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Old 16th Feb 2019, 8:23 pm   #81
Maarten
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Default Re: Types of CRT used in colour TV's.

At some point in time, Videocolor used a system similar to the one that Philips used instead of a traditional hand-adjustable multipole unit. It consisted of a permalloy strip wrapped around the neck with yellow tape and magnetised in the factory.
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Old 17th Feb 2019, 12:00 am   #82
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Default Re: Types of CRT used in colour TV's.

Quote:
Originally Posted by Philips210 View Post
When the electrons are accelerated and strike the phosphors at the back of the faceplate, X-rays can be produced but the leaded glass will mostly absorb these. Increasing the final anode's potential (EHT voltage) above 25kV increases the risk of forward radiation from the front of the tube. I think it needs to be over 30kV for anything significant to happen.
Many early colour TVs that used the GY501/PD500 EHT valves had to employ screening around these to shield against X-rays. The PD500 shunt stabiliser valve being the main concern, though the EHT rectifier, GY501, could also produce X-rays is there was a heavy load on its cathode.


Setting up the PIL CRTs is about the same for any modern 90 or 110 degree CRT. This is a factory setting with a bonded yoke. Many 90 degree PIL CRTs have a multipole unit on the neck to set the purity and static convergence.

PIL S4 CRTs both 90 and 110 degree have a similar type of multipole unit. On the Philips 30AX and 45AX systems there's no external multipole unit, its preset internally during manufacture.
The really clever part of PIL CRTs is the yoke technology, in particular the way the line and field scan coils are wound to minimise raster distortion.

There weren't huge numbers of 110 degree deltas as the PIL CRT was coming on stream so I guess you could say 110 degree PILs were more common than 110 degree deltas.
Hi,

Think I might've got some things muddled up a little bit then. What is the average EHT voltage? I assume this varies slightly between sets' tubes and circuitry. I'm not as familiar with valve sets, but I assume the valves work in these sets work in the same way as valve amplifiers?

Are the multipole units the little knobs? My Hitachi has 7 of these on the PCB on the end of the tube

It makes sense that the two new technology's were combined to make one better tube, smaller and more convenient.

Thanks
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Old 17th Feb 2019, 1:03 am   #83
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Default Re: Types of CRT used in colour TV's.

Quote:
Originally Posted by slidertogrid View Post
Thorn had a habit of mounting the delta gun tubes upside down to help mask the lack of raster correction the problem with this was that the nicotine infused condensation tended to run down to the anode cap and cause arcing , I lot of houses had no central heating back then so the sets were turned on for an evenings viewing in a cold un heated front room .
Hi

I used to have this problem occasionally on some 3000s and 8500s. A lot of the time it was due to high humidity and the then standard PVC EHT cap used to track and become conductive. I think a lot of the Japanese EHT caps were silicone and provide far superior sealing and insulation. I don't ever recall one failing. When silicone EHT caps became available as a spare part, I used to replace the old PVC caps if arcing and corona discharge was a problem.

Regards,
Symon
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Old 17th Feb 2019, 1:05 am   #84
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Default Re: Types of CRT used in colour TV's.

EHT varies by set and tube type. Between 22 and 28 kV for colour sets normally, but in some large flat screen sets it can be as high as 29 to 33 kV. I suspect no dangerous level of X-rays is generated due to the large distance the electrons have to travel and the large area they're spread out over. Whatever X-rays are still generated, are caught in the leaded glass. In the PD500 ballast tube that was mentioned above, a very concentrated beam of electrons under high current is generated when the picture is black, and some X-rays are defnitely generated.

The multipole unit as mostly seen on Japanese and US designed tubes (PIL and other inline tubes) consists of some (often 3 pairs) weakly magnetized discs with tabs on them so you can turn them to influence how the 3 beams leave the cannon. B/W tubes can have similar discs on the small end of the deflection coil for adjusting geometry. 20AX tubes actually used coils for the 4-pole part of the multipole unit since dynamic correction was needed (this is how I remember, I haven't checked the brochure that was helpfully linked above, please doublecheck) and the other multipoles were integrated into the deflection unit instead of on a separate neck assembly. In 30AX and later tubes, the multipole unit is internal to the tube and is magnetized for adjustment during the production process. In some videocolor tubes this units is external but als magnetized during the production process so not adjustable in the field.

EDIT about the moisture problem: I know of an old time serviceman who would put bags of sugar in the set and exchange them each service. I wonder for how long they actually absorbed moisture.
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Old 17th Feb 2019, 1:24 am   #85
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Default Re: Types of CRT used in colour TV's.

Quote:
Originally Posted by InsertNameHere View Post
Think I might've got some things muddled up a little bit then. What is the average EHT voltage? I assume this varies slightly between sets' tubes and circuitry. I'm not as familiar with valve sets, but I assume the valves work in these sets work in the same way as valve amplifiers?

Are the multipole units the little knobs? My Hitachi has 7 of these on the PCB on the end of the tube

It makes sense that the two new technology's were combined to make one better tube, smaller and more convenient.
Hi.

The EHT is typically 25kV in large screen colour TVs. Some of the smaller screen sets will have an EHT of about 20kV. I think some very large screen sets can have an EHT of around 27kV but I'm fairly sure this will be the upper limit.
For the operation of the valve line output stage, I'd recommend having a read through some TV circuit text books. There's also a useful description here https://www.vintage-radio.net/forum/...ad.php?t=20778
It's well worth reading through the TELEVISION magazines that have a wealth of information.

The mulipole unit is that set of ring magnets fitted to the CRT neck.

Regards,
Symon
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Old 17th Feb 2019, 8:22 pm   #86
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Default Re: Types of CRT used in colour TV's.

Quote:
Originally Posted by Maarten View Post
EHT varies by set and tube type. Between 22 and 28 kV for colour sets normally, but in some large flat screen sets it can be as high as 29 to 33 kV.

Thanks for pointing that out Maarten, I wasn't aware of the EHT being in the region of 29 to 33kV for large flat CRTs. The highest I recalled back in my repair days was about 27kV on some 28" tubes.
For such a high EHT, insulation qualities of the LOPT would need to be that much better than normal. Would a normal diode split type LOPT have been used or would a separate LOPT and EHT multiplier have been employed instead? Maybe the latter to keep the stresses on the LOPT within reasonable limits.


I had to chuckle reading about the bags of sugar being used as a cheap dehumidifier, very good

Regards
Symon.
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Old 17th Feb 2019, 11:07 pm   #87
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Default Re: Types of CRT used in colour TV's.

Hi Aaron,
Here are some pictures of the scan/correction assembly used on delta gun CRT's. These were taken of my Pye CT205 which is dated Nov 1973.

Picture No 1 shows the size of the assembly mounted to the tube neck. Picture No 2 is the rear view. The three knobs mounted to the little PCBs are the static convergence controls. The lower right one is for the red and moves the whole of the red raster diagonally across the screen. The lower left one is to move the green raster diagonally but in the opposite direction to the red.

The one at the top is the blue and moves the blue raster vertically up and down.
These controls are used to get the three rasters to overlap (converge) in the centre area of the screen.
Nearest the pins at the end of the tube is the ' blue lateral' unit. This shifts the blue raster horizontally side to side.
Just behind that are the brown ring magnets which shift the whole picture about on the screen.

Picture No3 shows the dynamic convergence board with all its adjustments and the order in which they should be done.

If you look closely at the first picture, you can see a wing nut about half way along the yoke. These's one on the opposite side as well and slackening these allows the scan coils to be moved forward and back within the whole plastic yoke assembly. This allows the 'purity' to be adjusted. This ensures that the correct coloured beams hit the correct phosphors.

ALL the above adjustments interact so you have to go through the whole process multiple times to get a good result!

So you can see how complex the set up is both to manufacture and to adjust. The PIL tube made this whole process much simpler.

The last two pictures show the whole chassis. You will see it still uses some valves (7 in fact). These sets were pretty reliable from an electronic point of view, but suffered from multiple PCB burn ups due to the heat and high voltages generated by the valves.

If I can coax some life out of the set, I'll try and show you what effect the controls have on the picture convergence.

Hope that's of some interest

All the best
Nick
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Old 17th Feb 2019, 11:22 pm   #88
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Default Re: Types of CRT used in colour TV's.

And as promised, a couple of the my Thorn 2000 chassis. This was the first all transistor colour TV and was produced in 1967. It's ludicrously complicated and pushed the transistors of the day well beyond their limits. Special quality transistors had to be designed for it. Just to make it even harder, it was a dual standard set so it would receive black & white 405 line transmissions and also the new BBC2 channel on 625 line UHF. There was very little colour TV broadcast at that time.

The first picture shows the convergence board and the second the whole chassis. The set uses no less that three line output transformers!! It took two men half a day to deliver one to a customer and set it up correctly!!

You can now see why Forum members advised you not to get a delta tube set from the '70's! They are not for the faint hearted!

More information about this particular set can be found here: https://www.vintage-radio.net/forum/...d.php?t=135994

Cheers
Nick
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Old 17th Feb 2019, 11:22 pm   #89
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Default Re: Types of CRT used in colour TV's.

Hi.

Regarding the early colour CRTs such as the 25" A63 120X, I always thought the width to height dimensiions of this CRT appeared to look more "square" than the later "rectangular" looking A66 120X.
The aspect ratio of the latter is 4:3 approximately. Having found some mechanical specs on both CRTs (info attached) my thoughts were confirmed when looking at the measurements of the A63 120X. This CRT has an aspect ratio of about 5:4. I refered to the useful screen horizontal and vertical dimensions in the attached pics.

Were all the pre "rectangular" CRTs 5:4 including the 19" Mullard "Panorama" as used in the GEC 2028?
I suppose it would have been the same for the mono CRTs as well such as the 19" and 23" sizes ie 5:4. The later 20" and 24" would have been 4:3. Anyone else noticed this?

Regards,
Symon.
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Old 17th Feb 2019, 11:29 pm   #90
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Default Re: Types of CRT used in colour TV's.

The original CRT used in the RCA CT-100 chassis was the 15GP22. These were in extensive use in America in 1954. Grob's television book describes them well, along with the "single gun color kinescope" (which appears to have been developed by RCA at about the same time as the 15GP22) and looks pretty well exactly like a Sony Trinitron CRT. I think the problem was at the time, for RCA at least, the single gun color CRT required too much additional support circuitry, making it less economic. But the Japanese didn't let that stand in their way later.

The ETF has been doing some encouraging work attempting to rebuild the 15GP22, it is a very difficult task:

http://www.earlytelevision.org/15gp2...ld_report.html
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Old 17th Feb 2019, 11:43 pm   #91
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Default Re: Types of CRT used in colour TV's.

Ni Nick.

The Pye hybrid colour sets bring back good memories for me and it's great to see some pics again. I used to pick these up for £5 each from a friendly TV repair shop when I was about 16. I think in reality they were pleased to unload them but I learnt a huge amount working on these sets. True they're not to everyone's taste but when set up correctly gave good results and were very simple to repair. The earlier metal timebase was more reliable than the 697's PCB type power/line timebase. It never seemed a good idea having the PL509/PY500A line output valves on a PCB, just as with the heat problems with the valves on the CDA panel.
Looking at the convergence board in your pic reminded me of a pot that used to play up regarding N/S raster correction I think it was RV41 from memory but that was a long time back so I may be mistaken.

Your BRC 2000 looks great as well. I wish that I saved the one I had back in the early 1980s. My only gripe with BRC/Thorn was their CRTs. THe Mazda CRTs could display an excellent picture possibly better than some Mullards but the Mazdas just didn't last very well. I see the 2000's CRT is mounted the "right" way up not like on the 3000s and 8500s. Does your 2000 have the transductor fitted for N/S raster correction?

Regards
Symon.
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Old 18th Feb 2019, 12:10 am   #92
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Default Re: Types of CRT used in colour TV's.

Quote:
Originally Posted by Philips210 View Post
The Pye hybrid colour sets bring back good memories for me and it's great to see some pics again. I used to pick these up for £5 each from a friendly TV repair shop when I was about 16. I think in reality they were pleased to unload them but I learnt a huge amount working on these sets.
Hi Symon,
The CT205 was the first colour TV I got to grips with as a teenager. As it's got a n entirely discrete decoder, it was a great set to learn how a PAL decoder actually worked. I used it for a while and then stripped out the chassis and replaced it for a G8!- it worked a treat!
I got the current one at RWB about 15 years ago for £1.00 in the auction! It's in good condition with only minor print damage on the LTB and no toasting of the CDA board. As with all my projects it's not fully finished....

Quote:
Your BRC 2000 looks great as well. I wish that I saved the one I had back in the early 1980s. My only gripe with BRC/Thorn was their CRTs. THe Mazda CRTs could display an excellent picture possibly better than some Mullards but the Mazdas just didn't last very well. I see the 2000's CRT is mounted the "right" way up not like on the 3000s and 8500s. Does your 2000 have the transductor fitted for N/S raster correction?
The link to the above thread shows that this actually was the set I had in the early '80's! It's survived entirely by accident! You are right about the CRT being the right way up-I thought they mounted them upside down to disguise the lack of pincusion correction? Although how that would help, I don't know! I didn't think any production sets had the transductor fitted, although mine has the holes for it.

It's riddled with Callins caps so will need some TLC, but I daren't start on it before I've finished at least some of the current projects!

Cheers
Nick
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Old 18th Feb 2019, 12:48 am   #93
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Default Re: Types of CRT used in colour TV's.

Hi,

Thank you for those photos and the explanation, I really appreciate it.

That looks very, VERY confusing! I would definitely like to be able to work on sets like this at some point, but not for a while...

It sounds quite complicated, but after a while I suppose you get used to it, and become familiar.

Could the valves not be replaced with suitable transistors to cure the heat issues?

I'd love to see what they do if you do get any life out of it!

Reply to your follow up Thorn 2000 Chassis post -

That looks slightly less confusing (Tidier looking) to me, but never the less, still confusing! (No where near as confusing as the prototype! attached)

Were there any 405 line colour transmissions? I know colour didn't catch on until roughly the same time as 625 line.

The convergence board doesn't look any less confusing, if not more confusing due to the guide on the PYE.

I can see why it took them time to set it up, I'd imagine that happened up and down the country!

As you can say, I can see why members didn't recommend me getting a DG for a starter, and I have to say, I really thank you all for that!

I'll have a read on the thread you linked, these sets interest me quite a bit.

Thanks
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Old 18th Feb 2019, 12:56 am   #94
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Default Re: Types of CRT used in colour TV's.

Quote:
Originally Posted by Argus25 View Post
The original CRT used in the RCA CT-100 chassis was the 15GP22. These were in extensive use in America in 1954. Grob's television book describes them well, along with the "single gun color kinescope" (which appears to have been developed by RCA at about the same time as the 15GP22) and looks pretty well exactly like a Sony Trinitron CRT. I think the problem was at the time, for RCA at least, the single gun color CRT required too much additional support circuitry, making it less economic. But the Japanese didn't let that stand in their way later.

The ETF has been doing some encouraging work attempting to rebuild the 15GP22, it is a very difficult task:

http://www.earlytelevision.org/15gp2...ld_report.html
I've seen a set dating from 1954 with a tube that wasn't as large as this, we're there many other tubes?

As you say sony used the idea later on, but isn't 1968 when the trinitron entered the market? If so, in that 14 year gap, i'd have thought some decent advances in technology would've helped Sony? I could be wrong

Thanks
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Old 18th Feb 2019, 2:36 am   #95
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Default Re: Types of CRT used in colour TV's.

As I wrote, Sony had been experimenting for quite some time by then.

I'm not sure the RCA definition of single gun was the same as the one Sony used, so not sure if they used the same technology and if advances helped Sony (if by single gun they meant single cathode as well: Sony didn't quite get that to work either, that's why Trinitron came into existence, stuffing 3 cathodes in a structure that was otherwise like a single gun).
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Old 18th Feb 2019, 2:49 am   #96
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Default Re: Types of CRT used in colour TV's.

I think Sony had been experimenting in the late 50s, early 60s - this could be for another design, although.

This is probably a really simple question, but is the cathode what emits the electrons?

Technically, Trinitron is a three gunned set, but was sold as a single gun, whereas RCA was really a single gun set?

Thanks
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Old 18th Feb 2019, 3:59 am   #97
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Default Re: Types of CRT used in colour TV's.

The cathode is indeed the part that's heated to emit electrons.

Technically, a Trinitron cannot really be called a three gunned tube as they have only one of most gun parts but it's also not really a single gun as there are three cathodes. For marketing purposes, Sony always went with the single gun definition. It's a bit like calling a LCD TV with LED backlight, a LED TV like most manufacturers do. Not incorrect but also not fully accurate and makes the technology sound properly advanced.

I'm not sure about the gun construction that RCA used before they went with the triple gun shadow mask system they licensed to most of the industry.

I wanted to write: the only tubes you can be sure have a real single gun, are b/w tubes but then I thought that isn't quite true either. Philips made instrument tubes (megapixel tubes for medical instruments) with b/w phosphor but everything else constructed like the inline colour equivalent including the gun. I'm not sure whther they used all three beams. I think they did, but how and why?

Last edited by Maarten; 18th Feb 2019 at 4:08 am.
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Old 18th Feb 2019, 4:32 am   #98
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Default Re: Types of CRT used in colour TV's.

That’s cleared some stuff up then!

That’s marketing for you though, defining only the best parts of the product, or what makes it look better, just as Sony did really. It’s a clever trick, in a way.

B/W sets would be more likely to use single guns, presumably, most likely from the 1950s and before.

Thanks
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Old 18th Feb 2019, 11:40 am   #99
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Default Re: Types of CRT used in colour TV's.

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Originally Posted by InsertNameHere View Post
Hi,
Could the valves not be replaced with suitable transistors to cure the heat issues?

There were certainly attempts to do this; Ledco sold a replacement CDA panel for the Pye hybrid chassis and a plug-in replacement for an expensive valve type as shown in posts 32 and 33 of this thread.

https://vintage-radio.net/forum/show...=129126&page=2
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Old 18th Feb 2019, 3:33 pm   #100
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Default Re: Types of CRT used in colour TV's.

were these decent? I’d imagine for £8 back in the 70s/80s, as the OP of them photos said, thats fairly expensive, so I’d imagine they were somewhat decent?

Thanks
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