On 5/3/2012 8:03 AM, Jim Thomson wrote:
> Date: Thu, 03 May 2012 02:34:46 +0000
> From: Manfred Mornhinweg<manfred@ludens.cl>
> Subject: Re: [Amps] Tubes vs. Solid State
>
>
> - Hams are obviously willing to pay 5000 bucks for an amp, so why
> destroy the market by making amps that sell for 700 bucks? The
> intermediate option, making amps that are cheap to make, and then sell
> them at 4000 bucks, probably won't live long with hams. They want to see
> where the cost is.
There are a lot of if's, but's, and other variables, but:
There is normally a lot more money in high volume, medium price than
there is in low volume, high price although that depends on reliability,
difficulty inum build, and the ultimate ROI. A rugged, medium priced SS
device that would allow building an amp with far less protective
circuitry would lend itself well to easy and fast build with minimal
parts. You can always add things like auto antenna selection, antenna
tuner, and other goodies to bring in the "high end crowd".
73,
Roger (K8RI)
>
> ## I can hb a pretty big tube amp for $5000.00 I can do a really
> big one for $7000.00
>
>
> And another technical problem is that my amplifier probably won't end up
> particularly rugged. If you set your mind on it, you can probably blow
> it up just by slowly tuning an antenna tuner through its whole range,
> until you find a setting with sky-high SWR that just happens to create
> high enough drain voltage peaks to fry the FETs. Protection circuits can
> keep FETs alive, as long as the high SWR comes up slowly (milliseconds),
> but if you have a loose connection in the antenna system, that provides
> 1:1 SWR most of the time, but suddenly goes up to a condition that
> causes those high voltage peaks, this amplifier can be blown up more
> easily than one that uses just a few, rugged FETs. The reason is that
> I'm using many small FETs, directly in parallel. That's simple to do,
> and inexpensive, but any overvoltage will make a single FET enter
> breakdown, and that single FET cannot survive the big discharge. When
> using just a few large FETs, which is much more expensive, the big FET
> that breaks down has a much larger chance to survive.
>
> ### Aside from all the typ problems of SS amps, there is even more
> problems. None of em will run full bore rtty, etc into a 3:1 swr !
> So now you require the mating automatic 2 kw CCS rated tuner.You
> don’t need the auto tuner with the tube amp, not mine anyway.
> 5 kw CCS rtty into a 3:1 swr....no sweat. Lets do lunch.
>
> ## With these SS amps, you also require a monoband 2kw CCS
> rated LP filter for each band ! At least a min of 5-6 required
> to cover 160-10m + warc. Plus you have to be able to switch
> them in and out.
>
>
>
>
>> As to home brew, there are very few of us who actually do that be it SS
>> or tubes.
> I can't help it, I worry that this is spelling the end of ham radio. To
> me, ham radio is about being interested in radio technology. I can
> perfectly well accept the fact that not all hams are professionals in
> electronics, but I would expect that all hams, without exception, should
> at least be interested in electronics, and try to learn, at their own
> rate. I just can't understand those people who say they love ham radio,
> but whose love for radio ends precisely at the front panels of their
> rigs! To me, they DON'T really love radio. Instead, they are after the
> utilitarian side of ham radio, such as keeping in touch with friends and
> family, or having emergency communications. In my surroundings, at least
> 90% of hams, and probably much more than that, belong to this group that
> doesn't have any interest whatsoever in electronics. Hear them talk on
> the bands: The weather, the brand and model of their rig and antenna,
> and that's about it. I call them "empty QSOs".
>
> ### ham radio is in its dying years. They hand out ham tickets
> like popcorn, and they still cant give then away. Empty QSO’s,
> that’s at least one step better than 10,000 brain dead contesters
> on every 2nd weekend.
>
>
>
> Of course, anything like that is too complex for the "typical ham", the
> one at whom the ARRL is addressing QST. But even the simplest tube type
> amp is neither for the typical ham, because that typical ham would never
> dare to build anything having 3000 volt in it. Or rather, he would never
> attempt to build anything at all, period!
>
> ### You may be right. No such thing as a slight electrical shock
> with HV. Take all precautions, and its not an issue. My hb RF decks
> are separate from the HV supplies. Each box that has HV or B+ inside
> it, gets it’s own dedicated HV meter...wired directly between B+
> and B-. If the B+ HV fuse blows open in the rf deck, the HV meter
> in the rf deck reads zero. Mean while the hv meter in the HV supply
> still reads full B+. The whole issue when dealing with hv is rather simple.
> You have a better chance of getting mashed in your car by a soccer mom,
> trying to do some texting while driving vs HV accidents.
>
>
>
>
>> I still maintain SS is not ready for prime time, but for those with the
>> knowledge and desire to experiment it's a great field.
> Well, I think differently: I think solid state is the way to go,
> definitely, at the power levels hams are allowed to use.
>
> #### How am I supposed to get 750 watts AM CXR, and 3750 watts
> pep out.... and measured at the feed-point of the antenna..with
> SS. Almost forgot.... that’s into a high swr. Repeat for all bands
> 160-10m, including warc.
>
>
> Only at much
> higher power levels do tubes make real sense. Simply because tubes are
> available for several tens of kilowatts in a single device, while
> transistors are not, and would need to be stacked up in too large
> quantities. But at 1.5kW, and even 10kW and some more, solid state is
> more practical than dealing with tubes and their inevitable
> narrow-banded tuned circuits, their lifetime of a few thousand hours,
> and sockets costing a thousand dollars!
>
> ### say what. A typ 3CX-3000A7 will last 4 years at full CCS
> output. That’s 35,000 hrs...not a few thousand hrs. I use a regulated
> AC Sola constant V xfmr.. that feeds the input of a variac... that then
> feeds the input of the fil xfmr. The new Tube is run at rated fil V,measured
> at the socket for the 1st 200 hrs. After 200 hrs, fil v is reduced to the
> pint
> where the Po just barely drops off a few watts, then the fil v is increased
> by .1 or .2 volt. As the emmision wears down, the fil v is raised up by
> .1 v. When I end up with the fil V at +5%..then send it in to be rebuilt,
> for half the price of a new tube. The socket for a 3CX-3000A7 is cheap.
> The YC-243 has no socket. GG triodes dont need sockets anyway, nor
> does the YC-156. Just bolt the grid flange to the chassis..done. The
> F7 version of the 3CX-3000A7 also does not require a socket. Heck,
> they even make a water cooled version of a 3CX-3000A7.
>
>
>
> One could argue that a lifespan of a few thousand hours for a tube will
> last a ham's lifetime of normal operation. But practical experience
> shows that tubes are less reliable: Among the local hams I know and who
> own power amps, the spread is about 2/3 tube amps, and 1/3 solid state,
> changing fast to increase the proportion of SS. Most of these hams turn
> to me when something fails. Over the last several years I had to replace
> several 3-500Z, and a few other tubes, but not a single high power
> transistor.
>
> ## I know folks with SB-221’s who are still getting full PO
> from the original tubes. I have replaced one pair of tubes
> in my drake L4B linear since I bought it new, back in 1977.
>
>
>
>
> The only time I got a solid state amp for repair, a Quadra
> that had seen extensive contest and DXpedition use, the problem was a
> broken solder joint that took five minutes to find, and one second to
> repair.
> In several tube amps I had to replace electrolytic caps, and I had to
> rewind two power transformers. In SS amps, so far I have seen no power
> supply trouble. Of course, the number of amps that could possibly fall
> in my hands when broken is small, but I believe that it's enough to do
> at least a broad statistic about their reliability.
>
> ### What is the TX IMD on these SS amps you have built.
> That Elecraft K3 xcvr is crap at -29db IMD-3. I don’t think
> their KPA-500 is much better.
>
>
>
>
>
> Years ago I looked into the possibility of making broadband tube
> amplifiers, because I just hate having to retune an amp after changing
> bands or even changing frequency a lot within a band. But I quickly
> found that the tubes' combination of high internal capacitance and
> required high operating voltage makes this totally impossible. Tubes
> force the use of tuned circuits, while transistors give the designer the
> choice between tuned and broadband impedance matching.
>
> ### Using 3-4 x drake L4B amps, all wired nose to tail in series,
> (since they will handle 2 kw on bypass mode), I just tune each
> one up on a different band ! One rotary switch ensures only
> one key line is active at any one time. Simple.
>
> ## the hb 3CX-3000A7 amp and also the YC-243 amp uses
> vac tune and load caps.. + a pair of broadcast variables for the
> tuned input. Separate bandswitch for the tuned input and high
> power Pi net. Each vac cap gets its own turns counter..which reads down
> to .01 of a turn. The pair of broadcast variables get a 4 inch diam, jackson
> bros
> ball drive, which is calibrated 0-100 over a 180 deg arc = 6 inchs.
>
> ## it takes exactly 45 secs to qsy from 15m to 160m. Just dial up
> using pre-sets. 1 pre-set for cw and 1 for ssb on 20-10m. On the
> lower bands its 1 pre-set for cw..and 2 x pre-sets for ssb. The secret is
> to lower the loaded Q a tiny bit. Even with the drake amps, I tune it
> at 14.200 and its good from 14.100 to 14.325 with a flat ant swr.
> I cant squeeze any more out of it by retuning at 14.100 or 14.325
> so just tune it once at 14.200.
>
>
>
>
>
> Tube dissipation ratings instead are true, real, directly usable, as
> long as you assure enough airflow. This difference comes from the simple
> fact that tubes usually have their heatsinks built-in, while transistors
> do not, so transistor ratings have to be given in a way that allows
> equipment designers to calculate the true allowable dissipation, after
> fitting a certain heatsink.
>
> ## large metal tubes are easy to cool. Plus they are usually
> specified with an IN-take air temp of 40-50 deg C. Now
> I put mine in the un heated workshop next door to the shack.
> If Im working in the shop, then the shop gets heated. In take
> air temp is more like 15-20 deg C. Anode diss goes way up.
> Crank up the air pressure, combined with colder air..and it goes
> WAY up. I can easily get another 50% CCS anode diss with that
> technique. For cw-ssb use, the pressure can be turned way down
> of course.
>
> ## whether it’s a tube amp or a SS amp... and it makes noise,
> just put em into another room. Then zero noise in the radio
> room..and no heat either. In winter, heat from the amps
> stays in the basement shop. In summer, its routed to the outside.
>
> ## My other problem with SS is eff. Your typ SS amp operates at a
> lousy 50% max eff..and that’s when run at max output ! Reduce
> the PO by half....and eff will drop down to 35%. At that point,
> you have to reduce the vdc a bit to get the eff back up. The
> problem with reduced vdc is.... the TX imd drops off !
>
> ## a 1.5 to 2kw output CCS SS amp, that covers all 9 x bands, and will
> handle
> a 3:1 swr and LOW IMD, is no simple task. Hats off to anybody who can
> pull it off at any price. BTW,,, these 1-52 kw SS FM broadcast amps you
> see typ
> consist of 1-52 x 1 kw SS modules, with mating switching supplies.
> Then a myriad of combiners. They operate at up to 92 % eff..and are
> NOT linear amplifiers. They operate on a single freq..with a 1:1 swr.
> So don’t use them as some kind of reference or standard as to what could
> or should be done with 9 band ham type SS linear amps.
>
> ## ONE instant on GG triode, no socket, simple un regulated B+ supply
> with a
> tuned pi input and a pi output is about as simple as it gets. You will go
> broke
> trying to get YC-156 power levels from SS. Why not back up one notch..and
> start
> with a LOW imd xcvr that puts out 200 w pep, without going into melt down.
> The K3, with its lousy –29 db IMD-3 and 100w pep out simply does not cut it.
>
> later.... Jim VE7RF
>
>
>
>
>
>
> Note that some solid state devices, such as many diodes and also some
> switching MOSFETs, nowadays are rated for dissipation and/or current at
> a more real-world temperature, such as 75 or even 100 degrees Celsius.
>
>> Depending on frequency we set the internal limit at 100C and max
>> internal operating temp at somewhere between 70 and 90C.
>> dopant migration was starting to become noticeable at 100C so when I was
>> in the industry.
> That's a bit lower than I had known. Anyway one has to keep in mind that
> these phenomena are time-related. A ham amplifier can probably get away
> with pushing the silicon to 150 degrees when delivering full output,
> because this will only be short-term. If the transistors live for 10,000
> hours at that temperature, that should be enough. A broadcaster instead,
> running 24/7 at full power, will want to get much more than 10,000 hours
> of life from his transistors, and so they need to run cooler.
>
> That said, and having done calculations on the thermal aspects of
> widespread ham equipment, I can't avoid the suspicion that many ham
> transceivers run their finals well in excess of 150 degrees internally!
> The typical max ratings are often 175 degrees or even 200 degrees for
> transistors that are NOT encased in plastic. Particularly brave
> manufacturers even specify 225 degrees. I don't know how much of that is
> due to processing techniques that reduce dopant migration. The rest is
> probably based on decisions to accept shorter lifespans as "typical". In
> any case, silicon by itself survives much higher temperatures. It's the
> migration problem that sets a limit, and the attachment of the chip to
> the case (usually by some solder) sets another limit.
>
>> You can also use *cold* or chilled water. Just draw the water out of an
>> open PVC tank and return to the same tank. 20 gallons will run a KW amp
>> for quite a while. Throw in a few chunks of ice and have at it. We use
>> the water in plastic bags for our picnic coolers , so you just grab a
>> couple and drop in the tank
> But one needs to be always careful about avoiding condensation inside
> the amp. At my former job, we had tons of actively cooled electronic
> equipment. There were big coolers to chill the water/glycol mixture just
> enough to keep the outside of the electronic racks precisely at ambient
> temperature, to prevent thermal turbulence. The controllers monitored
> ambient moisture, to keep the water always above the dew point.
> Sometimes something went wrong, and then we got dripping wet
> electronics, with all the obvious consequences.
>
> The coolers were mostly of the plain common compressor heat pump type,
> but in some vibration-sensitive locations we decided to try Peltier
> coolers. They turned out to be a disaster. The place was at 2600 meter
> altitude, the Peltiers overheated due to the low air density, and died
> faster than we could throw them in the trash.
>
>> You can take it down as far as you like as long as you don't get
>> condensation on the circuit board,
> Exactly. And with a typical comfortable ambient humidity of 60 to 70%,
> condensation happens at just about 6 degrees below room temperature!
> It's not worth doing, for such little temperature difference.
>
>> or ice up the pump.
> At any normal room temperature and humidity, condensation will occur far
> sooner than any ice can form. The dewpoint at comfortable room
> conditions is always above 10 degrees Celsius. You would need an
> extremely dry or very cold environment, to get the dewpoint below freezing!
>
>> BTW there is a fungicide used in swimming pools that will do a good job
>> of keeping *stuff* from growing in your cooling system. I'm not
>> referring to Chlorine.
> I will have a look in the swimming pool section of the home improvement
> store! Thanks for the hint!
>
> Manfred
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