Types of CRT used in colour TV's.

[19Seventy7]

Thats him!

I havent known - and still dont know - many faults, but thats the first id ever seen of a cataract problem.

I suppose some respect is better than none at all.

[Maarten]

Originally Posted by InsertNameHere

I didn’t think it would, but i was just curious, i suppose thinking about it, it makes sense with delta guns having circles forming triangles (if that makes sense) and PIL having lines. I’d be fascinated to see if there was any simulation or anything of what a PIL set with a DG shadow masks’ picture would look, and vice versa.

Most computer monitor CRT's have their phosphors arranged in a delta like pattern to obtain a higher resolution.

[Maarten]

Originally Posted by InsertNameHere

I saw a video a few days ago of someone replacing the tube in an American RCA set, or a Zenith, and he removed the front glass protective panel to clean it and had to cut through adhesive. Is this the same thing or slightly different.

That's something entirely different. Since picture tubes are high vacuum with around a metric tonne of air pressure on the screen and a bit more on the back, they were prone to violent implosion when struck by a hard object or otherwise subjected to mechanical stress. To prevent pieces of glass being ejected across the room (and into the viewers body), a separate piece of safety glass was required. Sometimes this was a flat piece of glass placed at the front of the cabinet, but US tubes tended to have a curved plate bonded to the tube. That was probably what you saw. Some time in the early to mid 1960's, it was discovered that a violent implosion could be contained by pre-tensioning the picture tube by crimping a steel band around the edge where the front and the cone of the tube are bonded, and the industry changed almost overnight. That's why you don't see separate safety glass anymore.

[19Seventy7]

If delta is a higher resolution, why did CRTs become PIL, or is that just for monitors, which could be capable of a better resolution when the user is closer to the screen?

What sort of mechanical stress can implode them?

I've seen the flat safety glass before, (My Waltham W154 has one)

The safety glass on the TV was bonded to the CRT with adhesive, i can't remember if he was just changing it, cleaning it, or replacing the CRT itself. - it was a round, slightly domed piece of glass, to cover the round CRT.

I never realised that, i always thought they had safety glass - you learn something new everyday


Thanks

[Graham G3ZVT]

As has been said, we didn't, thankfully, have those tubes with the safety-glass glued to the face-plate.
We did have tubes described as "twin panel" tubes for a while, I think they were similar to a laminated windscreen.

Another technique was the Fenbridge guard and this was decidedly dodgy for us service staff.

We sat at the workbench on typical wooden bar-stools, the seat squab would be removed and the new CRT would be placed neck-down in the aperture.

The rimband and four mounting brackets would have previously been removed from the old CRT.

A new Fenbridge guard, which we simply called a "skin" or occasionally a "Cornea Guard" was obtained from stores.

I should add at this point that guarding your own corneas with goggles was recommended, but not particularly strictly enforced by management.

Ok, back to the bar-stool and CRT

You need only three tools, a 4BA nut-spinner, a 2kW fan heater, and, I kid you not, a largish ball-pain hammer.

You placed the skin on the screen, being careful to exclude any dirt or dust (impossible)
then you placed on the rimband and inserted the four mounting luggs at their approximate positions, then moderately tightened the band's long 4BA screw.

After that, the idea was to heat the skin to soften the plastic and then tap tap tap the lugs with the hammer to stretch the plastic so it conforms to the curvature of the screen, and you probably needed to tap the lugs sideways to line them up to the threaded studs in the cabinet. Then a final tighten up of the band and in with the tube.

Granada Langworthy Road, Seedley (Salford), Circa 1972.

[19Seventy7]

I think it's relatively lucky we didn't have the round tubes either, i know it's just opinion, but I find the semi circular sides a little ugly... I prefer the slightly rounded edges of our tubes - That's just my opinion

Were the Fenbridge guards like an "Aftermarket" addition, or were these applied to new sets too?

Never thought when talking about the repair of a CRT would the word "Hammer" be used, especially a "largish hammer!"

Were the guards effective, if they were made of stretchable plastic, i wouldn't have thought they'd be the best option.

On the topic of dirt, what is the best way to clean a CRT screen? There are a few specs on the glass - I read that to clean them had to be done in a certain way, im not sure if they have to be done in a certain way with certain equipment

Thanks

[ms660]

The Fenbridge guard was fitted from new, it was a PITA to replace or to re-fit over a replacement CRT...Inevitably they turned a bit yellowish with age....

….Had to fit a fair few back in the 1960's....'orrible things.

Lawrence.

[19Seventy7]

Oh okay.

I had a feeling it was put on the original CRT for some reason..

were they satisfactory when fitted or worse than original?

[ms660]

Enter Fenbridge in the forums search box.

Lawrence.

[19Seventy7]

Will do!

Thanks

[1100 man]

Originally Posted by InsertNameHere

If delta is a higher resolution, why did CRTs become PIL, or is that just for monitors, which could be capable of a better resolution when the user is closer to the screen?

Once the manufacturing was perfected, PIL tubes had huge advantages, especially for set makers. They could dispense with large & costly deflection/ correction yokes and all the circuitry needed to drive them. Setting up the set was made much simpler and quicker.

If you've never seen the set up for a delta tube, I'll take some pictures of my Thorn 2000 which will show you how big the yoke is and how many convergence controls there are!

What sort of mechanical stress can implode them?

A brick lobbed at the screen by a 15 year old youth would do it!! I grew up in a rural village and instead of driving the 20 miles to the tip, people just dumped TV's (and everything else) in ditches & gateways. Within days, there would be a sea of broken glass once the tube got stoved in.

In order for a CRT to work, it has to be pumped out (evacuated) to a near perfect vacuum when it's made. This means that atmospheric pressure (15 pounds per square inch) is trying to crush it. If the glass gets broken, all the air rushes in at once and the forces tear the glass structure apart sending glass flying everywhere.
That's why earlier tubes needed a safety glass in front to protect the user from flying glass (and to protect the tube from impact). Then some manufacturers adopted the bonded plastic screen guard detailed above.

Early CRT's were round screen as it's a 'stronger' shape to contain the forces. It took manufacturers a while to figure out how to make rectangular tubes strong enough. The Americans had colour TV quite a few years before we did. By the time we got it, rectangular tubes were being made.

All the best
Nick

[19Seventy7]

Oh it's not mechanical as in the set itself destroying it. It's a shame that they got smashed. There could've been some nice sets, but just "too old"

I just watched a slow-motion video of a CRT imploding, and now I realise JUST how important the safety glass is.

I suppose with a round CRT, everything is supporting itself, rectangular, not so much? Could be wrong.

I think Americans got colour in 1954 or around that time.

I did wonder if PIL sets took over as they were cheaper to produce than DG sets. Would the advantages mainly be setting up and adjustments?

And i'd love to see some photos of the Thorn, I've never seen a DG set up, not properly anyway because all of the boards are in the way!

Thanks

[Maarten]

Originally Posted by InsertNameHere

If delta is a higher resolution, why did CRTs become PIL, or is that just for monitors, which could be capable of a better resolution when the user is closer to the screen?

No need to have a much higher resolution than 576*768 for 625 line PAL (the shadow mask may have a somewhat higher resolution to prevent interference patterns and always give the impression of a sharp image). Also, Sony got away with relatively coarse aperture grilles, even in computer monitors, since they had a theoretically unlimited vertical resolution.

What sort of mechanical stress can implode them?

Since it already has to withstand thousand kilogram or more of force, it takes a lot of concentrated force to crack the glass. For example a hammer strike, a shotgun shot, but also stress within the glass (spontaneous or temperature related). Picture tubes are pretty safe but not indestructible and when they fail, they should fail as safely as possible, hence either the safety glass plate or the pretensioning.

[Maarten]

Originally Posted by 1100 man

Once the manufacturing was perfected, PIL tubes had huge advantages, especially for set makers. They could dispense with large & costly deflection/ correction yokes and all the circuitry needed to drive them. Setting up the set was made much simpler and quicker.

If you've never seen the set up for a delta tube, I'll take some pictures of my Thorn 2000 which will show you how big the yoke is and how many convergence controls there are!

Monitor tubes sporting a delta-like shadow mask, have a normal inline gun and the adjustments are not much more complicated than those in inline tubes. I think the delta pattern in this case was used to get more and smaller pixels in the same area.

[19Seventy7]

Originally Posted by Maarten

No need to have a much higher resolution than 576*768 for 625 line PAL (the shadow mask may have a somewhat higher resolution to prevent interference patterns and always give the impression of a sharp image). Also, Sony got away with relatively coarse aperture grilles, even in computer monitors, since they had a theoretically unlimited vertical resolution.

Since it already has to withstand thousand kilogram or more of force, it takes a lot of concentrated force to crack the glass. For example a hammer strike, a shotgun shot, but also stress within the glass (spontaneous or temperature related). Picture tubes are pretty safe but not indestructible and when they fail, they should fail as safely as possible, hence either the safety glass plate or the pretensioning.

Would the sony sets be in question the Trinitrons? I think that they have a special shadow mask, i'm not sure... if they do, not sure if the shadow mask design is used in any other sets, sony or not.

If they had almost unlimited vertical resolution, couldn't something similar be done for horizontal, making a very high resolution CRT?

What is the chance of the glass failing? Couldn't an extra measure be taken, and pretension the CRT and have the safety glass?

Thanks

[Maarten]

The chance of glass failing under normal circumstances is almost zero, so no additional measures need to be taken. The only real concern is that if it should fail, it fails as safely as possible.

Trinitron tubes use an aperture grille. While a shadow mask is a piece of sheet metal with etched holes, an aperture grille consists of wires under tension in a heavy steel frame. The wires are vertical, so they only limit the horizontal resolution. Compared to an etched mask, the grille is relatively coarse due to its heavy construction and the size of the wires, so Sony and later Mitsubishi, constantly struggled to keep up and it's an amazing feat that they kept up as long as they did, using what was initially an emergency solution to get a conventional variant on their originally planned more complicated colour tube to the market without paying license fees to RCA for using the shadow mask (which was probably their emergency plan C). A distinct advantage of the grille construction is that the area of the phosphor stripes that can be illuminated is larger than in a shadow mask system where the mask gets in the way.

I think it should be clear already, that you can't leave out the wires from the grille (there would be nothing left) to obtain an unlimited resolution in both directions. The best way to obtain a resolution as large as possible using conventional means would be a shadow mask with a cleverly designed dot pattern, since that gives the best compromise between horizontal and vertical resolution.

[19Seventy7]

That's good to know

That makes sense about the wires, so theoretically, if the wires were horizontal, there would be a better horizontal resolution?

Did the Trinitron not run from the late 50s/early 60s to the 2000s, until the demise of CRT production, and as you say about keeping up, in the Trintrons first year, every set sold lost the company money.

[Maarten]

Trinitron, being an unplanned plan B, was actually late to the market, I think in 1968. Plan A was a beam index tube using a layout vaguely similar to what was to become the more conventional Trinitron design (the 3 cathode single lens gun, the grille, the cylindrical screen and the H-STAT setting were modified remains of the original attempts). They coudn't get it to work decentlly even with years of work and must have pulled some all-nighters or even all-monthers in the end to convert the beam index design into Trinitron in time to not miss their share of the booming colour market while still retaining face and not having to pay license fees to RCA. The kludge payed out in the end, as they have retained over the years a very loyal customer base who appreciated the advantages and didn't mind the weaker points of the system. The story goes, that at some point in the mid 1970's there were talks about licensing the system to Philips as well, but Philips chose to use and produce inline (not precision inline or PIL!) tubes and the only Trinitron licensee that I know of was Standard Elektrik Lorenz who only sold their production to Sony and Wega (owned by Sony) anyway.

If the wires were horizontal, the phosphor stripes would also have to be, and the scan lines would be of alternating colours. Probably as big as a nightmare (or bigger) to get to work anywhere near decently as the beam indexing system. Or the scan lines would have to be vertical, making it incompatible with normal TV transmissions.

[19Seventy7]

What is a beam index design? Was trinitron basically a way of making a TV without paying fees? What were philips’ in line tubes, how are they different from PIL? (I’d guess maybe convergence etc?)

Once sonys’ patent ran out, didn’t many other companys copy the design under different names?

That makes sense about the wires and phosphors, in theory the horizontal could work if the transmissions were compatable, even if a little bit more work was required?

Thanks

[Maarten]

Only Mitsubishi thought it was worth it to construct a Trinitron-like tube. They called it Diamondtron.

A horizontal mask would probably work to keep design staff busy for years, as did many early colour designs that didn't make it to market.

What a beam index type tube is, you should look it up as that's a bit too broad and large a subject to type here. Worth mentioning is, though, that Sony did succeed to put out a smaller beam index design later. They called it Indextron.

The motives to keep working on own tube designs? They were Sony.