View Full Version : CRT rebuilding as hobby?


CaryLee
02-17-2014, 10:46 AM
Reading that old thread about "new" 16AP4's from France, and the fact that RACS in France is already gone, got me thinking.

I don't understand the first thing about how vacuum tubes actually work, and I understand that rebuilding CRT's requires specialized equipment, but when one thinks that it's actually pretty old tech as far as tech goes, and you look at photos of how the folks on the factory floor building CRT's were wearing semi-formal clothes (slacks and button-up collared shirts), no safety gear to speak of except maybe some gloves, and there was fire and melting glass around, not to mention chemicals, etc. Heck, in the following photo of the guy building the DuMont 30 inch tube I can't tell for sure if he's even wearing safety glasses (He must be)...but it sure looks like he's wearing a tie!


And when you figure that every major city, and a lot of smaller ones, had tube rebuilding shops "back in the day" in all sorts of buildings, with all sorts of folks with different levels of education and experience working there, with all sorts of equipment, it really makes me wonder...exactly how difficult is it to rebuild a CRT? I mean, from a purely mechanical aspect. Granted, working with fire, glass, chemicals, etc. can be dangerous...but would it be any more dangerous than some of the other hobbies out there? There are already hobbyists who are blowing glass, working with chemicals, firing ceramics, soldiering stained glass panels, cutting stone, smelting metals for jewelry or bullet making, working with a shop full of bench top and floor model drills, saws, planers, routers, etc. (I've got a shed FULL of those!) that can cut you up or chew you up. Would rebuilding a CRT be any more dangerous than that?

I'm not talking production, or making a living off it here. I'm just throwing out the idea that someone could take their time, go slow, learn as you go, and take a totally dead hulk and maybe come up with a pretty good rebuilt CRT at the end. No one expects to make a huge profit, or any profit at all, off their hobby when they put hours and hours and hours into a set just for the personal satisfaction of it. (I figure, starting from scratch knowing absolutely nothing about restoring TV's, including study, reading, forum time, finding parts, along with the actual physical work I've done, I've probably got 100 hours or better into my DuMont, and I STILL don't know much about how they actually work.) But I didn't have to INVENT the TV, I just had to repair/replace what was already there.

There's a thread over on the Antique Radio Forum where a fellow is actually building his own vacuum tubes, which I find absolutely fascinating. I mean, if someone can do that in the kitchen or home shop, with glass tubing and surplus equipment, is it really unfeasible to think that a hobbyist, with enough time, money, knowledge, and practice, wouldn't be able to rebuild a 50 year old CRT?

http://antiqueradios.com/forums/viewtopic.php?f=2&t=240669&hilit=make+vacuum+tube

I'm just throwing this out there for conversation basically. It seems pretty much all technology started in someone's garage somewhere, and CRT's do seem to be the major stumbling block to restoration.

Steve McVoy
02-17-2014, 10:53 AM
When we finish the CRT rebuilding facility at the museum we may make it available to people who want to experiment with rebuilding tubes.

old_coot88
02-17-2014, 02:05 PM
Having dealt with many, many rebuilt (re-gunned actually) CRTs back in the day, the biggest problem was contamination resulting in internal arcing. This was true of premium rebuilds and particularly true of 'garage' rebuilds from the guy up the street. I suspect many rebuilds had inadequate vacuum, as they tended to lose emission inordinately fast.

A genuine rebuild would entail re-phosphering as well as re-gunning. I don't recall ever encountering a 'genuine'.

Electronic M
02-17-2014, 04:16 PM
I've often contemplated just that. If I had a few thousand to blow(and a car and a CT-100, and a 40's jukebox so as not have those as a purchasing priority) , that project would be at the top of my to do list.

I feel it would be highly feasible if one had metal fabrication experience (to make your own rebuilding equip), glass working experience, a few duds to play with, and a proper vacuum pump...I feel the rest could be acquired easily and or researched and self taught. A 3D scanner and metal printer could make new gun parts a snap, and this technology is becoming cheaper and closer to a consumer product at an impressive rate.

If I had a few grand to play with, no college or work to take my time (and other expensive to-dos knocked off) I bet I could make a rebuild happen from nothing within two years....With their resources, if the ETF had a clever person with time (enough to make it a full-time endevor), money, and a gung-ho attitude I'm sure they could be having full test rebuilds before fall.

Coot: A full rebuild as you define it is only possible for monochrome CRTs (and only a necessity for pre-aluminized CRTs). Color tubes have a phosphor deposition and shadow mask construction and alignment process so complex that it would be about as much work to make a new CRT from scratch as it would be to re-phosphor one. That is why color rebuilds were gun and safety glass swap only procedures back when rebuilds were an industry.

Steve McVoy
02-17-2014, 04:18 PM
Most tubes can be rebuilt successfully without re-phosphoring. Hawkeye produced high quality rebuilds while they were in business.

In some cases re-phosphoring is required. For instance, here we had some radar tubes (with P7 phosphors) rebuilt for TV use:

http://www.earlytelevision.org/12ap4_substitute.html

Tubejunke
02-17-2014, 10:48 PM
Mr Lee's idea to me sounds great and I hope that anyone who has the capital to run a non profit C.R.T. rebuilding facility has the best of luck with the builds. Now Electronic M looks at it more from the challenge of the build and the mufti-faceted craftsmanship and education that would be necessary with the realization of the need for, well, to be frank; money to throw away.

I tend to just see the reality that such an operation would involve a ton or overhead. And this overhead in the form of skilled (again mufti-faceted) labor would first be hard to find. I don't see this or any operation to be a one man deal. The individual for even close to that would almost need to be formerly trained in electronics, glass work, and metal work or fabrication, and ideally have some years of experience either building or rebuilding vacuum tubes.

So, it would be hard to shoot the original dream of such a hobby down. I'm sure you will have plenty of customers; initially at least. Most definitely it would just be a labor of love and I'm glad that there are still minds out there like MR Lee that just want to do a good thing for no real reason other than the interest and/or helping people. The thought process is to me reminiscent to that which many young people had back in the late 60s

CaryLee
02-18-2014, 06:59 AM
Mr Lee's idea to me sounds great and I hope that anyone who has the capital to run a non profit C.R.T. rebuilding facility has the best of luck with the builds. Now Electronic M looks at it more from the challenge of the build and the mufti-faceted craftsmanship and education that would be necessary with the realization of the need for, well, to be frank; money to throw away.

I tend to just see the reality that such an operation would involve a ton or overhead. And this overhead in the form of skilled (again mufti-faceted) labor would first be hard to find. I don't see this or any operation to be a one man deal. The individual for even close to that would almost need to be formerly trained in electronics, glass work, and metal work or fabrication, and ideally have some years of experience either building or rebuilding vacuum tubes.

So, it would be hard to shoot the original dream of such a hobby down. I'm sure you will have plenty of customers; initially at least. Most definitely it would just be a labor of love and I'm glad that there are still minds out there like MR Lee that just want to do a good thing for no real reason other than the interest and/or helping people. The thought process is to me reminiscent to that which many young people had back in the late 60s


A young person back in the 60's? Really? I'm 50 years old..too young to have been a "young person" back in the 60's. Well, I was born in '64, so if you are talking about being 5 in 1969, then "guilty as charged". I credit my thinking with a thought process more along the lines of that which I acquired from my grandfather, who was a "young person" during the depression and had to learn to do for himself with what was on hand. The same guy who got home from the Navy after WW2 only to find shortages which kept him from buying lumber, so went to a dump and salvaged crates from aircraft wings for wood in order to build an entire two-car garage. The same guy who once got a flat, by himself, on some lonely desert road in the 1960's only to find someone had stolen the jack from his flatbed truck, so searched the desert for a couple hours, gathering up enough stuff to make a lever out of scrap laying around to lift the truck, keep it lifted, and change the tire. The same guy who I was traveling with when the alternator quit on his pickup during the middle of the night in Nevada, so we drove on for a hundred miles with the lights shut off and me sticking a flashlight out the window, shining it on the white line on the side of the road, passing one other car the whole time. And then, when the battery was too dead to run the engine, we slept in the cab with our feet sticking out our respective passenger windows until daylight, and then finding ourselves on a slight incline where we could walk beside the truck leaning on it to get it to roll, we pushed..yes pushed.. the 1971 Ford 3/4 ton that last 10 miles into Needles, California, down the offramp, and coasted right up to the service bay of an auto repair shop we didn't even know was there. I could tell dozens more such stories after spending years working with him and just hanging out with him. He was the kind of guy who didn't know he wasn't able to do anything, so he just went and did it. I hope I'm half the man he was.

One question: Does everyone who, as a hobbyist, restores old radios or TV's have an entire furniture/cabinet shop and electronics manufacturing facility tucked away somewhere in their home? Have they all been able to turn their hobby into profitable business ventures with all that demand for ancient B&W sets and AM/Shortwave radios out there? Lucky them! I'm beginning to see this all in a new light! :)

I wasn't talking about having to turn a profit from this by having to rebuild hundreds of CRT's. I was talking about the feasibility of doing it oneself simply as a hobbyist. I've spent perhaps 100 hours between research and actual work getting my DuMont going. Most likely a lot longer than it took to originally build the set. And I still know very little about HOW it works..but it does work. And yes, it was a labor of love that wouldn't have ever gotten done otherwise. I don't believe I will ever recoup my investment in either time or money. I also restored/repaired a 1921 Brunswick wind-up phonograph and a 1938 RCA Console radio last year. Neither of which I'd ever laid eyes on before, let alone knew a thing about working on. They are both daily players today, but I doubt I could make any money off either of them.

How many of us knew everything there is to know about something before we actually tried it?

Obviously, taking apart the tube isn't the main issue. That can be done, after proper evacuation of the vacuum, with $50 worth of special hand tools. Or a $6 dollar glass cutter if your really good or not particularly concerned with the potential failure rate if you don't get it right in one scribe. It's what comes after that's the big deal.

Just for the sake of conversation, here's something interesting where someone is actually making their own simple CRT's:

http://www.sparkbangbuzz.com/crt/crt6.htm

Steve McVoy
02-18-2014, 07:26 AM
In addition to the facility we are setting up at the museum, there are two collectorss who are pursuing rebuilding their tubes. One is setting up one of "garage" plants:

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

The other is rebuilding a 15GP22 in a way that he hopes will solve the leakage problem these tubes have:

http://www.earlytelevision.org/yurkon_15g_project.html

CaryLee
02-18-2014, 11:46 AM
In addition to the facility we are setting up at the museum, there are two collectorss who are pursuing rebuilding their tubes. One is setting up one of "garage" plants:

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

The other is rebuilding a 15GP22 in a way that he hopes will solve the leakage problem these tubes have:

http://www.earlytelevision.org/yurkon_15g_project.html

Very interesting!

That "garage plant" idea is something I'd never heard of before...but it does make sense and is right on track with what I was thinking. I remember reading old copies of Popular Mechanix and Popular Science back when I was a kid..which meant the mags were probably from the 50's and early 60's, and it seemed people, coming out of WW2 and heading into the days of the moon landing, were willing to try doing everything and anything for themselves..from smelting metal to building their own ham radios to building their own flying cars, stuff that hardly anyone attempts today. Who knows how much of it actually got done at home, but the ideas were out there. It's been that kind of "we can do it" thinking that's always fascinated me.

Now the re-engineering of the 15GP22 looks WAY beyond the scope of a "simple" rebuild! Reading that write-up is absolutely mind-blowing to me. MAJOR kudos for even attempting that project!

Thank you for posting those links. I'm very interested in what you folks are doing at the museum. Other than hauling around my grandparents DuMont for 20 years and finally getting it operating again over the last couple of months, I'm really a complete "noob" to all of this, but I've always been willing to try anything once.

CaryLee
02-18-2014, 11:52 AM
Having dealt with many, many rebuilt (re-gunned actually) CRTs back in the day, the biggest problem was contamination resulting in internal arcing. This was true of premium rebuilds and particularly true of 'garage' rebuilds from the guy up the street. I suspect many rebuilds had inadequate vacuum, as they tended to lose emission inordinately fast.

A genuine rebuild would entail re-phosphering as well as re-gunning. I don't recall ever encountering a 'genuine'.

Do you figure it was simple contamination by a leaking seal? Or would there be particles left inside the CRT even after air evacuation that might interfere with operation? I would imagine that the biggest hurdles to rebuild would be a clean environment, and resealing the tube. Out here in dusty and windy northwest New Mexico, we have a hard time keeping dirt out of anything.

bandersen
02-18-2014, 12:49 PM
Another hurdle is finding a new electron gun assembly to put in the CRT. They're no longer made AFAIK.

old_coot88
02-18-2014, 01:55 PM
Do you figure it was simple contamination by a leaking seal? Or would there be particles left inside the CRT even after air evacuation that might interfere with operation?
it had to be particulate contamination, i.e., dust etc. that caused the internal arcing.
Rebuilds arcing was such a problem that the Boss got a tool we called the 'Cattle Prod' which became standard equipment for 'cleaning' every rebuild prior to installation. It was a hand-held, AC-operated high voltage probe that put out probably 35 KV or so of AC. You'd apply the "business end" of the Prod to the CRT base pins, and any loose particles inside would incandesce white and fly around until they all 'stuck' somewhere and all the sparking ceased.

In retrospect, i sometimes wonder if this procedure might've liberated gas that could have contaminated the vacuum.

I would imagine that the biggest hurdles to rebuild would be a clean environment, and resealing the tube. Out here in dusty and windy northwest New Mexico, we have a hard time keeping dirt out of anything.
Yep, cleanliness is everything insofar as rebuilding CRTs.

And i still think the more correct term should be re-gunning rather than rebuilding.

miniman82
02-18-2014, 05:49 PM
Insofar as 'shadetree' tube rebuilding is concerned, yes it is possible. What needs to be understood by all is the need for a dedicated processing facility, having all the necessary tools on hand in order to do the work correctly. Please understand: it's not just a simple matter to plugging a new gun in and evacuating the tube- it's much more involved. Having done tube rebuilding myself in France, I think I have a unique perspective on this subject.

Here are some of the items you will need in your rebuilding quest:

neck cutting apparatus (hot wire tool)
Vertical or horizontal lathe
New/rebuilt guns on hand
Oven, with pumping gear (roughing pump and diffusion pump)
Timer, to control the oven
Cooling rack
Spark knocker
RF bomber (getter flashing)
Cathode activation station
Aging rack (to condition the tube prior to service)
Dag application station
Final test apparatus


Admittedly there are a few items that could be skipped or omitted entirely, but the quality of the end product depends entirely on the systems used to build said tube and the acumen of the individual doing the work. All this being said, it's my opinion that a high quality vacuum tube cannot in this day and age be produced in one's garage. It takes years of skill and many thousands of dollars worth of specialized equipment in order to do the job correctly. And I haven't even scratched the surface of what it takes to do a phosphor job...

Not to dissuade you from trying, but the right people are already working on this as I type. I'm one of the people involved (eventually) in the rebuilding effort already underway at ETF. I think if it's going to happen at all, ETF is the place where it will happen. If you want to make a difference, please consider a generous donation to the project. Any money collected will only help further the efforts already underway, though there is no promise of success in this venture. I hope to one day be parked in front of a lathe to help you all, but unless we pull together it is not likely to become a reality for anyone. That said, efforts to try and do it alone in my mind represent time and money that could be focused on the ETF project. We need to be selfless in our dedication here- it's a very ambitious goal, but it's also just waiting to happen if we dig in and get it done!

snelson903
02-18-2014, 06:42 PM
off hand how many inch's of vacuum are crt's vac down too, 29-30 for moister removal like a/c units are ?

Username1
02-18-2014, 07:01 PM
much more than A/C equipment. 400 microns is very good for a/c....
Now imagine maybe 1000 times that....
baking to near the melting point of the glass to remove more than moisture,
but to remove other chemical contaminants.

A simple way of looking at it, is that the more molecules of "air" removed, the less obstructions there are in the path of electrons to flow to the screen, any obstructions reduce screen brightness..... In addition to this, contaminants eventually "poison" the cathode, and reduce it's ability to release electrons to shoot at the screen....

Not quite the same requirements for a good a/c system to work, even though they are both vaccum'd, but to achieve slightly different results.

miniman82
02-18-2014, 07:17 PM
Not even in the same universe...

snelson903
02-18-2014, 07:53 PM
anyone know the number though ?

jr_tech
02-18-2014, 08:02 PM
Something like 10 to the -6 to 10 to the -7 mm of mercury would be a decent seal-off pressure for a CRT.
jr

snelson903
02-18-2014, 08:09 PM
thats what im looking for, thanks jr tech

CaryLee
02-18-2014, 08:35 PM
Looks like there's been some recent rumblings in the UK on this subject as well. Seems the gears are turning in quite a few brain pans around the world...

http://www.forum.radios-tv.co.uk/viewtopic.php?f=15&t=7203

Einar72
02-18-2014, 08:57 PM
Steve, I have (somewhere) internet pictures of new production 12AP4-like tubes from a decade ago, made by Thomson before they ditched RCA operations. Any idea who they were for? I believe the photos were taken in a restorer's home.

[QUOTE=Steve McVoy;3095978] Most tubes can be rebuilt successfully without re-phosphoring. Hawkeye produced high quality rebuilds while they were in business.

In some cases re-phosphoring is required. For instance, here we had some radar tubes (with P7 phosphors) rebuilt for TV use:

dtvmcdonald
02-18-2014, 09:25 PM
Ideally you want 1.e-6 (one millionth) torr.
A torr is 1/760 atmosphere. For ordinary tubes
1.e-4 torr is not "gassy" but a CRT would not like that.
1.e-2 torr of air will give a nice purple glow,
not bright but there.

The pumps used in processing will easily do 1.e-6 torr
at their inlets ... but its not easy to get that through the glass stem.

Telecruiser
02-22-2014, 11:01 PM
I think the glass and vacuum part would be easy compared to getting new guns. Does a source still exist? Probably in China if it does....

StellarTV
02-23-2014, 12:30 AM
I have a strong interest in learning the rebuilding trade... if I could find the equipment would have no problem setting it up to to learn how to do it. I find it extremely fascinating!

Tom Albrecht
02-23-2014, 02:11 AM
Justin, keep your eyes on eBay. Rebuliding equipment comes up from time to time. I've also thought about trying to resurrect a rebuilding system some day, but turned down an opportunity to buy some equipment locally 5 or 10 years ago. I have some knowledge and experience with high vacuum and ultrahigh vacuum systems, and would happy to help with advice,troubleshooting, etc., if you find some equipment and decide to set it up at your place.

I have no idea how hard it is to find replacement guns, however.

snelson903
02-23-2014, 02:26 AM
I have a strong interest in learning the rebuilding trade... if I could find the equipment would have no problem setting it up to to learn how to do it. I find it extremely fascinating!

im with you Steller, if back in the day the larger tv repair shop's had there own equitment for doing this, even if its just for black & white tubes maybe its still out there and manuals for it. and getting the equitment to vacuum it down is easy to come by ,any automotive a/c vacuum pump will 29.92'' hg or even a used refrigerator compressor will vac down to 29.92"hg =760 torr at 0 sea level .witch is more than enough .

Steve McVoy
02-23-2014, 09:22 AM
Einar72, we had those tubes made for collectors:

http://www.earlytelevision.org/12ap4_substitute.html

As for the availability of guns, ones for the old tubes are no longer being made. There are an unknown quantity out there - from shut down rebuilding facilities. We have been able to purchase some of them.

The other approach is to use the old gun and replace the cathode and heater, both of which are still being made, but for how long no one knows. We are attempting to buy a stock of these.

jr_tech
02-23-2014, 11:03 AM
getting the equitment to vacuum it down is easy to come by ,any automotive a/c vacuum pump will 29.92'' hg or even a used refrigerator compressor will vac down to 29.92"hg =760 torr at 0 sea level .witch is more than enough .

Not even close... read my post above, it is difficult to express exponentials on this site. When I wrote 10 to the -6 mm of Hg, this. means 1 millionth of of a torr:

"One millionth is equal to 0.000 001, or 1 x 10−6 in scientific notation. It is the
reciprocal of a million, can be also written as 1/1 000 000. Units using this fraction"

jr

snelson903
02-23-2014, 12:33 PM
Not even close... read my post above, it is difficult to express exponentials on this site. When I wrote 10 to the -6 mm of Hg, this. means 1 millionth of of a torr:

"One millionth is equal to 0.000 001, or 1 x 10−6 in scientific notation. It is the
reciprocal of a million, can be also written as 1/1 000 000. Units using this fraction"

jr

heres i hope a chart i found, when i was in G.M. or oldsmobile a/c training yrs back to remove all moister from desacent we had to boil cold water at-30inch or 29.92 of vacuum thats alot more than it sounds the chart i found puts 760 torr on the same scale as 29.92 if its not what in inch are crt vacuum down too . there's some interesting video's on youtube of rail cars emploding with low vacuum, type in [ rails cars emploding ]

jr_tech
02-23-2014, 01:31 PM
Nice chart, Again 10 to the -6 is about what is needed to process a CRT, and simply put you can't get there with a simple mechanical pump such as those used to pump refrigeration systems. Most CRT processing stations use a diffusion pump, sometimes with a Ln2 cold trap.
Now the mechanical gauge on such a system *may indicate* a "perfect vacuum", but really it is not capable of making a precise measurement. It would sort of like trying to measure the speed of light with a stopwatch! A decent ion gauge is needed to measure high vacuum, *not* a barometer type mechanical gauge.
jr

Ion Gauge : http://en.wikipedia.org/wiki/Hot-filament_ionization_gauge
Diffusion pump: http://en.wikipedia.org/wiki/Diffusion_pump

snelson903
02-23-2014, 02:09 PM
after seeing the other types of vacuum pumps , i didnt know they could go that low to remove more than moister.

bandersen
02-23-2014, 02:17 PM
10-6 torr is about 0.00000004 inches of Hg

WA3WLJ
02-24-2014, 01:10 AM
Water boils at about 12 Torr at 74 Degrees F

WA3WLJ
02-24-2014, 01:14 AM
Diffusion pumps get down to 5 X 10-8 or better at work , which is 200 times better than 1 X 10-6

StellarTV
02-27-2014, 01:00 AM
Justin, keep your eyes on eBay. Rebuliding equipment comes up from time to time. I've also thought about trying to resurrect a rebuilding system some day, but turned down an opportunity to buy some equipment locally 5 or 10 years ago. I have some knowledge and experience with high vacuum and ultrahigh vacuum systems, and would happy to help with advice,troubleshooting, etc., if you find some equipment and decide to set it up at your place.

I have no idea how hard it is to find replacement guns, however.

Will do. I know a couple of scrappers in the LA area that will let me know if any of that equipment comes through... but I'd MUCH rather find something local. Don't want to think about the logistics of moving all that stuff over such a long distance but you never know...

Be happy to work with you if and when the time comes. :) Likewise, if somehow you pick up something, let me know!