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Author Topic: Goodbye tubes.  (Read 6870 times)
W9IQ
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« Reply #90 on: August 13, 2019, 04:21:34 PM »

Maybe some people have too much on their plate...

- Glenn W9IQ
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- Glenn W9IQ

I never make a mistake. I thought I did once but I was wrong.
KM1H
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« Reply #91 on: August 13, 2019, 05:22:56 PM »

Quote
The LDMOS has more continous, full power operating life (MTTF) than any tube final by several orders of magnitude.

The gating factor in most commercial applications is not the individual device life but rather the operational life of the product it is in. With LDMOS that is just a guess at this point.

Carl
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W9IQ
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« Reply #92 on: August 13, 2019, 05:41:36 PM »

Quote
The LDMOS has more continous, full power operating life (MTTF) than any tube final by several orders of magnitude.

The gating factor in most commercial applications is not the individual device life but rather the operational life of the product it is in. With LDMOS that is just a guess at this point.

Carl

So what is the MTTF under continuous operation of your favorite tube that is used in amateur applications?

- Glenn W9IQ

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- Glenn W9IQ

I never make a mistake. I thought I did once but I was wrong.
K6BRN
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« Reply #93 on: August 13, 2019, 06:16:14 PM »

Glenn (W9IQ):

Quote
Maybe some people have too much on their plate...

- Glenn W9IQ

Ack!  OK.  Definitely got a chuckle out of THAT one!

Quote
The LDMOS has more continous, full power operating life (MTTF) than any tube final by several orders of magnitude.

Yes.  It is almost certainly true just by the nature of the devices (tube vs. transistor wearout curves).  This is, in fact, a REALLY silly debate.  If Carl likes tubes and believes them to be the best, most reliable device family there is there is, so be it for him.  It's just "Carlworld", as usual.  No need to grid (sic) your teeth over it.

Brian - K6BRN
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KM1H
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« Reply #94 on: August 13, 2019, 06:20:44 PM »

Quote
So what is the MTTF under continuous operation of your favorite tube that is used in amateur applications?

- Glenn W9IQ

Try to stay on track as this thread keeps bouncing around. A tubes life has nothing do do with this segment

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KM1H
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« Reply #95 on: August 13, 2019, 06:23:42 PM »

Quote
Yes.  It is almost certainly true just by the nature of the devices (tube vs. transistor wearout curves).  This is, in fact, a REALLY silly debate.  If Carl likes tubes and believes them to be the best, most reliable device family there is there is, so be it for him.  It's just "Carlworld", as usual.  No need to grid (sic) your teeth over it.

Brian - K6BRN

Grow up Brian or go away. When you have to resort to multiple insults in two posts you have already lost the argument and respect.
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W9IQ
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« Reply #96 on: August 14, 2019, 03:21:59 AM »

Try to stay on track as this thread keeps bouncing around. A tubes life has nothing do do with this segment

I am on track. You questioned the MTTF numbers for LDMOS. I am now questioning the comparative numbers for tube finals.

So answer the question - if you can. And don't forget to cite your sources. Come on Carl, getter done!

- Glenn W9IQ
« Last Edit: August 14, 2019, 03:29:46 AM by W9IQ » Logged

- Glenn W9IQ

I never make a mistake. I thought I did once but I was wrong.
K6BRN
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« Reply #97 on: August 14, 2019, 07:58:09 AM »

Carl:
Carl (KM1H):

Thanks for your advice, but...

Quote
Grow up Brian or go away. When you have to resort to multiple insults in two posts you have already lost the argument and respect.

If growing up means becoming profoundly negative and calling just about everything and everyone around me "garbage" while insisting everything I have and do is far, far better that anyone else, I'll pass on that, thank you.  It's an old  cliche I never want to become.

Now... what was Glenn's question?  Tube MTBF vs. semiconductor MTBF?  There MUST be a quite a few good web-accessible examples to look at.  Mil-STD-217 would be a good place to start for tubes.  And for semiconductors, MIL-STD-883B is the place to go.  Then, once you understand the technology space, look for published papers on the topic.  Time to crack the books if you'd like to settle this debate in a factual way.

Best Regards,

Brian - K6BRN

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KM1H
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« Reply #98 on: August 14, 2019, 08:04:59 AM »

Quote
I am on track. You questioned the MTTF numbers for LDMOS. I am now questioning the comparative numbers for tube finals.

I did? Show me. Estimations dont count if that device hasnt been in service that long. Some call it a WAG since they know they wont be around to back it up.....for whatever reason.

Also show me the manufacturer published life specs of any of the common tubes used in amateur service today in commercial amps.

Carl
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KM1H
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« Reply #99 on: August 14, 2019, 08:07:11 AM »

Quote
Brian - K6BRN

IGNORE AS A CONTINUOUS HARASSMENT TROLL
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W9IQ
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« Reply #100 on: August 14, 2019, 08:20:28 AM »

Quote
I am on track. You questioned the MTTF numbers for LDMOS. I am now questioning the comparative numbers for tube finals.

I did? Show me. Estimations dont count if that device hasnt been in service that long. Some call it a WAG since they know they wont be around to back it up.....for whatever reason.

Also show me the manufacturer published life specs of any of the common tubes used in amateur service today in commercial amps.

Carl

Estimations? MTTF is a statistical representation. This would apply to both solid state devices and tubes.

I was deferring to you as the tube gray beard to supply the relevant MTTF numbers for continuous operation. As far as I know, they have never been published by the manufacturers.

- Glenn W9IQ
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- Glenn W9IQ

I never make a mistake. I thought I did once but I was wrong.
KM1H
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« Reply #101 on: August 14, 2019, 09:00:42 AM »

Quote
Estimations? MTTF is a statistical representation. This would apply to both solid state devices and tubes.

It is still guesswork when it hasnt been verified no matter what fancy justification or name is used.

Quote
I was deferring to you as the tube gray beard to supply the relevant MTTF numbers for continuous operation. As far as I know, they have never been published by the manufacturers.

Well, you are wrong there as some TX tubes used in CCS broadcast service and some military apps were life rated.

Other small tubes used in non TX military gear had a MTBF rating for the complete unit where it was found that operating the equipment continuously produced the longest life.

Carl
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W9IQ
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« Reply #102 on: August 14, 2019, 10:03:48 AM »

It isn't guess work as much as accelerated life testing.

I still haven't seen any MTTF ratings for tubes that are commonly used in amateur radio linears. Can you quote or reference any?

We could extrapolate for some tubes where the life is dependent upon the cathode but I would rather see manufacturer numbers.

- Glenn W9IQ
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- Glenn W9IQ

I never make a mistake. I thought I did once but I was wrong.
W0BTU
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« Reply #103 on: August 14, 2019, 10:52:12 AM »

Shame on you mean fellows for picking on gentleman Carl.   Smiley

On hamSE, that would absolutely not be tolerated! Right, Glenn?
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K6BRN
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« Reply #104 on: August 14, 2019, 01:21:22 PM »

Hi Michael (W0BTU):

Good to see you have a sense of humor, too.

Glenn (W9IQ), Carl (KM1H):

To help you out a bit, I went into MIL-HDBK-217E "Reliability Prediction for Electronic Equipment" and ran the numbers, just as a starting point.  It's on-line.  Anybody can download a copy and repeat the calculations below.

MIL-HDBK-217E has been around for decades and spans the tube, bipolar transistor, JFET and MOSFET eras.  For years, it was the "bible" of reliability prediction and was required reading for all trained electronics technicians in the Army, Navy, Air Force, etc. and also widely used in the Aerospace industry.  It is still referred to from time to time, even though better "initial estimate" methods exist today.

The handbook was written specifically as a "reliability made easy" starting point and standard reference, with its reliability coefficients drawn from extensive in-service life results collected over many years by industry and the government.  It's NOT the most accurate way to calculate reliability - but it gets designers "in the ballpark" very well, for the device classes it covers.

Since Carl is a former Navy radio tech, this SHOULD be a source he respects.  Since Glenn is heavily data and analysis driven, he should feel comfortable with this approach as well, AS A VERY ROUGH COMPARISON AND SANITY CHECK.

That said, I took the MRF-150 transistors in my Yaesu Quadra amplifier as the semiconductor to compare against - it has been the RF power MOSFET of choice in amateur radio solid state HF amps for decades and is very representative of a mature, well known device in wide amateur service.

Fot the tube HF high-power amplifier device, I chose the 572B/T160L in my SB-200, which has also been VERY popular in similar service for perhaps 50 years.  Even the power rating is comparable to the MRF-150.

Apples to apples.

Next, I assumed the very lowest grade of plastic MRF-150 transistor, running at a junction temperature of 100C, continuously (full power).  Continuous, max temperature operation is generally the worst-case for MOSFET transistor reliability and is VERY conservative compared to the occasional, intermittent duty cycles seen in amateur service.  So I stacked the deck against transistors.  A LOT!

For the 572B/T160L I assumed full power, continuous operation, with zero penalty for thermal shock and mechanical vibration - the Achilles heel of tubes, which is seen a LOT in amateur radio applications.  Continuous operation is where tubes are at their very best for in-service reliability.  So I zeroed out tow of their primary failure mechanisms and emphasized a key tube strength.  Every advantage to the tubes.

Doing the (very simple) arithmetic in the Handbook FOR THIS APPLICATION yields the following FIT rates (Failures In Time - per billion hours) - a lower number is better and MTTF is the reciprocal (in hours of the FIT rate):

MRF150 MOSFET transistor (worst case assumptions):  4,262 FITs
572B/T160L tube (under best case assumptions): 75,000 FITS


So, as a starting approximation, giving every advantage to the tube, the transistor is (very generally) at LEAST 18x more reliable than the tube.  Add in realistic thermal and mechanical shock derating for the tube and that difference reaches and exceeds 100x.  And, if you repeat the excercise, you'll discover that similar numbers can be produced for the for the 3-500Z, 3CX800, 1000, etc.

One note... I've found parts manufacturers data sheets to normally be more optimistic than MIL-HDBK-217, as you might expect, and their FIT rates are sometimes given only as a (much lower) base rate that need to be scaled up either by their own derating factors for use and environment, or by the factors given in MIL-HDBK-217.

Makes no difference, because in this excercise we are only interested in the approximate RATIO between tube and transistor reliability, for typical components used in amateur radio.  And our conclusion from this excercise is simply:  Transistors are (pretty obviously) WAY more reliable than tubes.

Big surprise.

Maybe it's time to debate something else?  Just a thought.

Best Regards,

Brian - K6BRN

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