Plenty of readers will be familiar with CRT televisions, not least because many of us use them with retrocomputers and consoles. But perhaps fewer will have worked with CRTs themselves as components, and of those, fewer still will be familiar with the earlier generation of tubes. In the first few decades of color TV the tubes were so-called delta gun because their three electron guns were arranged in a triangular form. [Colorvac] has put up a video in which they demonstrate the reconditioning of one of these tubes from a late-1960s Nordmende TV.
The tube in question isn’t one of the earlier “roundies” you would find on an American color TV from the ’50s or early ’60s, instead it’s one of the first generation of rectangular (ish) screens. It’s got an under-performing blue gun, so they’re replacing the electron gun assembly. Cutting the neck of the tube, bonding a new neck extension, and sealing in a new gun assembly is not for the faint-hearted, and it’s clear they have both the specialist machinery and the experience required for the job. Finally we see the reconditioned tube put back into the chassis, and are treated to a demonstration of converging the three beams.
For those of us who cut our teeth on these devices, it’s fascinating.
I’ve seen this done, on the old delta gun arrangement and the newer PIL 90 and 110 degree tubes, it’s a useful new lease of life but the tubes never lasted as long as a new one did, the focus went first which made me suspect they weren’t pumped down and “gettered” as well as a new faftory one.
Wow! Quite a project, but for people who still enjoy CRT goodness this looks like the future.
Not really, you can only do it once or twice per CRT and you have to be able to ensure a supply of suitable new gun assemblies, plus the phosphors wear out and shadowmasks/aperture grilles get damaged.
That’s fine, it will buy enough time for people to figure out how to make the whole tube again.
We know how to make them. We just don’t do it anymore. It’s not something you do in a shed. But for specific purposes crt are still being made.
Assembled. Nobody is making new tubes anymore. It’s the manufacture of components where expertise has been lost / forgotten.
It’s an incredibly niche market and it won’t happen in any kind of volume.
Colour CRTs are considerably more complex than Nixie tubes or simple vacuum tubes/valves, perhaps an artisan like Dalibor Farny may produce a few a year but they will be eye wateringly expensive and production numbers will be tiny.
Was this a common repair once upon a time? Or is it only a thing now because of rarity?
It was pretty common, at least in the UK, you would send off a CRT for exchange with a regunned one.
Ads in the UK magazine Television and Television Servicing at World Radio History, page 55 of this one for example: https://www.worldradiohistory.com/UK/Practical-Television/80s/Television-Servicing-UK-1982-06.pdf
No, not on commodity televisions. Even replacing the picture tube was rare, but occasionally would occur if the customer wished to pay for it. By the time this one was built, you could usually buy a newer, better set. CRTs usually to took years to degrade to the point of not being able to refresh enough to give a passable picture, and by that time the set usually looked a bit dated, design wise.
This art was strictly for very niche, expensive, industrial CRTs. I worked in a TV/Radio/Hi-Fi repair shop back in what I would call the “cassette” era, and the only CRT work beyond a Picture tube tune-up that I recall, was replacing a CRT with one from a cannibalized set, which we had a basement full of. CRTs, other tubes, tuner modules, Flybacks, adjustment pots, all had limited enough variability to be able to interchange used parts fairly readily, and time in shop added up if you had to drive out to a supplier, so it made good sense to use a scrapyard business model at the time. By the time the “CD” era was in full swing, the disposable TV/Audio (“BPC”) industry forced most shops to close their doors.
To be clear, this is a purely USA perspective.
I’m pretty sure the last fellow doing this kind of work here closed his doors about three years ago.
CRT rebuilding used to be fairly common back when TVs used vacuum tubes. CRTs didn’t last as long as modern ones either.
I think it went better when CRTs were powered by proper power supplies.
In the 1950s or so, TVs still ran on mains directly and weren’t stabilized.
This changed when plastic cabinets and camping TVs got more popular, I think.
Portables had the ability to run off 12v or 13,8v DC power source (car battery, lab PSU), so they had a need for a power supply anyway.
By that time, it made sense to derive all higher voltages from this DC voltage.
This added for stability. Also, IC based flyback control was better or more stable.
It were the small things that helped, I guess. The CRT tubes itself didn’t change so much, I think.
Very old monochrome CRTs weren’t bad, I think. But the surrounding technology was, maybe, due to economic considerations.
Properly designed b/w studio monitors from the early days could be quite longelived, too.
The technology was there in principle, just not available to consumers.
My first job was working at a TV shop (Paul’s TV) in the mid ’70s. Customers would often choose to buy a new set when the CRT died, but that was not universal. We replaced a couple of CRTs a month in a fairly small shop. We usually got rebuilt tubes, as covered here, from an Indianpolis company called “Silver Glow.”
I still remember the nigthmare that adjusting the convergance could be. A panel of as many 10 or so potentitiometers, all of which interacted with each other. Inline gun tubes were easier to converge than delta gun tubes.
Some people would pay a fortune to get color sets from the ’50s repaired/restored because the nice wooden cabinets matched their furniture. I remember rewinding coils for some of them when the forms had become brittle and crumbled. A lot of expensive labor. We also restored radios from the 30s, lots of labor there too. I usually wound up with these jobs. I made a lot more than my friends who worked at gas stations and shops.
We used to get a few customers a year who wanted to keep their old cabinet TV so were willing to spend whatever it cost, we also did what I guess would be called a restomod and transplanted the guts of a new set into the old cabinet for a couple of sets a year
We also converted a few imported televisions a year, mostly PAL or multistandard sets where the only significant changes were to remove the sound IF filters and install 6MHz ones for the UK but occasionally we’d get paid to go as far as a transplant.
In our workshop regunned tubes were fitted to rental stock, refurbed second hand sets and customer sets, it wasn’t the bulk of our work but it definitely wasn’t uncommon to fit a few ‘new’ tubes a month.
I had no idea the phosphors could tolerate exposure to air. I’ve always assumed they oxidize instantly or something if the tube cracks.
The phosphors are aluminised, only very old and ugly American B/W tubes weren’t, but those had the ionic trap to avoid the premature dead of the central section of the phosphors.
Aluminizarion was a better alternative to the ancient ionic trap, I guess that, as a side effect it protect the phosphors from oxygen, at least for some hours or days.
They used to sell “tube brighteners” for picture tubes that had gone dim. They were mounted in series with the connection socket to the back of the tube and were basically just transformers to crank up the filament voltage.
When I was a teenager a neighbor had an old black and white TV they wanted to get rid of, and I grabbed it for my bedroom. They had already added a tube brightener but you could still only barely see the picture, so I got if for free. When I took it apart I discovered that the only thing wrong with it was that the protective glass in front of the picture tube was thick on the inside with grease and tar deposited by the very heavy smokers in that family. I cleaned it off and had a nice bright picture. Economic Darwinism.
Tube brighteners worked on sets that powered the CRT filaments from 60Hz AC, but later sets that powered their heaters with a tap on the flyback transformer ruled out this device.
Sure, they ruled out that device, but it was usually easy to add a winding or two around the flyback in series (and phase) with the heater winding to boost is a volt or so..
Btw there where tube regenerators that did not require opening the tube.
They used a voltage applied between the cathode and the focusing electrodes and/or ultrasonic current to clean up the cathode.
I owned one and I used it many times.
The mileage varied depending the tube condition, tube maker and so on, but most of the time did work very well
The circuit of basic models was pretty simple to build
https://www.grix.it/viewer.php?page=1476
The boring part was to assemble all the cables needed to make it universal, given there where dozens of socket standards. Practically you needed something like 15 cables to cover most of the BW and Color CRTs. But with 5/6 cables you had covered say the 90% of the most common types.
Obviously you could use a single cable terminated with crocodile clips, but in that case mistakes were around the corner.
Commercial models were obviously provided with everything you needed, but they weren’t cheap, just like any equipment built in small number.
I remember seeing ads in TV Guide selling turnkey operations for setting up your own CRT rebuilding business. I also remember that our RCA 21″ “round-tube” (our first color TV) went through a CRT about every two to three years, so I imagine there was a shortage of tube rebuilders.
CRT has high voltage even when unplugged. Danger
And water is incredibly wet.
In many ways CRT is still the best display tech ever made. Nothing beats their motion resolution and ability to switch res without processing.
I can see details on my crt that are barely visible on my 4k oled.