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Hello again to all,
@SquirrelBoy,
Thanks for your comments. What i have learned, is the result of a lifelong interest in CRT technology, reading many books such as Peter Keller's masterpiece "The Cathode Ray Tube", then from close contact with the RACS team over 6 years.
"A lot takes places between a few people": yes, gratitude and acknowledgment must be given to people who gave great dedication and invested a lot of $$ into CRT rebuild attempts such as John Folsom jr, Bob Galanter, John Yurkon, Steve McVoy who impulsed the entire ETF CRT rebuild project and the many UK/US/German/Dutch/Italian/French customers who trusted Hawkeye and RACS to bring alive again their vintage screens.
If hope is more alive today than before to make this project happen, these driven individuals must each be thanked for the years of behind the scene groundwork & experience done in the background.
The very fact that this new "CRT Rebuild Central" Forum now exists is a great achievement in itself.
"I wonder if adding some of the newer gun's design ease to the older tubes will make for greater success when the guns have to be rebuilt on the old color tubes in particular...."
Personally, i don't think so. This would entail a re-design of the electron optics design, a major task to say the least. Bear in mind that the original designs were conceived by teams of highly qualified engineers with ample funds and collective decades of experience in designing them. A new, simpler to build design would have to be compatible electrically with the original CRT's specs - a tall order to meet. Think about it, the people who had the knowledge are all in their 80s-90s today and in this day of digital flat screens, the art is on the teetering-edge of being lost.
"I wonder if in the future the rebuilding will even require the reuse of the base, and the glass work will need to be rethought as well so as to accommodate new thinking for parts salvage when rebuilding tubes."
A new base is mandatory for 3 main reasons:
- a stem is needed to mate to the vacuum pump assembly, and no, you cannot "reopen" a sealed stem.
- In the case of Pre-War CRTs, the glass used was Pyrex. Now you cannot fuse together Pyrex and post-War "soft glass" because the temperature gradients differ widely = 100% breakage certainty once the weld cools. When RACS rebuilds Pyrex Pre-War CRTs, an adaptor sheath is created using "Salami slices" of glasses of different gradients. One end is Pyrex, the other is Soft Glass to mate to the new Soft Glass base/stem assembly.
Soft, so-called "electronic glass" was developped during WWII and exclusively used afterwards to manufacture electron tubes and CRTs because it can be processed at lower temperatures and is much easier to produce by flowing into molds (volume production of millions of CRTs).
The very much increased coefficient of expansion vs Pyrex is no problem when the entire CRT/electron tube uses the same type of glass throughout.
"I think Scotty most likely had a source of new guns"
True, and so does RACS, several decades worth of inventory building + buyouts of NOS parts. The problem is that a given gun will only be compatible with one specific CRT model, and if you're lucky, maybe a few models in the same brand/product range. Most of these are compatible with fairly modern CRTs, spanning the 70s to the year 2000, in other words, our "oldies" B&W from the 30s, 50s, then early color 50s tubes are not within the NOS parts readily available so entire disassembly + rebuild is the only option.
Maybe in the future, TVs of the 60s to 90s will become collectable. This is not the case now, so these guns are pretty much useless. They will be recycled and in 20-30 years, they will be sorely missed.
"My guess is that the entire rebuilding process will have to be rethought as time moves on. I had often wondered what it would be like to have to actually replace a heater and cathode. Or if a heater should be replaced, and the cathode scraped clean and new chemicals re-deposited."
Heaters are replaced. Taking a filament out of the emissive cathode sheath is near impossible - it is wound, fragile and breaks.
BTW, concerning questions about rebuilding 2.5 Volt filaments ( Predicta CRTs) RACS found out that these are no longer manufactured. And for a reason: any +/- variation in wall supply AC power has a very significant impact on the electron emission of a gun powered under such a low AC supply. Therefore the gun is replaced with a 6.3 Volt filament and a transformer is supplied with the rebuilt CRT to convert 2.5V in the TV to 6.3 VAC.
In some rare cases of non-availability of new cathodes, RACS has re-coated the original part with a new electron-emissive coating with success (some Mil-specs impossible to find Radar tubes).
@Old_TV-Nut
Hi Wayne!
"This question about guns makes me wonder if it is worthwhile to pursue a source of guns (if they haven't all dried up yet) and amass an inventory like the one Scotty had, under the assumption the rebuilding effort will be successful, but guns may not be available later."
RACS would be happy if someone saved them, but who wants guns for 70s to year 2000 guns? - too young for our "heart of target" collectible TVs, but will be desirable 20-30 years from now. Who will be willing to pay for the storage cost for the next decades?
@Electronic_M
"This method might also be useful in gun rebuilding. If only the elements that need to be worked on can be melted off or out of the glass rods(or the rods cut and new glass melted on in the appropriate place with the new elements in position), and then melted back in it might be simpler than all that welding."
Glass close to its melting point is a very difficult media to work with: high temperatures, flames & gas nearby & oozy glass. Just ask Nick about his experience. Precise positioning and remaining in position while cooling of pieces of metal in a bar of glass with millimeter tolerances is no mean feat. I suspect that the OEM producers of the time had precision machinery and automatic alignment jigs that have long gone to the scrap heap heaven today.
Spot welding is relatively easy, the difficulty lies in getting the part precisely in position in 3D space and keeping it there while the weld is accomplished.
The days of the industrial giants such as RCA, Westinghouse, GE, Sylvania, Zenith-Rauland - their lavish multi-million $ production machinery are gone forever. We will have to make-do with modest equipment and a lot of elbow-work.
Best Regards
jhalphen
Paris/France
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