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CRT longevity in different chassis.

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Boingy
(@boingy)
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Hello all,

I seem to recall that certain chassis seemed to look after their tubes better than others. For instance, ITT CVC9 tubes seemed to last longer than Philips G8 ones. If my memory serves me correctly, didn't the 22" versions of these chassis use A56-120X tubes?

The CVC9 was a hybrid set, with a valve line O/P stage. I think the tube heaters were part of the heater chain for the other valves.

The 26" ITT we had indoors lasted ages with a great picture. The death knell for that set was the LOPT was no longer available. The tube was transplanted into a G8, but was flat within a year, as I recall. 

From my days in the business, the best tube/chassis were the Mitsubishi Blue Diamond tubes fitted in the CT2017 and CT2217. We had loads on rental and usually we'd only see them in for dry joints, or a blown HT fuse, which was of the fast blow type. Never recalled seeing a duff tube on them. When the business closed, we let the customers keep those tellies for free. Those tellies seemed to be the exception, rather than the rule, though.

So, does anyone agree that hybrids generally looked after their tubes better than the fully transistorised chassis?

All the best,

Tony

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Topic starter Posted : 05/04/2018 1:18 am
Nuvistor
(@nuvistor)
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Out of the few makes we dealt with and over the 13 years I was fixing CTV’s, I don’t think so. The earlier sets had a mains transformer fed heater supply, 6.3v 0.9amps I think ?

Some later sets that were transistorised have quick heat CRT’s , I found these poor but I don’t think it was the fault of the set design, more CRT design.

I found the CRT’s from early early 70’s, A56-120X type lasted on average just under 4 years and got them replaced under extended warranty.

I did not have a large sample to judge by, one of the big rental outfits would have much better data.

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Posted : 05/04/2018 8:14 am
crustytv
(@crustytv)
Vrat Founder Admin

Hi Tony,

An interesting post and question, look forward to hearing what the other folks opinions regard this are. I can only speak from what I have in the collection and it would seem all my hybrids bar one (22" Decca CTv22C, though it responded to a tickle) have excellent tubes. Must admit I hadn't even thought of it before you mentioned it. Come to think of it the ones that were low to flat were in all transistor sets, coincidence or the reason you put forward, I cannot say as I've no trade experience to call upon.

I know in the 3K sets there was an option to shift the CRT heaters to a higher voltage tag on the TX to squeeze the last ounce of emission from the tubes, but in the three cases I had, this had not been done. Some say that unscrupulous engineers would do this but perhpas it was more likely the customer who wouldn't fork out for a replacement and wanted every last ounce from the tube. Perhaps the large rental companies adopted that practice to get the max out of every set on rental.

Another engineer on here @jayceebee also mentioned the Mitsi Blue Diamond CRT was unmatched in terms of quality picture, I've never seen one. I seem to recall he said it was fitted to Thorn 9800 chassis'.

As I say, look forward to reading other folks thoughts  ? 

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Posted : 05/04/2018 8:30 am
Nuvistor
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I didn’t have a CRT rejuvenator, a low emission CRT was replaced or the occasional BW one was boosted with a TX. The Hitachi CRT in my own CNP192 lasted around 10 years of daily use and then the TV was consigned to the role of a second set.

I didn’t have much success with the Mullard quick heat type CRT’s, was there a modification to use a standard type in some sets? The directly heated Hitachi CRT’s were dreadful from my experience but you needed to be careful, the heater chokes in the CRT base PCB went dry joint and that looked the same as a low emmision gun. They stopped using them so perhaps my experience was not an isolated one.

I never, as far as I can remember replaced a a Toshiba CRT in a Toshiba TV but replaced many in U.K. sets, RBM and Pye come to mind, but as always it’s a long time ago to remember accurately.

Qualifying that last statement, the CRT’s were made in Japan, I believe they were Toshiba, some were labelled as such but some had a Mullard label “ made in Japan”

 

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Posted : 05/04/2018 9:31 am
malcscott
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The first generation Mullard A56-120x (green label) lasted well. The red label ones made in Durham were the best. The yellow label ones made in Japan were very poor. The was also some white label ones (USA) not very good. Mullard produced a batch of quick heat A56-120X which Rediffusion used in their refurbished RBM A823 chassis (RT529/22). I have never seen a crt with a faster warm up time. A good picture appeared within 2 seconds and the degause cycle was visible, Malc.

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Posted : 05/04/2018 10:37 am
Cathovisor
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Why should the set being a hybrid make one iota of difference? Most of the hybrid sets used transistor RGB drive to the CRT (with one or two notable exceptions, usually those sets with CDA drive) anyway and all had a mains transformer for the CRT heaters, because they drew 0.9A so unless they were terminating three 0.3A chains in parallel I can't see how you'd put them in a series heater chain.

Anecdote ≠ Evidence.

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Posted : 05/04/2018 2:35 pm
Doz
 Doz
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What about the Philips K30 ? It ate A56-540X for breakfast ... except the basic "1234" model which always seemed to have a bramah of a tube in it!

... and those awful amstrad CTV 2200's ... always has a brilliant A56-540X , perhaps they never lasted long enough to wear the things out! 

All green label mullards...

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Posted : 05/04/2018 2:43 pm
Nuvistor
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As long as the CRT is operated within its normal parameters, the lifetime must be attributable to the quality in its design and manufacture.

I don’t recall the sets I worked on using the CRT outside those specifications and always put poor CRT life down to the quality of the CRT. 

But I have been wrong on more occasions than I like recall. ? 

 

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Posted : 05/04/2018 4:20 pm
PYE625
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I guess another factor that could play a part is how much beam current was demanded during the set's use by a customer. If contrast and brightness were always set on the high side, would this reduce the life?

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Posted : 05/04/2018 6:18 pm
malcscott
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The high rate of crt failure in the Philips A10 chassis was due to the crt cathode current setting to high.

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Posted : 05/04/2018 6:42 pm
Nuvistor
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Posted by: malcscott

The high rate of crt failure in the Philips A10 chassis was due to the crt cathode current setting to high.

Was that a design issue or a setup of the internal controls issue, I have no experience of the A10 chsssis?

 

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Posted : 05/04/2018 8:12 pm
malcscott
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The cathode current is adjusted in the factory settings. 0 - 10. Many sets left the factory set at 9 or even 10. Normal setting is 3 -4 max. When the painter ic or crt was replaced i always set them at 3. When set at 9 the tube was very much over run.

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Posted : 05/04/2018 8:19 pm
Nuvistor
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Posted by: PYE625

I guess another factor that could play a part is how much beam current was demanded during the set's use by a customer. If contrast and brightness were always set on the high side, would this reduce the life?

Certainly wouldn’t help, only so much cathode material. 

Another problem we had that I am not sure whether to smile or just feel quite sad. The last TV company I worked at did a lot of rentals with slotmeters on tbe tv’s, perhaps one of the reasons I wanted to leave.

The boss, it was a very small company, would go round emptying the meters, very often there was no one home but he could see the TV through the window switched on. He would call round later and ask why, the reply was they were using the meter to save up, the more they had the TV on, the more rebate would be paid back in overpayment.

Must be some logic there but lost on me.

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Posted : 05/04/2018 8:19 pm
Nuvistor
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Thanks Malc  for the Philips A10 information.

 

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Posted : 05/04/2018 8:21 pm
malcscott
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The Rediffusion MK1 chassis used a mix of Mullard, Mazda and Sylvania tubes. The Belgium made Sylvania ones were very good.

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Posted : 05/04/2018 8:55 pm
abctelevision
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Posted by: Doz

What about the Philips K30 ? It ate A56-540X for breakfast ... except the basic "1234" model which always seemed to have a bramah of a tube in it!

... and those awful amstrad CTV 2200's ... always has a brilliant A56-540X , perhaps they never lasted long enough to wear the things out! 

All green label mullards...

I agree with you on the PhillipsK30 I had experience with the 26 inch tube.

I bought one second hand many years ago, it was cheap has it had a flat tube. I bought a regunned tube for it, and paid extra for a 6 month guarantee. After around 4 months I thought the picture was not looking good so I took the set back to the place that regunned tubes. As soon as he saw the set he said not one of those and gave me back my money. He said if he had known it was for a K30 he would not have given a 6 month guarantee. He normally would give 3 months.. He went on to say that the problem had something to do with the heaters getting too much power?

Valve or hybrid sets the heater voltage is pure a.c and easy to calculated. For transistor sets the heaters are powered differently from sources that may have given an average value of 6.3V but the waveform may be anything but sinusoidal which could result in early CRT demise.

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Posted : 05/04/2018 9:01 pm
Jayceebee
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Posted by: Chris

Another engineer on here @jayceebee also mentioned the Mitsi Blue Diamond CRT was unmatched in terms of quality picture, I've never seen one. I seem to recall he said it was fitted to Thorn 9800 chassis'.

The 9800 chassis models were fitted with an RCA(?) sourced Black Matrix delta CRTs not Blue Diamonds I'm afraid Chris. The chassis was much maligned because of it's cost cutting inertia start up PSU arrangement which dispensed with the costly mains transformer for the low voltage and heater supplies, all the ones I saw gave a much better picture compared to the 8800 chassis after the mod for PSU flutter had been carried out. I only ever saw 22" models though, the 26" version apparently had a fairly short life span.

Totally agree with Doz about the early 30AX CRTs, the first metal chassis versions of the TX10 had very short lives. The ones fitted in the later plastic TX10 seemed to last much longer and there was no difference in the CRT drive circuitry, the changes were to the line/field drive and field output stages only. Even worse although only used in the early very TX10 was the RCA sourced A56-701x PIL S4, these were lacklustre even when new and also had a short life.

John.

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Posted : 05/04/2018 10:33 pm
crustytv
(@crustytv)
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Posted by: Jayceebee
The 9800 chassis models were fitted with an RCA(?) sourced Black Matrix delta CRTs not Blue Diamonds I'm afraid Chris.

John.

Oh dear! my brain fade again  ? 

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Posted : 05/04/2018 10:40 pm
Boingy
(@boingy)
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Thanks for the replies everyone.

To be fair, I've forgotten far more than I remember, so the technical details of many sets have faded from the old organic database in my head. The need for the intricacies has moved over to white goods nowadays for me. It's nice to get calls from other engineers in my team, with their electrical or electronic queries. It amazes me how many still think of electronics as some form of black magic!

As Cathovisor said, my anecdotes are not evidence, so apologies if I came over as such, as that was not my intention.

I can certainly remember having to take the backs of TVs in certain ex-rental warehouses to check if the heater resistors (or chokes) were shorted out to get a brighter picture. Think of all the line rate spikes on the poor old heaters, if the heaters were fed from the LOPT, which was sort of the point about fully transistorised sets. If the CRT's heaters were designed to be fed by 50Hz AC from a mains transformer, then wouldn't having the same CRT being fed by line pulses be changing the operating parameters?

Of course, there were many tube heaters designed to be fed off the LOPT, but how many of these tubes lasted? My gut feeling is there wasn't that many, especially when tube necks got thinner. 

It may be that many hybrids were simply fitted with better quality tubes. It's only academic now obviously, but it was nice to start of a conversation.

All the best,

Tony

 

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Topic starter Posted : 06/04/2018 12:32 am
Cathovisor
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Shorting out resistors and chokes was really the last resort in some cases - but what it did to the drive to the CRT heaters is anyone's guess! True RMS voltmeters were very expensive and I'd wager that those tubes fed from a LOPT overwind were getting overrun, especially when chokes were being shorted out.

It's sad really that the issue of CRT cathode degradation was solved just as CRTs went out of fashion - the 'dispenser cathode'. Some of the very last CRT TV sets used this type of construction.

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Posted : 06/04/2018 8:41 am
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