CurtPalme.com Home Theater Forum

[deronmoped]

What Does It Take to be a Picture Tube Rebuilder, Really?
(From: Charles Godard (cgodard@iamerica.net).)

Back in the late 50's A Tech friend of mine built a picture tube rebuilding plant from scratch. He made a living with it for a few years selling rebuilt b&w tubes. Everybody around said he sold the best rebuilt tubes that you could get. He said the secret was in the good vacuum pump and that he used and the amount of time that he pumped down the tube.

He always said that a tube could be made to last practically forever if you could get a high enough vacuum on it. The only real money he put into his plant was in the pump.

A few years ago he retired and brought the whole thing down to my shop for storage. It was a marvel to behold. The cooker was an old upright deep freeze with a pyrex pie plate for a window. The lathe where he welded the tube necks onto the tube was built of scraps of angle iron with a washing machine motor. The device that he used to cut the necks off of the tube was a model railroad controller with a homemade foot pedal and a couple of whittled down broomsticks with metal tips shaped so that you could easily fold the nichrome wire around the tube neck. He said it was the only transformer he could find, at the time, that would hold up to heat the wire hot enough to cut the neck off of the tube. It was very low voltage but would supply hi current.

He said he had the most trouble when designing the inductance heater but finally got it built with the help of a local genius who had built one of our local TV station's nearly from scratch back in the 50's.

In addition to the tube plant, he also designed and got a patent on a cotton picker. I've got a copy of his patent on display in my shop. Some of us only half believed him for years, when he said he had the patent, but when he died, we searched the shop and found his patent papers hidden away in a file cabinet of old Sams Photofacts.

We found the contract where he sold the rights to build and market the picker for a $500 per picker royalty. The guy he sold it to took the patent and went to a nearby state, borrowed $200,000 from the bank with the Patent as collateral then skipped the country. My friend never got anything from his invention, and some of his design ideas were later stolen and incorporated into some one of the big name picker manufacture's products.

Those old guys were something else. They could start with a few old scraps and build something worthwhile and useful.

Speaking of patent's, I've also seen the original patent for the hinges RCA used to hold up the tops on the old console stereo's. I made a service call a few years ago, and the guy's widow showed me the patent and his original prototype hinges. The only thing is, they took the idea from the patent and redesigned it so they wouldn't have to pay our local guy for the hinges. RCA's redesign didn't work as well as his original, but was recognizable as his original with only a couple of changes. RCA 'did him' about the same way they 'did' Philo Farnsworth.

When I get a slack spell, I'll try the inductance heater to see if it still works. If it does, I try it on the tubes and let you know. I believe you called it a Tesla coil?

[Tim in Phoenix]

Keep dreaming

No one here wants to spend any money on anything. I have new tubes here, $3,300.00 MSRP that I can't get $300 for.

[gjaky]

I also think that more good tubes are thrown away these days than actually used up...

[garyfritz]

Cool story! The guy sounds like quite a MacGyver.

I doubt he used a tesla coil for an inductance heater. Tesla coils are major step-up transformers. They produce up to millions of volts at high AC freqs.

[Curt Palme]

There were CRT rebuilders in most cities. We had one locally. While he didn't rephosphor, he did a stellar job of taking off the old electron gun and putting on a new one.. when they were available. Back in the 80s, I spend $1000s with him over about a 10 year period. He couldn't do CRT projector guns, the guns weren't available at the time.

[Curt Palme]

There were CRT rebuilders in most cities. We had one locally. While he didn't rephosphor, he did a stellar job of taking off the old electron gun and putting on a new one.. when they were available. Back in the 80s, I spend $1000s with him over about a 10 year period. He couldn't do CRT projector guns, the guns weren't available at the time.

[cmjohnson]

If you really wanted to do this, you could. And I'd bet that VDC would be glad to sell you all the equipment needed to do it,
at a very reasonable price, and even provide you with the process documentation and personnel training required.

For a price.

Right now the toughest part of making NEW tubes would be to ensure your supply of glass parts.

The glass components of the tubes that are of most interest to us are made by Nippon Glass Works (you may note that on the bell of any Panasonic family CRT there is a big N molded into it...guess what that stands for?) and the other major player in the field is Asahi Glass Company.

I don't know with any degree of certainty if either still makes CRT parts. But the bell and the faceplates on "our" tubes are molded parts provided by one or both of those companies.

I never found out precisely which OEM manufacturer makes electron gun assemblies but there are still companies that make electron guns and I expect that there still will be some for a number of years to come. There are some niche markets where
CRTs are still a requirement.

And then you'd need the phosphor chemistry. That is the last truly specialized product you'd need that goes into a new or rebuilt tube.

You'd need HF acid handling equipment and the training to use it. It's used to super clean and etch the glass in preparation for the phosphor layer. Although it's a mild acid in strength as far as most manufacturing processes go. it has unique hazards to human health. Basically if you get it on you it binds to any calcium it can find in you. It'll eat your bones. It's also particularly horrible to your eyes.

The phosphor is applied in a liquid solution, literally just poured into the bell of the tube. It's allowed to settle out of solution for a set amount of time and then the excess is slowly and carefully poured off, ensuring that the layer is even and undisturbed.

It's then set aside to dry for a while and when it's dry, a lacquer coat is sprayed into the tube, sealing the phosphor layer.

The phosphor mix has a binding agent applied to it which helps it to adhere to the glass.

I can't remember the exact order of every process but at one point the tube gets baked to remove the no longer needed lacquer,
and it also gets an aluminzation coating behind the phosphor layer which serves multiple purposes.

An interesting note here: Phosphor wear and burn is believed to not really be any burning of the PHOSPHOR, but of the binding
agent and of any remaining lacquer, instead. Some people believe that if they could find a way to eliminate the use of those
binders and lacquer they could make a tube with a phosphor life that is orders of magnitude greater than what we have now.
And then the limiting factor becomes the life of the cathode. Which doesn't so much as wear out as become contaminated due to chemical interactions with what little air is left in the tube. So the harder the initial vacuum, the longer the tube life. Hence the importance of the getters, which scavenge gases out of the tube. Usually they consist of beryllium. Which, I must note, is toxic stuff, if in a finely powdered form. When the getter is fired, it splatters itself onto a portion of the tube wall, in an extremely fine adhered powdered form. SO don't breathe the stuff!

It would be interesting to see if any manufacturer of quantum dot phosphors would be interested in providing samples of the phosphors in colors that are of greatest interest for home theater enthusiasts and see if quantum dot phosphors are compatible with projection CRT technology . If so, then rebuilding tubes with the CORRECT HD spec color coordinates and needing no filtered C elements would become possible. And possibly with greater phsphor life. Maybe even more output.

Individually, all the processes in tube (re)manufacture are simple and can be taught to anybody who is reasonably competent.

But putting the tube together requires a moderately skilled glassblower. An expert is not needed, but if you have no experience blowing glass, you're not ready to assemble the glass components of the tube.

[matt697845]

[Tim in Phoenix]

[CIR Engineering]

[digitalayon]

[digitalayon]