About the lifespan of CRT"S - Videokarma.org TV - Video

rca2000 · #1 02-19-2006, 01:08 AM

I see so many old (pre-1960) articles on how CRT's often last only a few years or so. However, personal experience tells me, that many of them will last indefinitely. I just acquired some get tech-tips, and an an article on GE's release of their 110 degree tube in 1959 or so, and how they life-tersted a batch, and found that after 2000hours of continuous use, 75% of the cathode material remained. To them that was not good enough, so they re-designed the gun, and got it to where it had 98% of the material left after the same 2000hrs. That would indicate that the tube would last 10-20,000hrs. or more. So, WHY the pessimism early on about crt life, when we all now they often last almost "forever"(with a few exceptions, which were no good from the start, like 91-99 Zenith tubes, Sony 26" tubes, predicta tubes and so on).?

jstout66 · #2 02-19-2006, 12:22 PM

makes sense. I don't understand why there is such a pessimism on tube life as well. I think it depends somewhat on the design and I am sure luck plays a part as well. This goes against what some believe, but my Uncle who was a repairman for 20 years always said that sets with instant on always had the best tubes in them, which somewhat coinsides with life-span tests. I would assume GE had those tubes running non-stop. 2000 hours would be 142 days of not being shut off. My Uncle believed that a tube that was always on would last longer because there was no shock or voltage variation from warm-up time. Back in the day, most sets that came in with instant-on had very good pictures. (and some of these sets were 10 years old) However he did not like instant on in tube sets. Said that altho it would keep the picture tube good, the rest of the set was getting destroyed from heat. I wonder if the design process playes a big part tho? Has anyone ever seen a bad delta Chromacolor tube? I never have. They just go on and on and on. However it was a different story when they went to the tri-focus in-line tube. Anyway.... I believe that if designed well from the start, CRT's can last almost forever, and I do not believe that instant-on shortens a tubes life.

Yamaha B-2 · #3 02-19-2006, 12:53 PM

Think it all depends on how many electrons they could put in the CRT in the first place. Some manufacturers (RCA, Zenith, etc.) had a propriatary method of putting electrons into the CRT which allowed for very dense packing, while others, like Curtis-Mathes, which didn't have much in the way of a research department, simply poured the electrons in with a ladle (or bucket in the case of larger CRTs). So the high-end guys with the sophisticated electron packing methods always had a much longer life expectancy for their CRTs. Of course, if any of them would spring a leak, the electrons were quickly gone and all bets were off. Hope this helps.

3Guncolor · #4 02-19-2006, 01:43 PM

Back in the 70's I changed a lot of Chromacolor I CRT's. But the Chromacolor II's seem to just about last forever. It seems how hard the CRT is run (briteness) makes a big difference in how long it lasts. Where I work we have some monitors that have been on 24/7 for over 10 years we keep the drive low so they are still in great shape.

Steve

Chad Hauris · #5 02-19-2006, 03:45 PM

It's hard to say what is the most important factor in preserving CRT life...it probably is mostly in the tube itself. I do know that computer monitors tend to last longer when switched off at the end of the work day rather than left on constantly.
The case for instant-on seems to be that it eliminates filament turn-on stress (which it does) but that doesn't seem to be a major problem in tube failure (as it is in light bulbs for example). Most of the problems with weak CRT's seems to be in weak emission; and the instant-on circuit, by keeping the cathode hot, would seem to wear down the emissive properties of the cathode even in the standby state. However, on the instant-on sets I have, out of say 10-15 sets only one seems to have a worn-out CRT.

andy · #6 02-19-2006, 03:54 PM

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kx250rider · #7 02-20-2006, 11:13 AM

A theory which I tend to support is the deterioration of the cathode coating due to foreign gas (air, etc) in the tube. AK member Colortel, an engineer in the field, I recall also supports this theory. Basiclly, the cathode coating, where the electrons are fired from, gets damaged or corroded when the vacuum of the tube is not near absolute. So the more deterioration, the fewer electrons that can get emitted. HOWEVER: The deterioration seems not to happen nearly as badly in CRTs installed in constant filament warm circuits. My personal experience has been that if you have a tube that is starting to weaken, you can keep it alive much longer by rewiring the TV to leave 50 or 60% of the filament voltage on when the TV is off. Worked great in a CT-100! Evidence to this part of the theory is that you can take a perfect working Sony color set from the 1970s (with factory-designed constant filament power) for example... The TV works great with a strong CRT for 20 years, then unplug it for a year and the CRT is about DEAD! Happened to many of my customers...

Bottom line: A CRT new in the box, with excellent vacuum, should stay as new forever. But one with poor seals (15GP22, and any metal/glass combination), or any CRT with less than excellent vacuum (Sony from the 80s/90s, Mitsubishi projection from 90s, etc) will deteriorate no matter what, but can be kept alive longer if the filaments are warm all the time.

Charles

old_tv_nut · #8 02-21-2006, 10:08 PM

There definitely is a difference in manufacturing quality, and I would presume it's mainly due to residual gas, but maybe also cathode quality. When Admiral had a tube plant, they made some of the worst; Motorola was somewhat better for longevity, but still quite a ways below Rauland (Zenith) at that time.

In the case of the Saticon camera tubes in the 1980's tube-type HDTV cameras, the tube was rated for only 600 hours before they might begin to go bad - and it was recommended to run them for a few hours every 6 months or less - no long periods of unpowered storage. Again, I think this was to eliminate effects of residual gas. At the Zenith lab, we preemptively retubed our camera at a cost of $85,000 after about 800 hours. The old tubes were kept on the shelf as backups in case of a catastrophic failure, but of course they didn't get fired up after that, so may have gone bad anyway.

andy · #9 02-21-2006, 10:55 PM

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rca2000 · #10 02-22-2006, 03:45 AM

[Bottom line: A CRT new in the box, with excellent vacuum, should stay as new forever. But one with poor seals (15GP22, and any metal/glass combination), or any CRT with less than excellent vacuum (Sony from the 80s/90s, Mitsubishi projection from 90s, etc) will deteriorate no matter what, but can be kept alive longer if the filaments are warm all the time.

Charles[/QUOTE]

You are SO right on the Mitsubishi CRT's in their Big Screens. I worked on one today, a 97 model or such,and the tubes are Shit. I mean, they work, but they have that "soft" look, that mits tubes are known for. whereas, my '94 RCA BS with hitachi tubes looks better than some new sets. I am sure that probably 85-90% of the tubes life is still there. This is NOT the exception, rahter the rule, where those RCA sets (and hitachis too) from the late '80's to late '90's are concerned. The tubes seem to be nearly bulletproof, and last and last and last. I have seen only a handful of bad ones, out of many hundreds of them I have worked on, compared to many bad mits. tubes. To me that is SAD, because Mits. was SUPPOSED to be superior to Thomson(RCA) but the tubes (and caps on the boards) sure arent!

I figure, that the Hitachi tubes must have well evaporated cathodes with a lot of VERY pure material, and a very good vacuum, whereas the MIts. tubes probably have a softer vacuum, with less material evaporated on it, and less pue too. (RCA direct-view tubes from the last 20 years or so are similar in this regard,of very high quality and durability, only recently have they switched to a "crappy" tube, to cut cost.)

bgadow · #11 02-22-2006, 11:27 AM

In regards to Admiral, I read a history of the company which gave a little detail about their attempt at crt manufacturing. The story said that they were never able to build a good color crt despite extensive efforts. When they finally gave up & tore the equipment down they found that the water purification system had been, apparently, sabotaged as scraps of metal were found in the tank. I notice that Admiral had unusually long warranties on their picture tubes for awhile & I wonder how that played into this.

I have one 10BP4 which tested very weak so I rejuvenated it. It then looked pretty good. The next time I used the set, a year later, I thought the hv had quit as there was no light on the screen. The crt is dead again. I know that it has had a full life-it has what look like ion burns, which couldn't help the gas situation.

Something I have noticed: as a rule Sylvania crts are not that great. I had a 15" Sears from the early 50s with an open filament Sylvania; the 21FP4 (?) in the Emerson I was just working on is pretty weak, and the Andrea I have has a Sylvania that tests okay but looks soft. I have also seen a few of their color sets that looked used up ahead of their time.

domfjbrown · #12 02-23-2006, 07:40 AM

Quote:

Originally Posted by rca2000

You are SO right on the Mitsubishi CRT's in their Big Screens. I worked on one today, a 97 model or such,and the tubes are Shit. I mean, they work, but they have that "soft" look, that mits tubes are known for.

I don't think this follows for British Mitsu sets; my parents' 1994 21incher still looks as bright and sharp today as it did then; it actually has better dynamic range than many Sony Trinitrons, although the "football" nature of the faceplate isn't as nice as the older Sony cilyndrical one...

andy · #13 02-23-2006, 02:45 PM

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JCFitz · #14 02-23-2006, 07:48 PM

Quote:You are SO right on the Mitsubishi CRT's in their Big Screens. I worked on one today, a 97 model or such,and the tubes are Shit. I mean, they work, but they have that "soft" look, that mits tubes are known for. whereas, my '94 RCA BS with hitachi tubes looks better than some new sets. I am sure that probably 85-90% of the tubes life is still there. This is NOT the exception, rahter the rule, where those RCA sets (and hitachis too) from the late '80's to late '90's are concerned. The tubes seem to be nearly bulletproof, and last and last and last. I have seen only a handful of bad ones, out of many hundreds of them I have worked on, compared to many bad mits. tubes. To me that is SAD, because Mits. was SUPPOSED to be superior to Thomson(RCA) but the tubes (and caps on the boards) sure arent! :Quote

Mitsubishi seemed to go downhill in the 90's.I've replaced many a cap in both projection and directview sets.But I haven't seen that many bad CRTs in Mitsubishi like you have.I've seen some 80's sets that the CRTs were shot or going downhill in recent years.The worse problem they have now is leaking coolant fluid.This happens on Mitsubishis from 96' or newer.It leaks on the circuit boards and shorts them out.The worse is the newer sets from 1999 on up with double sided signal boards and surface mount ics and a lot of boards are NLA.The fluid damages the feedthroughs and the open ones must be traced out and jumpered.The older ones from the 80s were better apart from the yoke failures on the 1985 models.I saw one with the fold out mirror from 1981 being used everyday and still going a couple years back.My mom has a 1987 60" Mitsbishi projo still going strong.Gets a lot of hours use every day.It even has the original convergence STKs.I dunno why they'e still working.They never last this long.One of these days I guess I'll get a phone call about the convergence.Only had the HV bleeder block go out in 2000.I've seen tubes die when they sat for long periods of time.I had a GE 25" console from the late 70s(the one with the large neck inline tube)In the early 90s it was getting weak on me.Had to keep the contrast down to prevent smearing and blooming and it didn't track very well.Rather than taking it to the auction to get rid of it right away(when you could get somethiing for a console even if it didn't have perfect color.I took my weak picture tube but still playing tvs there.I took the good ones to the flea market.)I sat it in the garage for a month.When I plugged it in at the auction the emission had fell off so bad from sitting you could hardly see the picture.I had to crank the screens and drives just to get a passably bright mostly blue picture.Green and red were done for.It had green and red when I unplugged it in the house.

domfjbrown · #15 02-24-2006, 04:27 AM

Quote:

Originally Posted by andy

I think he was talking about Mitsubishi projection CRTs. I've never had any problems with their direct view CRTs.

Aha - projection tellies. Forgive me for being blunt but, err, yuk! I've never seen a projection telly I can live with - as with older-format LCD screens, if you have nystagmus, all you see with one of those is fading, blur, and blooming...

I'd much rather have a small direct view telly than a large projection one