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Author Topic: Goodbye tubes.  (Read 7144 times)
SM0AOM
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Posts: 258




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« Reply #135 on: August 17, 2019, 11:03:11 AM »

In the system I supervised, the amplifiers used DC-grounded combining networks and high-pass filters with static chokes between the antenna feedline entrance, switch matrix and the transmitters.

Also, Poly-Phaser transient suppressors using AC coupling were used at the amplifier output connectors, per the advice of the applications engineers at Rockwell-Collins when purchasing the PA-2250 amplifiers.

At the first location of the transmitters, one vertical log-periodic took a direct hit in the late 90s which damaged the balun and the transient suppressor without harming the PA transistors.
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K6BRN
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« Reply #136 on: August 17, 2019, 11:17:55 AM »

Karl-Arne (SM0AOM):

Well, your reliability input seem to be right in line with the MIL-HDBK-217 predictions of a transistor reliability edge of about 20x to 100x, depending on application and environment.  Nice to have yet another independent confirmation.

Brian - K6BRN
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SM0AOM
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« Reply #137 on: August 17, 2019, 12:22:09 PM »

Professional users have today for all practical purposes abandoned tube amplifiers due to operational economy, maintenance and reliability reasons.

An example;

During the final 5 years (44000 hours) of their operational life, the 6 Telefunken 20 kW amplifiers which usually were intermittently operated on the 5 kW level consumed a total of:

- 24 ea 4CX5000A
- 20 ea 4CX250B
- Other spares
- 300 man-hours of scheduled maintenance
- 150 man-hours of non-scheduled maintenance
- 1 500 000  kilowatt-hours of energy

totalling 1 300 000 SEK

Their Collins solid-state replacements consumed the following during their first 5 years

- 60 man-hours of scheduled maintenance
- 40 man-hours of non-scheduled maintenance
- 180 000  kilowatt-hours of energy

totalling 230 000 SEK


Also, it was possible to retire 2 engineers and technicians, and to de-man the transmitter site, only visiting it for a monthly maintenance check.

A financial analysis showed that the investment was paid off in less than 5 years, and that the operations using the transmitters otherwise would have to be prematurely curtailed when the site engineer retired or for lack of spare parts.

Radio amateurs seldom make financial analyses about their investments in amplifiers, but it may be of educational value to compare with enterprises that require profitability...
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KM1H
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« Reply #138 on: August 17, 2019, 01:39:34 PM »

Im glad to finally read some hard facts about properly operated commercial amps, presumably all HF or lower??

Now what about SS ham amps? Has anyone done a study and released the data??? Ameritron, Yaesu, etc?
What ham amp has used the failure prevention techniques as mentioned above?

Carl
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K6BRN
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« Reply #139 on: August 17, 2019, 02:15:58 PM »

Carl (KM1H):

Quote
Now what about SS ham amps? Has anyone done a study and released the data??? Ameritron, Yaesu, etc?

Odd question.  Why would you expect it to be substantially different? 

Because it's obviously not. 

There is still a thriving business in trading, buying/selling HF amplifier tubes as the existing stock shrinks and prices skyrocket.  They ARE consumables.  In amateur HF transistor amps, the final transistors are not considered consumable and usually have FIT rates as good or better than other amp components.  They do not often fail in a SS amp unless there is abuse, an amp design defect or infant mortality.

You saw the MIL-HDBK-217 numbers for the T160L/572B vs. MRF150.  You can run the numbers yourself for different parts, duty cycles, environments, device qualities, plastic vs. ceramic packages, frequency and use, etc.  It's just arithmetic.  Circle A and the various government tech corps took pains to make it simple and easy to use.
 And it has been used to set life and maintenence baselines for thousands of military and areospace systems for decades.   Oddly enough, quite a few off-the shelf amateur tranceivers, amps and receivers have also been used in the combined services for decades, as well as the agencies.

And assuming that all amateurs use their amps the same way is probably not a good bet.  If there IS an "average" amateur use for amps, it's probably "turned off 99.9% of the time".  Which means it'll be the caps that set the MTTF, not the transistors.

Now if you want a precise figure for, say a Yaesu Quadra MTTF or FIT rate in (composite) amateur service, perhaps you could call up Yaesu (or Elecraft, or Icom).  Chances are that they have done the calculations for their own equipment AND have service data available to back it up.  If you ask nicely, they may just tell you.  Then you can let us know.

Best Regards,

Brian - K6BRN


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SM0AOM
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« Reply #140 on: August 17, 2019, 02:50:48 PM »

The field reported MTTF:s and MIL-HDBK-217 figures for PA devices assume proper design and operation of the amplifier that contains the devices. If these criteria are not met, "all bets are off".

It appears that SS amplifiers that are aimed to the amateur markets are designed with smaller margins and with less elaborate protection than professional units in the same nominal power output range, which may lower the MTTF considerably due to catastrophic failures caused by overdrive spikes, self-oscillations or power supply transients.

In order to attain high fielded device MTTF figures, proper design and derating becomes very important.

Trying to get away with "ICAS ratings" for transistor currents and voltages will result in problems. Tubes are much more forgiving to momentary overloads caused by careless operation.

Frankly, the average amateur is not qualified to handle equipment that operates at power levels much above 100 W.
Very few understand the physical limitations for their equipment.
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K6BRN
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« Reply #141 on: August 17, 2019, 06:26:17 PM »

Mmmm.  Yes.  Amateur equipment design quality varies a lot.  From that of Elecraft KPA-500/KPA-1500 quality, where the amplifiers are very consevatively designed (and well done) to the marginal 3-tube MFJ/Ameritron ALS-800 amp design.

Regardless, all bets are off for ANY technology where designs are not properly executed.  Commercial, military or amateur.  And there are brainfarts in every category.

Brian - K6BRN
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K6BRN
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« Reply #142 on: August 17, 2019, 06:39:06 PM »

Regarding "ICAS"...  There is no such legitimate rating, in my mind.  ICAS WAS a RCA marketing rating aimed at the amateur market for tubes to convince them they could sacrifice tube life for power, when Tubes were pretty cheap.  And they could.  Today, when tube replacements are becoming more and more rare, it makes less sense.  It NEVER had any applicability outside of that realm.  Yet I see it attached to antennas, solid-state amps (and probably bananas) where it has no consistent basis or meaning.

It's like "Watts Music Playing Power" for stereo equipment of the '70's and '80s.  A stereo with a 1 amp fuse would claim "1,000 Watts MPP".  At least there, the FTC stepped in and clearly defined "Watts RMS" (no, its NOT literally the mathematical definition of RMS watts - two entirely different things), the test procedure and preconditioning period.  It was a reliable standard and apples to apples comparisons could be made across equipment from different makers.  It worked to bring claims to realistic levels.

Today, ICAS pretty much means "I THINK it'll work, for a very short while at least, at this power level.  Then it will probably catch fire or explode."

Brian - K6BRN
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KM1H
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« Reply #143 on: August 17, 2019, 06:51:43 PM »

Quote
The field reported MTTF:s and MIL-HDBK-217 figures for PA devices assume proper design and operation of the amplifier that contains the devices. If these criteria are not met, "all bets are off".

As anyone who has actually been involved would know.

Quote
It appears that SS amplifiers that are aimed to the amateur markets are designed with smaller margins and with less elaborate protection than professional units in the same nominal power output range, which may lower the MTTF considerably due to catastrophic failures caused by overdrive spikes, self-oscillations or power supply transients.

As to be expected and absolutely no surprise there despite some backround chattering.

Quote
In order to attain high fielded device MTTF figures, proper design and derating becomes very important.

Which costs money and that results in low sales at high prices. It should come as no surprise that Ameritron leads the pack in SS amp sales.

Quote
Trying to get away with "ICAS ratings" for transistor currents and voltages will result in problems. Tubes are much more forgiving to momentary overloads caused by careless operation.

Inadequate cooling is another SS problem in both home and mobile use.

Tube grid damage from momentary overloads has never been adequately examined AFIK. The typical ham is happy if the amp still works after it kicks off. To be clear Im talking about the 8873/74/75, 8877, 3CX800A7, 4CX1000A and similar 0-1W allowable grid dissipation tubes and not a 3-500Z, 3CX3000A7, etc.

Not mentioned by some of the anti tube chattering class is that several of the high power tubes in commercial service can be rebuilt several times at a substantial savings over new.

Quote
Frankly, the average amateur is not qualified to handle equipment that operates at power levels much above 100 W.
Very few understand the physical limitations for their equipment.

So true and so sad yet many of those are the first to claim they know all the answers and create OTA and online dissension with constant posting. IOW, they do not understand their own limitations, often between their ears.

Carl
« Last Edit: August 17, 2019, 06:56:03 PM by KM1H » Logged
W1VT
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« Reply #144 on: August 17, 2019, 07:41:29 PM »

It appears that a lot of solid state TV amplifiers have outlived their useful lifetime with the re-arrangement of TV broadcast frequencies in the USA.  I just saw some ex-broadcast equipment this week!
After having to re-scan the channels on my TV set!
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K6BRN
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Posts: 1339




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« Reply #145 on: August 17, 2019, 08:16:21 PM »

Quote
So true and so sad yet many of those are the first to claim they know all the answers and create OTA and online dissension with constant posting. IOW, they do not understand their own limitations, often between their ears.

Well... its an amateur forum for the radio amateur radio HOBBY and anything goes.  From those who know quite a bit to those who would like to learn (and more or less).  There should be no "pecking order here, just help and support.  At it's very best, ham radio is a service hobby - not just for amusement and emergency comms but also for help, enlightenment and goodwill to our fellow hams and citizens of the world.

It's not like the professional world where livelyhoods and lives are on the line, competence is absolutely required and reflected not in personal claims, but in professional college degrees, professional certification, high compensation levels, high demand for services, revenue bearing patents that allow early retirement, and where there are very real career ending disincentives for poor performance or the inability to work on a team.  Lots or real pressure in that realm.  For real reasons.

Apples and oranges, right?

Brian - K6BRN
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SM0AOM
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« Reply #146 on: August 18, 2019, 01:32:46 AM »

In properly designed and operated SS amplifiers for professional use, it appears that wear-out phenomena of other parts, such as power supplies, come much earlier than any PA transistor wear-out.

The SRT SSA400, that used BLX15 throughout in the driver and PA stages, was a very early (1973) SS amplifier, and had some "teething problems", with bias stability and device encapsulation. After correcting these, they have shown exceptional reliability.

The Danish Navy is into their third generation of exciters for these amplifiers (!), having worn out SRT CTD500 and
Selenia exciters during the 45 year usage term.

Failures due to electrolytic capacitor ageing and similar causes usually begin show up around 100000 hours of accumulated operating time.

Regarding the competence of radio amateurs, I am of the firm belief that amateur radio operators should be held at higher standards than professionals.

No professional operator is allowed to build or modify their equipment, and today's radio amateur has lower examination standards (with Germany as one exception) than the current maritime (GOC) or aeronautical radio operator.

An engineering degree and documented Morse competence should be required for the highest classes of amateur licences. Others should be limited to 50 W and "plastic radio equipment"
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G3RZP
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« Reply #147 on: August 18, 2019, 02:28:17 AM »

So from what Karl-Arne says, professionally, there are a lot of factors in the installation required to protect the SS amplifier against lightning induced EMP. That leads to my next question which is how many SS amplifiers fail in amateur service because of failures to provide such protection?

It seems to me unlikely that Joe Q. Ham will understand the protection requirements, and it's quite possible that an unexpected thunderstorm can occur with the amp switched off but still connected. I lost the front end FET in the FT102 in 1984 to a thunderstorm. I heard thunder as I got in from work, disconnected the VHF rig and there was a flash which was bright enough for me to seeing a purple afterglow for a few hundred milliseconds, a simultaneous loud bang that shook the house and the telephone answering machine started up , and required major repair to get it to work afterwards! That with underground telephone and electrical services....For my home brew amplifiers, I always had the antenna relay 'energise to receive', figuring that the PA tubes could stand the surge when off rather better than the receiver front end.
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SM0AOM
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« Reply #148 on: August 18, 2019, 05:18:35 AM »

It takes a "layered approach" to protect PA transistors (and receiver front-ends) from LEMP.

DC grounding and high-pass filters serve to bleed off the high-energy fundamental of the lightning waveform, transient protectors clip any voltage surges before they can make their way through the filtering.

SS amplifiers need more attention to detail in these matters, as the transistor junctions are more fragile.

The Poly-Phaser transient protectors we used clipped the transient waveform to about 500 V peak, and provided a first-order high-pass filter with about 500 kHz cut-off frequency.
 
The amplitude of a standard 4/20 ┬Ás lightning waveform would be reduced to about 100 V after passing through the network. Frequency responses of the combining networks would reduce it further before it can reach the transistors.

SSA400 amplifiers were connected via diplexers with an integrated matching network to large discones for MF maritime services, which used static drain chokes and the transmitters had transient protectors.

They attracted a lot of lightning, but no PA modules were lost during the 15 years they were in H24 operations, but strikes sometimes blew up mains fuses, SDSL data modems, intrusion alarms and ordinary telephone circuits at the sites.

Fitting proper entrance transient protections, mains line filters and using opto-isolation made the situation much better.

The SSA400s were retired in 2010, and strangely enough, their successors, 1 kW SS transmitters from "down under" were much more susceptible to lightning damage.

I did not work with these transmitters myself, but was told that transients entering through the mains feed was suspected to be the cause.


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K6BRN
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« Reply #149 on: August 18, 2019, 07:52:51 AM »

Quote
Regarding the competence of radio amateurs, I am of the firm belief that amateur radio operators should be held at higher standards than professionals.

You do realize that this is a hobby, it's specifically "amateur" radio, and the bands amateurs are authorized to TX on are miniscule.  In other words, any damage they may do is VERY limited.  For a reason.  It is literally a "playground"

Quote
An engineering degree and documented Morse competence should be required for the highest classes of amateur licences. Others should be limited to 50 W and "plastic radio equipment"

Morse code?  You MUST be kidding.  It has no purpose at all in modern communications.  Even POWs didn't use it to communicate between cells (they used "Tap Codes"). 

I guess I'd be fine (degrees, code certified).  But there'd be precious few people to talk to and the Hobby would be quite dead within a short time.

Maybe we just get along and help each other?  Joe Taylor and his digital communications develpment partner and team are literally setting the benchmark as we speak.  Maybe it's time to ask:  "What have I contributed?"

Best Regards,

Brian - K6BRN

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