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Author Topic: Goodbye tubes.  (Read 6860 times)
K6BRN
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« Reply #75 on: August 12, 2019, 02:52:30 PM »

A few comments about Voyager...

There have been quite a few failures in the spacecraft electronics, none fatal so far.  And the thermoelectric generators are close to exhaustion, even at minimal power draw.  At some point the sun sensor will lose lock and the power will drop just too low, and they're gone.  But they HAVE been a remarkable success.  The CPUs are Silicon on Sapphire parts that are rad hard and run at (it's been a while, here...) about 10V in this application (16V is also running around in the back of my memory for some reason)  Initially there were three voted CPUs, now they are operating in stand-alone mode, one at a time, last I heard.  I believe the RF amp for T&C is an SSPA.  And yes, capacitors are problematic - especially tantalum types.

GEC/Plessy made some of the semiconductor parts, Hughes Silicon Operations (now long gone as well) made others.  SoS was a major space process back then.

Regarding heat in spacecraft electronics - they get pretty hot, which is one reason why heat pipe cooling is commonly used and why the preferred part temperature grade is 125C.  In a hard vacuum (great insulator), cooling is all by radiation from the spacecraft body while the best internal cooling is by conduction (hence, heat pipes).  Often, one side of the spacecraft broils while the other freezes.  Heaters are commonly used when electronics are powered down or in "cold" trajectories.  Same with the Mars rovers. Hughes "spinners" solved a lot of this problem by rotating the entire spacecraft to provide axial stabilization AND equalize thermal loads.  Great products.

On Glenn's comments - he is right in that both the shelf life and service life of solid-state devices usually far exceed that of tubes.  For one, hydrogen and helium infiltration is much less of an issue.  Most consumers spend zero time tinking about that, but its a real problem and happens wheter or not the tube is energized.  Metal cased tubes are pretty good in that regard, glass enveloped tubes, not so much.  Regardless, LDMOS teachnology is new, and when I was talking about "other failure modes" I was talking about the ones not yet adequately characterized and analyed that exist within the transistor structure itself.  It's not just the junction.  And there are embedded protection and parasitic devices on the transistor die itself, metallization and passivation.  They all have their own failure modes to consider.  LDMOS is still too new to have accumulated adequate failure data, via testing or in-service results, hence they are NOT generally found in HiRel applications.  But maybe one day...

Brian - K6BRN
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K6BRN
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« Reply #76 on: August 12, 2019, 02:54:13 PM »

....Forgot to mention, the CPUs are the venerable 1802 microprocessors.  Look up RCA COSMAC 1802.

Brian - K6BRN
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K4EMF
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« Reply #77 on: August 12, 2019, 04:03:50 PM »

I take it we're WAY past the point of just agreeing that both tube and solid state amps have advantages and disadvantages and which is "better" depends on how it's used and user preferences?

 
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K6BRN
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« Reply #78 on: August 12, 2019, 07:35:13 PM »

Jay (K4EMF):

Quote
I take it we're WAY past the point of just agreeing that both tube and solid state amps have advantages and disadvantages and which is "better" depends on how it's used and user preferences?

Yep.  This is a hobby.  What you enjoy using is the best choice.  Until the next toy.  Then THATS the best.  Smiley

Brian - K6BRN
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G3RZP
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« Reply #79 on: August 13, 2019, 12:29:34 AM »

Brian,

It is slightly ironic that the ICs have longer life than the companies and factories that made them!

There are bipolar Plessey Process 3 frequency dividers in the Voyagers. Process 3 was remarkably rad hard - some radar logarithmic amplifiers assembled onto a hybrid alumina substrate and irradiated to the point where the alumina turned from white to brown (and given four weeks to 'cool' so they could be handled!) still tested out to the full spec.

The joke in the factory was 'Where are the little green men going to park their flying saucer when they come wanting some parts?'
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KM1H
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« Reply #80 on: August 13, 2019, 05:58:19 AM »

Quote
On Glenn's comments - he is right in that both the shelf life and service life of solid-state devices usually far exceed that of tubes.  For one, hydrogen and helium infiltration is much less of an issue.

Id consider that a stretch as there are literally thousands of tubes (lets call them "small signal" or as listed in RCA, Sylvania, GE, and other Receiving Tube manuals) from the 1920's and on that are still 100% useable with no noticeable air ingress. Im sure the thousands of vintage electronics users, ham and otherwise, would agree....me included as I still 'fess up to using them on an almost daily basis and have several thousand on hand.

Larger TX power tubes DO  develop glass to metal seal leaks but they tend to be either type or brand specific. Later WW2 production tended to be built for short and not long term survival but still there are exceptions in great quantities.

Since we dont have ~90-100 year old transistors (or IC's) to compare the subject is moot.

Carl
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W9IQ
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« Reply #81 on: August 13, 2019, 08:25:32 AM »

Hey - I am the one from Missouri. You are not allowed to co-opt our "show me" signature!

- Glenn W9IQ
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- Glenn W9IQ

I never make a mistake. I thought I did once but I was wrong.
W9IQ
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« Reply #82 on: August 13, 2019, 08:37:43 AM »

I was going to say that this is what happens when you live in a vacuum  - but I didn't want you to take that the wrong way...

- 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 #83 on: August 13, 2019, 08:39:17 AM »

Hi Peter (G3RZP):

Good to hear from you again!  Yes...  we've discussed this before...

Quote
It is slightly ironic that the ICs have longer life than the companies and factories that made them!

And it's incredible that some of our space products are headed into interstellar space ... and are still (nominally)... functional.  I will always be proud of that.  As well as the near-earth spacecraft that people use every day ... yet have no idea that their services and safety are ensured by these vehicles.  For the most part, they just work.  It's nice to know we've had a positive impact on the world.

Carl (KM1H):

Quote
Id consider that a stretch as there are literally thousands of tubes (lets call them "small signal" or as listed in RCA, Sylvania, GE, and other Receiving Tube manuals) from the 1920's and on that are still 100% useable with no noticeable air ingress.

Nothing moot about the reliability and lifetime advantage of solid-state devices vs. thermionic valves (tubes).  My career spans the point from when the SAGE (SAC) computer system that once protected the USA to the end of the NIKE era, where Japan maintained their systems well into the '80s.  Both were tube based and I was involved in the latter as a young engineer.  Later, at Hughes, we used a mixture of "tube" devices and solid state, phasing into solid state for their inherent ruggedness and reliability.  I had an entire Specialty Engineering team in my organization before I retired, and am working with reliability & components engineers again, today, in Career Mark II.  Every product I design or help design is all about reliability.  With modern Hi-Rel devices (and even 20 year old ones), solid state wins in the reliability tests (accelerated life tests) almost every time.  And I say almost, because there are devices that you probably would not even recognize as tubes (such as specific types of purpose built TWTAs) that are so good, their useful lifetimes used to overlap with emerging SSPA technology.  Not so much anymore.

Easy to check... look up the MTBF of the tube based SAGE computer system vs. the early IBM System/360's.  It's part of the historical record.  There are literally orders of magnitude differences in reliability.

Quote
Since we dont have ~90-100 year old transistors (or IC's) to compare the subject is moot.

But we do!   Every manufacturer of Hi-Rel and every space company has bushels of transistors (and other devices) that technically have more than 100 years of service life on them, via hi-temperature, hi-voltage Accelerated Life Testing.  It's traditional to screen every lot of parts before the remainder are used and to CHARACTERIZE their wearout curves before they are designed in.  We used to take the survivors home for projects.  I still have boxes of them.  Pretty tough devices, if properly built.

LDMOS is still too new to have an adequate base of information in this area, for HiRel applications, and devices in this technology are evolving very rapidly.  Does NOT mean they are bad - they're probably excellent, based on very early indications.  Just need more data to analyze from multiple manufacturers to fully understand their capabilities before putting them in zero-maintenence systems and expecting them to meet specs for more than 15-40 years with >90% confidence.

Brian - K6BRN



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K6BRN
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« Reply #84 on: August 13, 2019, 08:44:06 AM »

Good Grief, Glenn!

Quote
Hey - I am the one from Missouri. You are not allowed to co-opt our "show me" signature!

Quote
Insert Quote
I was going to say that this is what happens when you live in a vacuum  - but I didn't want you to take that the wrong way...

- Glenn W9IQ

You're evolving a sense of humor!  Bravo!  Excellent! (and I DO mean this!)

Discussions will be MUCH more fun, now.

DE Brian - K6BRN

(Ever trying, ever failing comedian.  But its the "trying" part that counts!)

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G3RZP
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« Reply #85 on: August 13, 2019, 08:45:22 AM »

Mullard OC170 and OC171 germanium VHF transistors are notorious for failing after 30 to 40 years because of whiskers growing in the metallisation and shorting the junction. Then there was 'purple plague' and 'white plague' in integrated circuits causing failure. Another failure we had in dual in line plastic devices occurred when the assemblers in the Philippines changed from a powder filler for the plastic to very short glass rods: moisture crept down them and led to metallisation corrosion. Of course, the assemblers hadn't told us...
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N0YXB
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« Reply #86 on: August 13, 2019, 09:47:33 AM »

I was going to say that this is what happens when you live in a vacuum 


That's a good one, thanks for the chuckle.   Smiley
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KM1H
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« Reply #87 on: August 13, 2019, 10:24:46 AM »

Germanium transistors are notorious for excessive leakage these days and millions of them were in all sorts of applications, including military, in the US, UK, etc. Same thing with the SS diodes. And it includes those still new in original packaging.
Yet vacuum tubes of the same era and earlier are 100% out of the old box. Plug n Play.

Even the F-16 still uses them.

Repeating tales of old spacecraft SS is interesting but proves nothing since they are such a tiny meaningless special application percentagewise and many that are still working are well past their usefulness.....just more space garbage. Plus what is used in the TX amp stages?

Hollow state has also played a part in radiation hardened NASA computers in recent years.

Carl





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K6BRN
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« Reply #88 on: August 13, 2019, 02:48:09 PM »

Hi Peter (G3RZP):

Quote
Mullard OC170 and OC171 germanium VHF transistors are notorious for failing after 30 to 40 years because of whiskers growing in the metallisation and shorting the junction. Then there was 'purple plague' and 'white plague' in integrated circuits causing failure. Another failure we had in dual in line plastic devices occurred when the assemblers in the Philippines changed from a powder filler for the plastic to very short glass rods: moisture crept down them and led to metallisation corrosion. Of course, the assemblers hadn't told us...

Yep... very much remember the tin whisker problems, "purple plague", etc., which is why LDMOS is not yet mature enough for HiRel applications.  Still lots of reliability unknowns.  As I said, not a black mark, just need more time, test data and analysis.  Still.... 30 to 40 YEARS to failure.  Not too shabby.

Carl (KM1H):

Quote
Repeating tales of old spacecraft SS is interesting but proves nothing since they are such a tiny meaningless special application percentagewise and many that are still working are well past their usefulness.....just more space garbage. Plus what is used in the TX amp stages?

(Sigh!).  You do realize that there are more spacecraft in orbit and in service today than ever before in history, and that you use them every minute without ever being aware of the massive number of services they provide?  Perhaps not.  That's called "success", in my business, BTW.

Per your question, we use transistors in every stage of the TX chain, from small signal to SSPA.  Just like cell towers do.  TWTAs are still there in older and specialty payloads, but are fading to the background in favor of SSPAs, often in phased array antennas.  And although SSPAs are emissions type devices, they do not look, smell, work like or feel like a 3-500Z, 6146, T160L or any other of your favorite tubes.

About reliability ...

HiRel and space is all about, well... reliability.  Often (but not always) the items characterized for HiRel are the same devices you use every day, just screened to a different standard.  So that's where the data and analysis is.  And it says you are wrong.  No need to prove it. It's been done by the IEEE, XRTC, ESA, NASA, "Circle A" and many, many other respected technical bodies.  Tube based systems and devices are generally orders of magnitude less reliable than solid state.  Hard to argue with that big a difference, regardless whether or not a few 1920's tubes still flicker to life in niche hobby applications.

Technology will move on one day.  but today, we are in the solid-state era.

About computers based on tubes.  You mean nanoscale ionic switches (which, oddly enough are STILL called "transistors")?  Not tubes.  And not here yet, either.  We'll have to wait and see what happens over the next 20 years or so.  Personally, my bet is on Duotronics.  Smiley

For a number of years my team virtually owned the market for PPC750 based very high performance bus and unit computers for space.  Now, in Career Mark II, I buy computers for space.  Plenty of suppliers.  Have yet to find a single tube in any of them.

You seem to label a lot of things you do not understand "Garbage".  Which indicates you are not open to learning in these areas.  Maybe you should reconsider - life and technology is moving on, and its much more fun to move with it.  Really.

Best Regards,

Brian - K6BRN





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W9IQ
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« Reply #89 on: August 13, 2019, 02:51:29 PM »

This has become a strange mix of shelf life vs operating life comparisons.

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

- Glenn W9IQ
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- Glenn W9IQ

I never make a mistake. I thought I did once but I was wrong.
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