12" P4 Phospher CRT

[Greycon]

Hi, after many years of searching, I have just become the proud owner of a vintage Lear Siegler ADM-3A computer terminal from the 80s. It works but has some minor screen issues.

I would like to replace the CRT. The maintenance manual says the CRT is a 12" P4 Phospher CRT. I will try to attach a photo.

Do any of you good folk know if it's still possible to source these? I live in Ireland, so a UK source would be great.

[hamid_1]

As far as I know, new CRT's are no longer being made, but you can sometimes find new old stock (NOS) ones (usually expensive) or salvage one from another computer monitor or portable TV. Your tube should have a type number label on it somewhere, accompanied by a warning about high voltage and risk of implosion. The type number will probably contain the number 31 as it's a 12 inch or 31cm tube. Post the type number if you can find it. A large range of tubes are likely to be possible substitutes.

However, before replacing the tube, make sure it is actually faulty. What kind of "picture issues" were you having? (Take a photo and post it here if possible.) Typical symptoms of a failing CRT include low brightness, weak contrast, poor focus that often gets worse when the brightness is increased. A CRT that has not been used for many years will sometimes show these symptoms initially, but will often improve after being run for a few hours. Try this first. Replacement of a CRT should be a last resort, after you have eliminated all other possibilities such as faulty electronic components in the monitor or the computer itself.

[McMurdo]

They're certainly still available but expect to pay £120 or so delivered. You will have to transfer and set-up the yoke assembly and adjust any correction magnets yourself.

[Argus25]

To replace this sort of CRT there are two sources I would go to first.

Richardson Electronics in the USA have many industrial and computer CRT's. I was even able to source some pre-ww2 P4 CRT's from them in the past. Many rectangular types like this.

Then you could always ask the Ebay seller Newtubes, who may have the same or an equivalent. They have large stocks.

Finally if that fails, post on the Vintage Computer Forum in the USA. Some of the members there have computer CRT's they sell/exchange etc.

I don't know of UK sources for this sort of CRT, but there maybe is a similar size/shape neck dia/heater voltage/gun design and deflection angle CRT used in a UK made TV that could be compatible.

The first step is to search the part number that will probably be
12 something something P4. Also, you might more easily find a green one part number, 12 something something P1.

(most likely I would guess that you want to replace it because of Phosphor burn ?)

[Richard_FM]

I wondered if you could source a 12" CRT NOS CCTV monitor with a compatible tube in, they occasionally turn up on eBay and at swap meets.

At November's Golborne meet I picked up a 9" Sanyo monitor made in 2005 which was NOS, for a single figure price.

[Greycon]

Originally Posted by hamid_1

However, before replacing the tube, make sure it is actually faulty. What kind of "picture issues" were you having? (Take a photo and post it here if possible.) Typical symptoms of a failing CRT include low brightness, weak contrast, poor focus that often gets worse when the brightness is increased. A CRT that has not been used for many years will sometimes show these symptoms initially, but will often improve after being run for a few hours. Try this first. Replacement of a CRT should be a last resort, after you have eliminated all other possibilities such as faulty electronic components in the monitor or the computer itself.

Hi, the terminal is in transit from Spain right now, but the seller sent me a photo describing a "Dark Area" in the centre 80% of the CRT. Picture below. Maybe when I fire it up (If it arrives intact) it will not be very bad. But I was just doing my homework, as I figured that if I do need a CRT it might take me some time to get it. I didn't realise that it might start to "recover" with use.

Thank you for all the pointers. I have a most excellent Lear Siegler maintenance manual (Full hand crafted schematics, and circuit descriptions - they don't make them like that anymore) and the part number listed for the CRT is a BBRC (Ball Brothers Research Corp) part no. 1-017-0737. When the thing finally gets here I will see whether there might be a more specific part number on the actual CRT.

[Greycon]

I will have to start watching the UK swap meets - there isn't a big enough population of enthusiasts here in Ireland to promote such events, sadly.

In the worst case, if I get a new CRT, is there much involved with moving the yoke and aligning it? I'm a 5V guy, and I have to say the whole CRT area makes me a bit nervous. But I do know about discharging the high voltage charge If you don't hear from me in 2 months...

[McMurdo]

Richardson Electronics in the USA have many industrial and computer CRT's

Luckily they have a UK office as well, they're in Lincoln. Their tubes are branded 'National'.

[Greycon]

The aforementioned "Dark Area"

[Lloyd 1985]

Looks like it has the possibility of being 2 things, either the CRT has been damaged and has air in it, which has discoloured or even blown off the phosphor, though that usually makes a circular patch,if it’s that then you will need a new tube, or it could be like I have seen on Shango066’s YouTube, where the CRT has a bonded safety glass implosion guard, and it has developed a cataract, where the glue has gone cloudy round the edges, which is fixable if you are brave enough!

Regards
Lloyd

[McMurdo]

looks a bit to me like phosphor burn as it's vaguely raster-shaped. I know our Systime terminals at college which were similar to this one had all sorts of over and undersized rasters, some so dazzlingly bright they had flyback lines on them for most of their careers.

[Lloyd 1985]

I’ve done a bit of googling, and it seems these do have a bonded safety glass implosion guard, and they also suffer from the cataract problem, there are a few YouTube videos on them too.

Regards
Lloyd

[cmjones01]

Actually, that dark patch looks to me a bit like there's some shield attached to the tube face which is starting to peel off around the edges. On a 1970s device like that terminal, it's unlikely to be an American-style implosion guard (cf shango066's adventures at removing them on YouTube) but more likely just an anti-glare coating or sheet of some sort. It may be possible to just peel or scrape it off and either leave as is or replace with an alternative.

Chris

[cmjones01]

Ah, crossed posts with Lloyd! So it could very well be a bonded implosion guard. Then e Uither putting up with it or replacing with another CRT is probably safest. I don't know about US products like this one but in my experience far Eastern monochrome CRTs are pretty interchangeable - I've even swapped a 9" for an entirely different 12" long persistence tube and it worked fine. They're easy to set up especially in comparison with colour tubes.

Chris

[Greycon]

Chris, is that the sort of thing you, or someone you know would do for me for the right price? I am a bit of a coward when it comes to lumps of glass containing little or no gas. Apologies if this is against forum etiquette, and if so please disregard.

[cmjones01]

Well, if you and the terminal were in Warsaw I'd be happy to help you out, but otherwise I don't think the economics stack up too well!

Chris

[Greycon]

Fair enough, I read the Cambridge bit of your address and thought I would make a nice trip across the Irish sea and spend a night or two there. THanks anyway Chris.

[linescan87]

I'll could help you out with this for some beer tokens, feel free to PM me.

[dragonser]

Hi,
I also have a ADm3a, and I seem to remember that something slightly different happened with the shield in front of the crt. Although it is not easy to get access I can try to take a photo if anyone is interested..

[Greycon]

That would be great, if you would be so kind. Is your ADM3a still working?