finv is all about, too.

The real thing is that there is no market for such a device at a price that hams are willing to pay.  Hams who comment (for all I know, Icom sells thousands of kW SS amps a year, but based upon forum comments, tubes are more popular) seem to be willing to trade  a lot of time and skill manually controlling an amplifier for a lower sell price: and that's a conventional tube amp.  

Customers who value time and reliability either go with autotune tubes or SS. Except in experimental situations, MRI, Plasma furnaces, HF comm links, etc. aren't going to be using manually tuned amplifiers.

In the commercial world, tubes tend to be used for very high powers over SS.  There's a fair amount of cost of the amplifier that is related to the number of active component, so it's usually better to use one big tube than lots of little tubes or transistors.  (the broadcast transmitters with multiple SS modules forming what is much like a high power RF DAC are sort of breaking that mold... but part of the appeal there is lower maintenance costs and more reliability, particularly in "degraded mode")
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W6RMK
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« Reply #10 on: January 23, 2012, 07:37:08 AM »

RZP:  I'm surprised that nobody has come out with liquid cooled solid state modules!

That would be an intersting concept.

Having worked with some of the Ixys parts, liquid cooled:  There's still problems with getting the heat out of the die and into the coolant.   And given the high thermal resistance of the package, we're not talking about coolant at room temperature.. it has to be much colder in order to keep the Tj at something reasonable. So now you have a chiller (not to mention the mess of liquid in the first place)

From a cooling standpoint, tubes are easy: they can run hot (which helps the heat flow..) and they have large surface area (good for both radiation and conductive cooling).   That plate glowing red can reject a lot of heat by radiation: the T^4  term is a big deal.
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K6AER
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« Reply #11 on: January 23, 2012, 08:09:12 AM »

One of the larger problems with solid state high power amplifier is FCC compliance. For any amplifier over 21.45 MHz the harmonics must be clean out to the tenth harmonic. Also the harmonics must not only be 43 dB down the primary signal but must meet TIA-603C which is a commercial specification for amplifiers. The harmonics must now be down from the peak carrier at 43 dBc plus the log of the peak  power.

That is about -71 dBc at 1500 watts for not only the conducted harmonics (coax spigot) but the case radiation (cabinet) must also be down by the same amount. Solid state devices have terrible IMD unless you build an amplifier capable of twice the user rating. Most second harmonics are at best about 10 dB down. This means in a high power situation instead of a low pass filter you must use a Diplexer to terminate the second harmonic energy which can be as high as 200 watts on a 2 KW amplifier. Just reflecting it back to the solid state devices will just add more to the mixing equation.

Also the magnetics of splitters and combiners are a problem operating over many octaves of bandwidth. The byproduct is insertion loss and at these power levels this translated into heat. The only way to get red of heat is with lots of air. Now you have a 140 lb. hover craft making 90 dBa of noise.

Items such as the power cable from the power supply to the amplifier must also be down -71 dBc out to the tenth harmonic. When you get out to the antenna range you find out most amplifier designs are like a screen door in a submarine when it comes to RF shielding.

Another problem with solid state devices is there is no guarantee that the devices will be available for any length of time. The hamster market is just too small for multiple manufactures to provide a 20 year supply. On top of that as a group we are a cheap as it comes. We are unwilling to pay what it cost to build one of these amplifiers which for a 3 KW unit will cost more than $12,000 per unit.

There is only one solid state amplifier capable of 2 dB of head room from their rated output and to my knowledge the Dishtronix Prometheus solid state amplifier. It  is only type accepted to 15 meters. They say it can be Amateur modified  for 12-10 meters but the FCC will no longer allows that for new amplifier designs.

Another problem with very high power designs are the power supplies. You either use very expensive switch mode supplies or you use a analog transformer design when you boat is in dry dock and no anchor is needed.

Unfortunately, solid state very high power is no panacea unless cost is no object.
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W8JI
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« Reply #12 on: January 23, 2012, 09:26:50 AM »

This radio amateur who was very helpful to me with regard to a problem I had with my Tokyo Hy Power amplifier told me that he is now working on a prototype for a solid state amplifier using new power transistors from Motorola.

Motorola has been out of the RF power semiconductor business for a long time. Did someone else assume their name?

Quote
He told me this new transistor which is already on the market and can be purchased for around $270 a piece is the MRFEGVP1250. Each one of these transistors has an output of 1250 watts. Motorola also makes a similar transistor at 600 watts that is less expensive . It is the MRFEGVP600.

I find nothing on a Google search for those numbers.


Quote
But I do not know why ,if these new transistors which are on the market now and which will be the wave of the future, a manufacturer of radio amateur amplifiers could not commercial produce for the Amateur radio market a full legal limit amplifier using these new transistors?  These solid state  amplifiers could compete in price with the  most expensive tube amplifiers that companies like Alpha and QRO are making. Maybe even Alpha now will make an amplifier using these new transistors?

Transistors have never been the problem. Not since the 1980's.

The problem has been cooling, cost, reliability, and power supplies.

Can you post a link to these transistors, since Google cannot find anything?

73 Tom
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K5DN
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« Reply #13 on: January 23, 2012, 09:45:32 AM »

If you replace the G with a 6, you get close to a real part number:

MRFEGVP1250 -> MRFE6VP1K25H ?

Bob
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W8JI
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« Reply #14 on: January 23, 2012, 11:03:59 AM »

If you replace the G with a 6, you get close to a real part number:

MRFEGVP1250 -> MRFE6VP1K25H ?

Bob

I wondered if he was talking about Freescale, but he said Motorola and it appears to be a Motorola part number, of sorts.
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