Gathering data on CRT rebuild value
 

All -
I think it would be very useful to this project to poll collectors on how much they would be willing to pay to have CRTs rebuilt. Knowing this will give us a good idea of how feasible the business side of the operation is, one of the important questions that needs to be answered as we try to get this up and running. To this end I propose that we create a poll on the matter and link to it in the various TV forums to collect data. However, before I do this I would like some feedback on what others think of the idea and how I might go about actually creating such a poll.


First, what CRT types should we ask about? I propose:
10BP4
12LP4
7JP4
3KP4 (Pilot TV-37 tube)
7DP4 (621TS tube)
17DRP4 (Predicta tube)
21EAP4 (Predicta tube) (Thanks bandersen!)
15GP22 (CT-100 tube)

Second, for each of these tubes what price ranges should we ask about? For all but the 15GP22 I propose options of:
<$100
$100 - $200
$200 - $300
>$300

For the 15GP22 I propose:
<$500
$500 - $1000
>$1000

Third, how would one go about creating such a poll? I don't think this forum or the antiqueradios.com have the advanced poll options we would need.

Thanks for your input.

-Matthew

Good idea. I'd like to add 21EAP4 (predicta tube) to the list. I have three that need rebuilding. A growing pile of 10BP4s and 12LP4s too.

Just to give you some idea what it used to cost - Hawkeye was charging $300 for a 10BP4 right before he closed.

I propose adding the 21" color Roundy tubes.
21AXP22(this is the most challenging type of 21" color tube to find or rebuild, likely of similar difficulty to the 15GP22)
21CYP22
21FBP22
21FJP22
21GUP22
etc.
With how many folks collect these sets and how often folks are looking for roundy CRTs adding these to the list is a no-brainer.

Some of the 25"(23" viewable) and smaller size rectangular delta gun color tubes such as the 25GP22 might also be good to add. More and more folks are collecting them, and sooner or later the few NOS CRTs and parts sets with good tubes to pirate will dry up.

I know the purpose of this forum is the exchange of ideas, but the cart in these posts so far is being placed WAY TOO FAR in front of the horse.

Can we please deal with reality for a moment?

We don't even have a rebuilding station built, much less a solid place nailed down to set it up in. That makes talk of which CRT's to rebuild very premature, to say the least.

I think everyone thus far is running on the assumption that ETF will be the place, and I don't think anyone disagrees about that. That makes the next point of discussion what the station will look like. Bob made up a drawing I like, so let's build that.

http://www.earlytelevision.org/crt_project.html

Now all we have to do is get together and build it! Easy right? Not really, if that were so it would be done already. Everyone LIKES the idea of being able to rebuild tubes, but thus far there has been ZERO heavy lifting on getting anything actually DONE. That's because no one so far has surveyed the proposed location at ETF, or drawn up any plans to follow.

So I guess what I'm getting at here is, stop skipping straight to 'GO' when we haven't even left 'Reading Railroad' yet. The first course of action at the moment needs to be working towards a solid set of building plans we can follow, then we can start moving stuff around, running wires/pipes, ect. Once the station is built, we can move on. Everyone in favor of 'Operation build a CRT Station'?

Aye!

I'd pay $500 each for my two 30BP4 CRTs to be rebuilt. I'd also pay $75 each for about eight 3KP4s I have to be rebuilt. I have six 21" roundy CRTs I'd pay $250 each to be rebuilt.

What about the GUNS the important part. Where will you find them?

Hi All;

I am happy to see progress on the picture tube rebuilding program getting underway. I think for the sake of getting an idea on a price point and demand for tubes 7jp4-guy is just doing some market research here on demand and getting some idea on where a budget may begin to take shape.

We can imagine that Hawkeye's prices gave him coverage of costs, plus a profit to put into his being able to live. We can equate that profit to funds to keep the tv museum and the crt rebuilding station open.

That said, I think prices should be at least at first based upon what Hawkeye was charging, and of course you may have to add to that for the replacement of consumables that will grow harder to acquire as more crt companies close their doors.
I would imagine he can even give you a starting point on demand for certain types of tubes. This community can do that as well. Just start a sub page "how many of you have tubes for rebuild" Add your type, quantity, max price payable.

I would also assume, that as the crt rebuilding station is set up the first tubes will have a high failure rate due to contamination, and the fact that this "art" can not be perfected by watching the movies on youtube. I would imagine color tubes may be a few years away, and that more common B&W tubes will be the first tubes to see rebuilding success and any amount of volume production.

It is impressive to see the grand size of the station drawing. It assumes a large volume of tubes will be processed. I sure hope this can be accomplished, but I think a small less expensive test size room might be a smarter way to go, save some cash.

I am very pleased to see the crt rebuilding project make VK its home (I hope) for news. Previously any news was quite sporadic, and scattered very unorganized across several websites and un-updated for a few years in some cases, even as these sites upon launch proclaimed to be the new location for news on the project.

I would also like to see a repository of knowledge collected, on the process, chemistry, machinery, all of it, here so that the knowledge can be accessed and improved upon by individuals who may not be near the station, but may have usable ideas for the project. I have enjoyed seeing and reading, and watching the youtube procedures of the attempts with the 15G that have been posted over the years. Each new posting I find seems to contain a little bit more information on the complexity of the procedure. I for one, would like to be able to read about and understand the entire procedure of crt rebuilding.

I think in the long run, the guns will have to be rebuilt by you guys, not just rebuilding the tubes, so that is something you will have to think about while allocating space for the project.

The possibility of rebuilding guns means that maybe recovery of the cut off old gun needs to be thought about now. When cutting off a gun you now have a replacement for, may mean that old gun should be saved, and stored in a clean, vacuumed, and sealed storage locker.

Thanks for bringing the crt rebuilding project news and progress reports to VK.

Progress report:

Geoff Bourne has agreed to be the project manager for building the room at the museum where the equipment will be located. He visited after the convention, took measurements, and we discussed ideas for construction.

He will put together drawings and a bill of materials. I have agreed to price the materials so we know how much money we'll need for this project.

Geoff will select a date for pouring the floor, and bring the necessary tools. We should be able to get that done in a weekend.

Then, another date will be set to build the room.

Chuck Azar will be in touch with those on the email list, and dates will also be posted on this forum.

Something else to think about. It does no good to have a rebuilding plant if we have no guns or cathodes & teems to rebuild guns, along with the required fixturing.

We may have some guns from Hawkeye, and maybe some more from RACS at some future date. There may also be some guns available from Southwest Vacuum, if it is not already too late.

It is unlikely we will be able to rebuild 3KP4/7JP4 CRTs, because there are no guns and no stems available, at least that I am aware of.

But Nick is correct, we must wake before we run.

What became of Tektronix' CRT operations when everything went LCD? Perhaps a gun adaptable for the electrostatics might be available ?

If the project is to be done entirely for its own sake as a historic/educational exercise, then even one or two working CRTs per month at amortized costs of $2000 each or more is fine. If the project is specifically planned from the start as a self-sufficient business, then the questions of what people are willing to spend (and how many customers may exist, even) are very worthwhile. Fifty CRTs at $150 each over one year would not have a chance at paying the bills.

I would expect (or hope) that the project will end up somewhere in between my two examples, if it does succeed: CRTs rebuilt at time and material costs, but with lots of volunteer work and/or donations as well.

Ultimately, the value of a new picture tube in a set depends heavily on the value or desirability of the set itself. $300 is a lot of money just to get a brighter picture in a typical late-1940s 10-inch RCA TV, but $500 to get a 21-CT-55 or Muntz 721CV working again is almost a no-brainer to me.

I agree the thing needs to get built before even talking about pricing but... it was $300 for a normal B&W from Hawkeye.

I expect it is going to be much more expensive if it's done on a smaller scale for vintage tubes only, this is just something we'll have to live with if we want tubes for our old sets.

I doubt if it matters much if a CRT is 3 inches or 21 inches, the work and materials are the same, and honestly a 3KP4 is generally a much more desired tube than a 21" B&W (except a Predicta of course) so price being commensurate with size is not likely, like any business the retail price will ultimately depend on what the process costs to operate.

If Guns have to be hand rebuilt then I can imagine it being way more expensive.
It might turn out that the only practical application for a rebuilding station will be for Pre-war tubes and early color where price is no object.

Only 2 or 3 people are every likely to get good enough at it to do the rebuilds; will they all be local to the museum, or will they have to fly in a do a few on a weekend? As volunteers, they aren't going to be too excited to sweat out, say, a 10BP4, knowing it won't net any profit for the museum...or for them. The 10BP4, most 21" b/w's, all 18v/19v/23v/25v stuff...it would be a very long time before the demand would be there. I suspect that once everything is set up, most of the time will be spent on the "heavy-hitters", 15GP22, 21AXP22, 30BP4, the Predicta tubes would be easier and a good source of income. Personally, I'm not sure if I'll ever be well heeled enough to pay what it's worth to rebuild, say, a 3" Pilot crt.

I have no idea where I'll be in life when I retire, but I hope it won't be too far from the museum...

Hi to all,

Hello Nick,

I am worried about one essential step in the CRT rebuilding process: rebuilding the guns. For most of our vintage tubes, NOS ready to install guns simply do not exist, therefore the only way is to take apart the original gun, replace the filament(s) + cathode(s), then reassemble.

This is no mean feat: the entire electrode structure must be taken apart then reassembled in 3D space with perfect spacing & alignment geometry. We're talking fractions of millimeters in all 3 dimensions here. The issue is not only rebuilding a working gun, it must conform to the original specs for it to work perfectly in a vintage TV.

Imagine for instance that an original focus voltage called for 800 Volts but that the rebuilt gun focussed correctly only at 1000 Volts. The TV's circuitry would need to be modified or the CRT rebuilt again. And this is just one parameter among a myriad that can veer off course.

Not trying to be a kill joy here, but just trying to convey how difficult it is to do if you don't have the luxury of just taking a NOS gun out of a bin.

Two years ago, i queried François R. at RACS about doing an inverse operation to Nick's coming to France: if the ETF CRT plant was installed & ready, would he come to the US as a consultant to teach the art of gun rebuilding + iron out the bugs as the facility started to operate? the answer was "why not".

That was 2 years ago. Still i think that someone with 40 years experience in CRT/gun rebuilding would be invaluable to shorten the learning curve of the new facility.

In RACS's 35 years of operation, even when the plant had 30 employees, François R. was the only person who took apart & reassembled guns.

Question:
Would Hawkeye's Scotty accept to do this? his residing on US soil would really make things easier/cheaper.

Best Regards

jhalphen
Paris/France

Hi Jerome.

Do we know if Scotty even did this himself, or did he order his guns from elsewhere?

One of the things I was thinking.... And one reason I believe b&w tubes will be the first to be done, and color a few years behind that....


jhalphen: Would you be able to write back with detailed description and if possible pictures of the procedure used by them for the exact process used to deconstruct, and rebuild a gun? What methods are used to measure spacing on an old gun before its taken apart? Do they deconstruct the entire gun, or just the end near the heater & cathode?

Do they re-manufacture the grid emements, or re-use those components reclaimed from the old gun?

And how is that glass bar made that holds all those elements together? Is it melted and the tabs pushed into the glass bar, or some other method?

Thanks....

Hi SquirrelBoy,

I will endeavour to answer your many questions.

See 10 photos on my PhotoBucket site of the gun rebuilding process taken by RACS, showing a gun at various steps of reconstruction:

http://s281.photobucket.com/user/jha...?sort=4&page=1

If interested to see the rest, the root directory of the entire CRT rebuild process is here:

http://s281.photobucket.com/user/jha...?sort=4&page=1

Obviously much more data is required. I will ask, but it will take time.

When at RACS, i saw an assortment of measuring tools, calipers, gauges, palmers,... sorry, i don't have too much vocabulary in describing tools for mechanical measuring.

What is taken apart: depends on the gun. With modern guns, often the beam focus electron lens and G2/G3/G4 anodes can be left alone because the cathode & G1 are mechanically separate and can be reached.

With older CRTs, for instance pre-War & early color tubes, the cathode & G1 are very close or sometimes even totally hidden inside the anode structure so dismantling of the entire gun is necessary.

In this case, the anodes & metal prongs used to mount them are carefully set aside to rebuild the gun in the precise same order once the filament and cathodes have been replaced with new ones.

I do not know how the glass bars are made originally. RACS does not make them, they re-use the originals with painstaking efforts not to break them.

In their parts inventory they have NOS glass bars and if one is broken, they find a substitute which matches in length, diameter and metal inserts. There is some leeway here, the metal inserts can be to some extent bent or tweaked to match the original, after all the glass bars are only for support and do not play an active role in the electron beam's creation.

Taking the gun apart and rebuilding it is achieved by using a small electric spot-welder with various size tips used depending on the size/weight of the electrode to be welded.

PS: Bob G. took photos and described his experience in removing the cathodes on 15GP22 CRTs. Bob, wanna pitch in?

François R. is justly proud of his engineering skills and describes gun rebuilding as a mix of science, technology, known to work recipes and a pinch of witchcraft. He quoted 16 to 20 man/hours of work to rebuild a 15G tricolor gun. He describes the 3D maze of wires connecting the 3 guns to the base as "an utter nightmare" to avoid accidental shorts when mounting the rebuilt gun to its new base/stem assembly.

Best Regards

jhalphen
Paris/France

Thank you Jerome. If you would, this project is of great interest to me, I would love it if you could post more of the knowledge you have of all things crt to this thread. There seems to be a lot that takes place between a few people, while there are many more who are not directly involved in the work, but would like to know more... like me.

I see what you mean about the heater cathodes on newer guns. I have a system 3 gun by zenith and it looks like the heater cathode is a quick change on that gun. 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....

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.

I think Scotty most likely had a source of new guns, and that you guys in France did a lot more intricate work. And worked on projects a lot closer to the impossible....

Thank you again!

Scotty used new guns, some of which required welding some added parts onto a basic gun. He did not do any cathode reconstruction or construction of guns from individual electrodes on glass mountings, as far as I know.

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.

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.

I seem to recall, from IIRC a very long 60's in house RCA promotional film(or perhaps an episode of 'How it's Made') of what they did then, a scene of a monochrome electron gun being assembled where they stacked all the metal parts on a temporary alignment frame then applied the soft heated glass to the element tabs to hold all the elements together as opposed to welding the elements to tabs on the glass like RACS does.

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.

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

Well thank you again Jerome! And as I said before I hope more of this knowledge is made available for all of us to learn and carry as one of us may be the last ones with this special knowledge one day.

Have a good evening....

And I got a mild dose of the works over there. Just listening to the stories about what it used to be like during the summer with both 5-bay ovens running, plus 5 more vertical lathes going with a guy at each of them... Can you imagine how hot it must have been? :smoke:

I suppose it would be a good idea to have a rebuilding station climate controlled, at least in the area of the vertical lathe. That way you don't have to worry about cracking in cold air.

Jerome, thanks for a comprehensive reply to many of the points raised. The problems seem to split into 2 categories. Those which may be difficult but can be solved with craftsmanship and practice. And those that are a lot harder.

In the former are glassblowing skills, including the graded seals needed for Pyrex CRTs, Also the vacuum, baking and gettering techniques. These are all well known technologies, still in use for other purposes.

Things get a lot harder when replacement guns are not available. A spot welded gun can, in theory, be rebuilt using fairly simple equipment and a lot of skill. The gun of an EMI 6/6 was rebuilt this way in 1986. This is a complex hexode gun. It was rebuilt at Thorn-EMI Electron Tubes, now long gone, who specialised in photomultipliers. They certainly had the skills but not any specific jigs for that CRT. A gun assembly fused on to glass rods is more difficult. I don't know if a heater/cathode assembly can be replaced without dismantling the whole gun.

It strikes me that the hardest problem is when new heater/cathode assemblies cannot be obtained. As Jerome says, you can't remove and replace a heater from a cathode cylinder. Are h/k assemblies still available? At least they are small so storing them (in vacuo?) is not such a big problem. Making new cathodes with good emissivity and long life seems difficult. The knowhow for doing this must be almost lost.

I don't know anything about re-screening and aluminising.

Colour CRTs add a whole new set of problems.

I think others have mentioned an additional practical problem. We have a limited number of CRTs to use for learning the techniques. Each one is precious. When the original makers were making CRTs they could easily write off many CRTs as part of the development process.

It's a very brave venture. I wish all of you every succcess in keeping the craft alive.

Hi to All,

Hello Jeffrey,

Thanks! for your message.

"The problems seem to split into 2 categories. Those which may be difficult but can be solved with craftsmanship and practice. And those that are a lot harder."

"In the former are glassblowing skills, including the graded seals needed for Pyrex CRTs, Also the vacuum, baking and gettering techniques. These are all well known technologies, still in use for other purposes."

RACS does not do glassblowing. From their days from working with Corning Glass (RACS's founder was originally a Senior Engineer at Corning) they've kept an assortment of NOS glass bulbs, alas mainly in the 8-10 inch sizes so no "big" bulbs to simulate 12 inch CRTs. I've asked them to keep this glassware while huge quantities of bulbs for 19 inch & above (90° to 110° deflection angle) went to the recycler.

When several of the Pyrex CRTs developped cracks around the EHT contact, i asked them to get a quote from SIVE to know what it would cost to make a master mold for instance for a 12BP4 bulb. SIVE is a Paris company which specializes in laboratory glassware and who are experts at working with Pyrex. From previous experience with SIVE, Philippe quoted around 2000 Euros for the mold, but i never saw a formal quote. The shallow insert of the EHT metal contact is difficult to do and would probably impact the price. If the demand was high enough, it would allow to make new "Repro" 12BP4s or any other tube in popular demand.

Personally, i do not relish the idea of a new Pyrex bulb, why not use much easier to process modern electronic glass. I guess the answer is that SIVE is a Pyrex specialist and they tend to stick with what they know. They are probably not the only glass molders/blowers to exist...

"Things get a lot harder when replacement guns are not available. A spot welded gun can, in theory, be rebuilt using fairly simple equipment and a lot of skill. The gun of an EMI 6/6 was rebuilt this way in 1986. This is a complex hexode gun. It was rebuilt at Thorn-EMI Electron Tubes, now long gone, who specialised in photomultipliers. They certainly had the skills but not any specific jigs for that CRT. A gun assembly fused on to glass rods is more difficult. I don't know if a heater/cathode assembly can be replaced without dismantling the whole gun."

You've pinpointed the problem: RACS has scores of new ready to install guns but most of these are for tubes of the 60s (a few), the 70s & 80s (a lot), so they are pretty useless for our specific vintage needs.

Still, having an inventory of parts allows "to be creative" when unforeseen difficulties happen with a rebuild. I remember François R. showing me a couple of UK tubes where gun parts had been grafted from a donor NOS gun because the original was too far gone to rebuild properly.
Once you master from scientific training + decades of experience the interactions between electron beam focussing, acceleration, deflection angles & EHT, yo can juggle the parameters to make it work.

"It strikes me that the hardest problem is when new heater/cathode assemblies cannot be obtained. As Jerome says, you can't remove and replace a heater from a cathode cylinder. Are h/k assemblies still available? At least they are small so storing them (in vacuo?) is not such a big problem. Making new cathodes with good emissivity and long life seems difficult. The knowhow for doing this must be almost lost."

RACS has a huge inventory of filaments/cathodes/heaters & getters. As for new production, it has really ground to a stop for consumer CRTs. There are still specialists producing parts for high power Broadcast tubes, particle accelerators used in physics - heavy use of Klystrons here, etc.

Actually over time, the industry of CRTs simplified the product range. Philippe told me that today there are only 2 sizes of cathodes, so it it quite possible to salvage NOS ones from much more recent guns if you need a part and have no inventory.

In their opinion, there might be suppliers of new parts in China and India, after all China and Russia produce today copies of favourite audio output tubes for the hi-fi market. The hitch is that with the company scaling down to near closure, they have no incentive to meet companies in faraway lands & assess the quality of unknown parts. Also, any order would have to be in high volume, probably on the order of a 1000 at least.

They also have experience in re-coating the electron-emissive paste when some really oddball tube occasionally came in. Think Mil-spec Radar/Sonar/Cockpit Display CRTs.

I don't know anything about re-screening and aluminising.

In a nutshell, you clean the entire CRT down to transparent glass, then you rebuild the entire screen assembly:
- wash out all phosphors, Dag, etc. - many wash cycles
- clean with a diluted mix of hydrofluoric acid.
- deposit new screen - a wet suspension
- tilt CRT, pump out excess liquid
- dry
- apply a layer of cellulose for adherence of the aluminum layer
- dry
- vacuum pump & sputter aluminum
- cook to evaporate the cellulose - nasty (flammable solvents here!)
- apply Aquadag to inside of tube - not easy
By then, the bulb assembly is now ready to receive its new or rebuilt gun.

Sme nuisances that can ruin your day:
- uneven screen coating - restart from scratch
- micro-roughness of the glass on the inside surface of the screen: leads to streaks once you light up the finished tube.
- Inside Aquadag too close to gun's end: EHT flashover.

"Colour CRTs add a whole new set of problems."

Gun wise, it's triple the amount of work. Screens are inspected prior to any work because if the phosphors are damaged, nothing can be done.

No rebuilder ever deposited colour screens. Only the OEM supplier had the lighthouse projection systems for depositing the phosphors.

"I think others have mentioned an additional practical problem. We have a limited number of CRTs to use for learning the techniques. Each one is precious. When the original makers were making CRTs they could easily write off many CRTs as part of the development process."

Very true. However practical experience could be gained from rebuilding cheap oscilloscope tubes such as 3PB1, 5BP1 of which there are still ample Mil supplies dating back to WWII.
Rebuilding these screens with P4 (B&W) phosphors would certainly make Pilot TV-37 owners happy.

One last piece of news about RACS: they are hoping for a Navy order of Radar/Sonar rebuilds. This would allow them to reactivate the screen coating line. As it hasn't been used in over 6 months, the entire plumbing must be flushed in formaldehyde and re-brought up to the stringents specs needed to ensure contaminant-free screen deposition.

"It's a very brave venture. I wish all of you every succcess in keeping the craft alive."

Thank you! we will need every help we can get.

Best Regards

jhalphen
Paris/France

Jerome, thanks again for a comprehensive reply. I think the meaning of the word "glassblowing" may have suffered in translation. Here in the UK it means a wide range of skills for working with glass, not just the actual blowing of a glass vessel. So fusing a new CRT neck on to the cone, sealing the pinch etc are all glassblowing. So is making a graded seal, though this requires much more skill.

I agree with you totally about not trying to make Pyrex CRTs from scratch. If you're going to attempt this you might as well make life easier by using soft glass. The cost of the moulds is a big problem if you only need a few CRTs.

A question about h/k assemblies. In the UK VRAT forum http://vintagetvandradio.myfreeforum.org/index.php the point was made that CRT cathodes emit from the end of the cathode cylinder but valve cathodes emit from the main body. This would make valve h/k assemblies unsuitable for CRTs. Do you know anyting about this?

'Valve' cathodes are completely different than those used in a CRT.

Regarding h/k assemblies for rebuilding old guns, it appears they are in very limited supply. Does anyone know if it might be possible to use h/k's from modern CRTs? It has been pointed out that there are guns available for modern tubes but nobody has any use for them. Would it be possible to remove the heater/cathodes from these guns and mount them in place of expired ones on vintage guns? I realize this is a long shot, but it never hurts to toss out an idea. Worst thing that happens if everyone laughs at the dumb guy, right?
Another thought, what about getting guns from Asia? I understand someone is still making CRTs for use in some parts of the world. Maybe a they could make a supply of guns for our old B&W tubes. (I know..probably even dumber, and expensive idea)

When you let a CRT down to air the cathode's emissive surface is wrecked. A new cathode is coated with (I think) a carbonate whch is converted to an oxide during pumping using an RF heater. I'm sure somebody will correct me if I'm wrong.

I don't think it would be feasible to transfer a cathode from one CRT to another entirely in vacuo.

I believe you are correct, it is activated once all the vacuuming getting and baking is done.

Yes, that is correct, but if you are starting with a cathode taken from a new gun intended for a modern tube, then the cathode should still be unactivated, as the gun was never sealed into a tube. The activation of the cathode takes place while the tube is being pumped down, so that the liberated gases can be removed from the tube. The getter is fired once the tube is sealed off from the pump.

It seems highly unlikely that a modern cathode assembly would mechanically fit the older guns, though. The cathode/grid spacing is highly critical for proper cutoff, with tolerances measured in thousandths of an inch.

Activating the cathode after pinch off won't poison the tube, I suspect they were activated during bake out to save processing time.

As I understand it, there are 2 distinct processes: "Breakdown" is done on the pump station and is achieved by ramping up the heater voltage to remove the binder used when the Barium Carbonate material is sprayed onto the Nickel cathode surface, as well as Carbon Monoxide from the Carbonate. Both heater voltage *and* RF induction heating are involved in this process. "Activation" , the second process is done after the tube is sealed off and the getter is flashed, and involves ramping up the heater voltage *and* drawing current from the cathode, to create stable emission sites on the very surface of the cathode. After current is drawn for some length of time, the heater voltage is brought down to "normal" voltage, and operated there for a while, a "slump test" may be performed to determine the stability of the cathode emission.
jr

Not sure about the terminology. There are certainly 2 steps, one during pumping, the other afterwards.

During pumping the cothode is heated with the RF coil (didn't think the heater was needed too but I could be wrong) and the carbonate is converted to oxide. I would imagine this is best done before the tube is sealed off because it liberates some gases.

After it's sealed off and cooled down then you draw current from the cathode to increase and stabilise the emission. For the EMI 6/6 that was rebuilt in 1986 I did this for my first and, so far, only time. I had no idea what sort of voltages and currents to use so I erred on the side of caution. The result was that the initial image on the rebuilt CRT was disappointing. After a couple of hours running in the set the picture improved hugely, to the best and brightest that I have ever seen from one of these CRTs.

Cathodes also seem to get "tired" from long periods of non-use. Again a few hours running usually improves things

Well here is one hard datapoint. A used-but-tests-good 10FP4 just sold on eBay for $227.75.

-Matthew

One thing: If RACS has guns for the specific early 80's color CRTs like the M48AAW00X, 19VJTP22, and the 19VLUP22 used in color XY (and a few raster) arcade games could be a potential source of income for the project. I'd think these being "modern" should mean that they're able to be done with a high yield.

I've been searching for new or good M48AAW00X's for a long time -its limited use (high resolution) makes it difficult to replace. The 19VLUP22 is hard to sub because of its 100 degree deflection angle.

Hello ColorFixer,

I've queried RACS about their having in stock new ready to mount guns for the 3 CRT references you quote in your message.

Will post reply when i get one.

I have also queried them about what equipment/glass/parts they may recycle soon - planned date given months ago was July 2013. Have requested detailed itemized list and prices.

Best Regards
jhalphen
Paris/France