I have a VT320 with a pretty bad case of Being Old. The screen is so dim that even with all the lights off in the basement, it's difficult to read (and if it gets switched to 132-character mode, next to impossible). I know surplus caches of these CRTs pop up every once in a while, and I know other mono CRTs of the same size are often mechanically and electrically compatible, but I'm a bit at sea. Does anyone have pointers for acquiring such things? The current tube is amber, but I really don't care what color it is as long as it's legible. Failing that, how well do rejuvenators really work on these? My understanding is that it's usually a pretty temporary fix at best (like Retr0Brite). - Dave
Well, Retrobrite is for the plastics, not the CRT itself. On Sunday, May 1, 2016, David Riley via vcf-midatlantic < vcf-midatlantic@lists.vintagecomputerfederation.org> wrote:
I have a VT320 with a pretty bad case of Being Old. The screen is so dim that even with all the lights off in the basement, it's difficult to read (and if it gets switched to 132-character mode, next to impossible). I know surplus caches of these CRTs pop up every once in a while, and I know other mono CRTs of the same size are often mechanically and electrically compatible, but I'm a bit at sea. Does anyone have pointers for acquiring such things?
The current tube is amber, but I really don't care what color it is as long as it's legible.
Failing that, how well do rejuvenators really work on these? My understanding is that it's usually a pretty temporary fix at best (like Retr0Brite).
- Dave
-- Normal Person: Hey, it seems that you know a lot. Geek: To be honest, it's due to all the surfing I do. Normal Person: So you go surfing? Normal Person: But I don't think that has anything to do with knowing a lot... Geek: I think that's wrong on a fundamental level. Normal Person: Huh? Huh? What?
On May 2, 2016, at 4:27 PM, Joseph Oprysko <joprysko1@gmail.com> wrote:
On Sunday, May 1, 2016, David Riley via vcf-midatlantic <vcf-midatlantic@lists.vintagecomputerfederation.org> wrote: I have a VT320 with a pretty bad case of Being Old. The screen is so dim that even with all the lights off in the basement, it's difficult to read (and if it gets switched to 132-character mode, next to impossible). I know surplus caches of these CRTs pop up every once in a while, and I know other mono CRTs of the same size are often mechanically and electrically compatible, but I'm a bit at sea. Does anyone have pointers for acquiring such things?
The current tube is amber, but I really don't care what color it is as long as it's legible.
Failing that, how well do rejuvenators really work on these? My understanding is that it's usually a pretty temporary fix at best (like Retr0Brite).
Well, Retrobrite is for the plastics, not the CRT itself.
Yes, all I meant to say is that to my understanding, it's similarly temporary, and the effect of a rejuvenator on a CRT tends to revert similarly quickly. - Dave
On Mon, May 2, 2016 at 4:47 PM, David Riley via vcf-midatlantic <vcf-midatlantic@lists.vintagecomputerfederation.org> wrote:
Yes, all I meant to say is that to my understanding, it's similarly temporary, > and the effect of a rejuvenator on a CRT tends to revert similarly quickly.
It can be, but, what it's really doing is burning off the outer coating of the cathode, and exposing more emissible material. This can be temporary, depending on tube construction, but it's been my experience that most mono tubes take to it very well and hold up nicely. Some tubes, notably Sony color tubes... don't rejuvinate. Not at all. And some, like 90's era Zenith tubes as used in some arcade monitors - will revert within a week of use. But I've got mono tubes I've zapped that are still fine, years later. Also, when the tube is that dim - you have nothing to lose. Doesn't hurt to try to get a little more use out of it. -Ian
On May 2, 2016, at 4:55 PM, Ian Primus via vcf-midatlantic <vcf-midatlantic@lists.vintagecomputerfederation.org> wrote:
On Mon, May 2, 2016 at 4:47 PM, David Riley via vcf-midatlantic <vcf-midatlantic@lists.vintagecomputerfederation.org> wrote:
Yes, all I meant to say is that to my understanding, it's similarly temporary, > and the effect of a rejuvenator on a CRT tends to revert similarly quickly.
It can be, but, what it's really doing is burning off the outer coating of the cathode, and exposing more emissible material. This can be temporary, depending on tube construction, but it's been my experience that most mono tubes take to it very well and hold up nicely. Some tubes, notably Sony color tubes... don't rejuvinate. Not at all. And some, like 90's era Zenith tubes as used in some arcade monitors - will revert within a week of use. But I've got mono tubes I've zapped that are still fine, years later.
Hm, worth a shot, anyway. I've always been puzzled about the reversion mechanism; it doesn't make a lot of sense from a chemical or physical standpoint unless the tube is a little gassed (in which case I'd expect other problems). I don't know a thing about rejuvenators, but it seems like the B&K 440 is widely available for decent prices on eBay. Would that be suitable for a mono tube? - Dave
I have a VT320 with a pretty bad case of Being Old. The screen is so dim that even with all the lights off in the basement, it's difficult to read (and if it gets switched to 132-character mode, next to impossible). I know surplus caches of these CRTs pop up every once in a while, and I know other mono CRTs of the same size are often mechanically and electrically compatible, but I'm a bit at sea. Does anyone have pointers for acquiring such things? The current tube is amber, but I really don't care what color it is as long as it's legible. Failing that, how well do rejuvenators really work on these? My understanding is that it's usually a pretty temporary fix at best (like Retr0Brite). - Dave
Rejuvinators are maaagic! They burn the phosphor off the gun or something by hitting it with high voltage (110-120vac I'd guess.) But, it can go south and kill the crt. But if the CRT is weak, what's to lose? The rejuvinators can test and show you how good or bad the guns are, and then you can proceed to zap em and retest. But that isn't the only potential for issue. Electrolytic caps that have gone weak in your terminal might be an issue. So replace all of those if this is full on project. Do that first. It is possible to turn up the output from the flyback, there is usually a screen and focus potentiometer so you can turn up screen voltage (if you see the raster scan lines it's too much if such a thing exists on terminal) and you can focus it. BUT, if the tube is weak you will be driving the board harder, and could lead to early failure. The big thing I think might be an issue is the rejuvinators have a set of CRT socket adaptors and a list of CRT models and numbers to use for rejuvination. I'm not sure that dumb terminals were the intended market for such a process, so you might need to look into things a bit harder and build a custom adapter. The arcade people are mostly into B&K/BK rejuvinators. This could probably stand to be figured out for NeXT displays as well. Also, put the CRT face down when you're rejuvinating it.
At the end of the gun is a little can with emissive material. IIRC it's barium. When you hit the tube with a rejuvenator it will heat the filament up extra hot to get the material nice and warm, then give it a zap to hopefully blow away any crust that's formed on the top of the material. The danger is that when you do this it can also boil off the remaining material. If you get really aggressive you can blow away all the material! But like you said... if the tube is weak / junk anyway there's little risk. Even if it's short lived at least you get some more good hours out of it. If you want to lean more about CRT rejuvenation, and other repairs I suggest checking out bandersentv on youtube. -J On Mon, May 2, 2016 at 5:49 PM, Ethan via vcf-midatlantic <vcf-midatlantic@lists.vintagecomputerfederation.org> wrote:
I have a VT320 with a pretty bad case of Being Old. The screen is so dim that even with all the lights off in the basement, it's difficult to read (and if it gets switched to 132-character mode, next to impossible). I know surplus caches of these CRTs pop up every once in a while, and I know other mono CRTs of the same size are often mechanically and electrically compatible, but I'm a bit at sea. Does anyone have pointers for acquiring such things? The current tube is amber, but I really don't care what color it is as long as it's legible. Failing that, how well do rejuvenators really work on these? My understanding is that it's usually a pretty temporary fix at best (like Retr0Brite). - Dave
Rejuvinators are maaagic! They burn the phosphor off the gun or something by hitting it with high voltage (110-120vac I'd guess.) But, it can go south and kill the crt. But if the CRT is weak, what's to lose? The rejuvinators can test and show you how good or bad the guns are, and then you can proceed to zap em and retest.
But that isn't the only potential for issue. Electrolytic caps that have gone weak in your terminal might be an issue. So replace all of those if this is full on project. Do that first.
It is possible to turn up the output from the flyback, there is usually a screen and focus potentiometer so you can turn up screen voltage (if you see the raster scan lines it's too much if such a thing exists on terminal) and you can focus it. BUT, if the tube is weak you will be driving the board harder, and could lead to early failure.
The big thing I think might be an issue is the rejuvinators have a set of CRT socket adaptors and a list of CRT models and numbers to use for rejuvination. I'm not sure that dumb terminals were the intended market for such a process, so you might need to look into things a bit harder and build a custom adapter. The arcade people are mostly into B&K/BK rejuvinators.
This could probably stand to be figured out for NeXT displays as well.
Also, put the CRT face down when you're rejuvinating it.
-- Jason Perkins 313 355 0085
But like you said... if the tube is weak / junk anyway there's little risk. Even if it's short lived at least you get some more good hours out of it.
Eh I've got a monitor or two that have been rejuivinated (arcade games.) I don't run them 24x7, they're only used here and there and they've held up fine. I've seen some other ones that really came to life after a capacitor replacement alone.
The VT320 CRT is kind of unusual - finding a replacement might be difficult, as the profile is a bit different than the most common tubes. I have several surplus tubes, I can check to see if I have a spare that'll fit a 320, but I don't believe so. The ones I have are mostly for 220/100 and similar monitors (which is a fairly large spectrum), and a few other odd types. That said, just because it's dim doesn't mean it's unusable. Rejuvinating a CRT does work pretty well - especially for a monochrome text display. Bring it to the next workshop (and let me know ahead of time), and I'll bring one of my CRT rejuvinators. By zapping the tube, you can restore the emissions quite a bit, and, in the case of a mono terminal tube, you can restore a LOT of life. Tracking can suffer as the tube ages, but this is mostly a problem for TV tubes, which are expected to produce gradient images. On a text display, you can get away with a lot. Case in point, Jonathan had a little CRT in a tiny display he brought to VCF. The tube was *zorched*. Very weak, lots of hours, almost no emissions. Rejuvinating brought back a lot of emissions, but the cutoff point is still toast, it won't track - but it now produces a perfectly legible, bright, text display, where it was completely unusable before. Also, remember, the VT320 has a sub brightness control inside. You will probably find you can just adjust that and make it more legible without even touching the tube. But rejuvinating it ought to make it usable. I've had very good luck with rejuvination - some tubes don't last, but many do. It's well over a 50% success rate. The ones that don't respond well are mostly color tubes from certain manufacturers (Sony, Zenith from the 90's, etc), and some very old TV tubes. Another option, to eek the last bit of life out of the tube, is to boost the filament voltage. This is a last resort, and will shorten the life, but, if it's unusable and won't rejuve, bumping up the filament voltage a bit will let you get the last bit of use out of it, and again, the results can be surprising. No guarantees, of course - it's always a bit of a gamble whenever you do any of this, but, I'll wager that one zap on the rejuvinator and a bit of tweaking to the internal brightness controls, and it'll look perfectly fine for years. -Ian On Sun, May 1, 2016 at 2:52 PM, David Riley via vcf-midatlantic <vcf-midatlantic@lists.vintagecomputerfederation.org> wrote:
I have a VT320 with a pretty bad case of Being Old. The screen is so dim that even with all the lights off in the basement, it's difficult to read (and if it gets switched to 132-character mode, next to impossible). I know surplus caches of these CRTs pop up every once in a while, and I know other mono CRTs of the same size are often mechanically and electrically compatible, but I'm a bit at sea. Does anyone have pointers for acquiring such things?
The current tube is amber, but I really don't care what color it is as long as it's legible.
Failing that, how well do rejuvenators really work on these? My understanding is that it's usually a pretty temporary fix at best (like Retr0Brite).
- Dave
participants (5)
-
David Riley -
Ethan -
Ian Primus -
Jason Perkins -
Joseph Oprysko