I plan to post periodic reports on our progress here.

First, I'd like to say that we view this as a long term effort - probably years before we can produce rebuilt tubes in any quantity. And, of course, we may never get there.

Our goal is to have a non-profit, self supporting operation that rebuilds tubes for collectors.

We have been making slow but steady progress toward this goal. First, we got the equipment from Hawkeye when they shut down and transported it to Hilliard. This gave us most of what we need to rebuild tubes.

This year we built the room where the equipment will he housed. Volunteers at our convention completed the drywall finishing, and the equipment will be moved in soon.

Recently we raised $8,500 to purchase and ship to Ohio phosphoring and aluminizing equipment from RACS. It should arrive this summer.

We have been accumulating stock of guns, glass, etc. as we find it. I think there is a considerable amount of this stuff out there that we will eventually get.

Our hope is that this year people will use the facility to experiment with rebuilding.

We also hope that by next year we will have a funtioning, active committee in place to oversee the operation. This group would work on the problems:

1. A business plan. Which tubes can we rebuild at a price that collectors can afford? How do we manage the facility?

2. How do we deal with the long term problem of guns? We will have a sufficient stock to do some tubes (who know how many, but maybe 100 late 40s black and white tubes and 50 color roundies), but we will need to find guns, stems, glass tubing, getters, etc. for an ongoing operation.

Very cool, thanks for the update !

Stems and guns: I found this on E3ay this afternoon. The vendor states they have many in stock. Looks like a color gun.

http://www.ebay.com/itm/Steam-Punk-Art-CRT-Tube-Gun-/351012932248?pt=LH_DefaultDomain_0&hash=item51ba004a98

Can an inline color gun like that even be a good parts donor for the monochrome and delta-gun color types that are worth the effort to rebuild?

At one time, the discussion turned to trying to broaden the types of tubes that could be rebuilt. If they posted an inline gun, and they stated that they have others, there could be delta and monochrome guns in the stash as well.

A tube like M48AAW00X is an example that is popular and priced high enough to warrant a rebuild attempt for those who need them.

Progress Report, July 12, 2014:

Walls and ceiling of the CRT rebuilding room have been painted. Next is the floor. We will schedule a day sometime this summer for volunteers to install the equipment and finish the construction.

We are still waiting for details of a quote that RACS received for shipment of their stuff to Ohio. We expect that shipment will happen this summer.

I can't wait until this happens.. I'm going to put a tube aside to wait and have rebuilt..

Progress report - September 8, 2014

www.earlytelevision.org/crt_project.html

Steve-

I am very happy to hear of the progress at the ETF. If I was nearby, I would want to help with the museum/foundation's efforts. Thank you for the ongoing work and for posting the update.

Take a look at our project page. We have made a great deal of progress:

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

That is great.

Thank you for the update and the pictures.

super! Thanks for the updates.

Very good to see the Oven coming together. Has a decision been made as to a make/model of thermostat and if it will just have one temperature probe or multiple?

Is the sheet metal uncoated or is there a coating on it that might out gas when heat is applied?

Matt

This is the controller we are going to use:

http://www.amazon.com/JLD634-Setpoint-Temperature-Controller-FURNACE/dp/B004HHW2P8/ref=sr_1_1?ie=UTF8&qid=1409506415&sr=8-1&keywords=ramp+and+soak+controller

There will be a single temperature probe. I think the convection fan will keep the temperature uniform.

The sheet metal is galvanized. I'm sure there will be plenty of nasty fumes when I first fire it up - oil, etc. and probably something from the insulation. Over a few hours it will probably all be burned off. During the tube baking it doesn't matter because the inside of the tube is sealed via the O ring on the diffusion pump.

This is the controller we are going to use:

http://www.amazon.com/JLD634-Setpoint-Temperature-Controller-FURNACE/dp/B004HHW2P8/ref=sr_1_1?ie=UTF8&qid=1409506415&sr=8-1&keywords=ramp+and+soak+controller

There will be a single temperature probe. I think the convection fan will keep the temperature uniform.

The sheet metal is galvanized. I'm sure there will be plenty of nasty fumes when I first fire it up - oil, etc. and probably something from the insulation. Over a few hours it will probably all be burned off. During the tube baking it doesn't matter because the inside of the tube is sealed via the O ring on the diffusion pump.

How hot is the target temperature in the chamber during bake-out?

775 degrees F

That could be an issue. "Galvanized steel is suitable for high-temperature applications of up to 392 °F (200 °C). The use of galvanized steel at temperatures above this will result in peeling of the zinc at the inter metallic layer."

Oops. I should have checked that. I assume that means that the steel is still structurally OK, just that the galvanized coating will separate. If that is true there isn't a problem. It will just look bad and maybe rust.

Zinc oxide - Iron oxide - not a problem ? Stuff flaking off into an environment
where extreme steps are being taken to keep from poisoning a new cathode....
Not a problem....?

Remember that the CRT is completely sealed when it goes in the oven. The only opening is the stem, which goes into the diffusion pump and is sealed with an O ring. Any contaminants that are in the oven never get into the tube, where the gun is.

I don't think the nickel coating, or potential rust, will be a problem.

OK,

I am sure it will smell lovely during the first few times of operation :)

I like that temperature controller, I would personally also opt for the 25A solid state relay since the internal relay is only a 3A.

Just my $0.02

Matt

OK,

I am sure it will smell lovely during the first few times of operation :)

I like that temperature controller, I would personally also opt for the 25A solid state relay since the internal relay is only a 3A.

Just my $0.02

Matt


Bob beat me to the punch on the Zinc issue...(Actually I went to bed after posting.) But he was thinking along the same lines.

Just a heads up, you do NOT want to inhale zinc fumes. https://en.wikipedia.org/wiki/Metal_fume_fever

Mild or Stainless. The choice depends on if you can live with rust and/or have the budget for stainless...

Your target temperature is just high enough that you wouldn't catch me in the same enclosed space without an apparatus for breathing.


Squirrel Boy also helpfully points out that anything hot and galvanized around virgin cathodes is a very bad idea. The vapor *will* travel, and produce fine granules of zinc, which *will* get into/onto everything. If you want a practical demo, just break open a bottle of laser toner in the rebuild lab. You'll be finding it everywhere for MONTHS afterwards no matter how carefully you think you managed to clean it up.

I was not going to say this, but I do believe that at that temperature
zinc would be a bad idea. Its probably not a health risk, but would be at
100 degrees hotter.

I would break down and change to 300 series stainless steel. For
a system that small it does not have to be thick.

This is advice from a person who has done tons (literally!)
of vacuum stuff involving electronics and heat.
At that temperature even stainless will be strongly oxidized and
turn brown, but it will not flake.

In many cases of even slightly larger ovens than yours brick
is normally used, but since you already have it, go to stainless.


Doug McDonald

I asked a friend of mine at MIT who works with high vacuum systems as part of his research on nuclear fusion. He strongly agrees with the prevailing opinion that zinc in the rebuilding room is a bad idea:

Well, it looks like the zinc itself is not vacuum-facing, just in the oven surrounding the tube which is being pumped on. The bigger issue is what was already raised in the thread — the zinc melting off and potentially putting nasty vapor in the air and otherwise putting zinc flakes everywhere.

That being said, zinc inside the vacuum is such a bad idea even Wikipedia has a comment on it:
http://en.wikipedia.org/wiki/Materials_for_use_in_vacuum
Notably, the zinc will almost certainly sublimate at your temperatures/pressures and can leave conductive deposits in places you probably don’t want them.

See also NASA’s regulation on zinc in vacuum for a more technical/authoritative source:
http://nepp.nasa.gov/npsl/Prohibited/zinc_prohibition.htm
Also prohibited are cadmium and (pure) tin:
http://nepp.nasa.gov/npsl/Prohibited/index.htm

This alone may be sufficient reason to keep the zinc flake from being produced in an environment where you are working on tubes — even if it weren’t direct threat in the oven itself, you probably don’t want it floating around your nominally clean workspace and getting into other tubes.



I am happy to chip in to help pay for the cost of stainless and strongly suggest that we should go ahead and replace the galvanized.

-Matthew

Thanks for your comments. I think I'll fire it up and run it for several hours (It is in a large warehouse - I'll do it when there are no people in the room and have good ventilation) and see what happens. If there appears to be an issue I'll go the stainless route.

Matt, I've ordered a 40 amp solid state relay and heat sink. The heating element is 8400 watts.

You know the zinc doesn't just flake off nice and neat, it powders off and it does make
extra stinky nasty gases..... Why risk getting that crap all over the building....?
That little fan in there, you gunna run that on yer test....?

And no laser printers in that building either......

Thanks for your comments. I think I'll fire it up and run it for several hours (It is in a large warehouse - I'll do it when there are no people in the room and have good ventilation) and see what happens. If there appears to be an issue I'll go the stainless route.

Matt, I've ordered a 40 amp solid state relay and heat sink. The heating element is 8400 watts.

Please, think about things before proceeding. Getting zinc everywhere is not a good idea. It could damage things in the museum. (Do you want metal powder settling on open-bobbin flybacks?) Not to mention the whole "Well we have a 30% failure rate on rebuilds after 100 hours of use and we can't figure out why?" issue of poisoned cathodes that awaits.

If you're not willing to take 7jp4-guy's offer of financial assistance to change up to stainless, at least consider buying a $16 pail of refractory cement at the hardware store and 'spackling' the entire exposed galvanized inside with a thin coating to minimize the zinc exodus. As a bonus this will add a bit more thermal insulation to the whole apparatus, plus because it is white it will reflect more heat back into the oven than metal would and thus increase systemic efficiency, which lowers your cost per tube.


Yes, I'm sure there were many one-man rebuild operations run out of terrifyingly dirty garages and basements. I'm also sure that they produced working rebuilds. What nobody is sure of is what the lifespan of these mom-n-pop back-alley rebuilds was compared to say an NVC rebuild. If people are going to pay you to rebuild a tube, I think they're hoping (like me) to get a rebuild that exceeds all original specs, because we have 60+ years of knowledge, tech, and tools to do the job.


I've refrained from posting the following observation/thought because I wanted to wait for more news from ATF on which way they were leaning toward, but it kind of goes hand-in-hand with the current topic of discussion.

Regarding re-phosphoring or just re-gunning.

If I'm budgeting to have a rare or significant tube rebuilt, much like a car there's things that you just do while you have it torn down because it is cheaper and easier to replace parts that you have easy access to. So if I'm going to have a tube refreshed, I'd feel better about stripping the jug and re-phosphoring and aluminizing. There will come a point where bent-guns are no longer an option, and if you can't aluminize a tube, then all it will be good for once re-gunned is short demos in a dark room or you're just going to wind up with a big goose-egg ion burn up front, and then it's really pooched because there's nobody to re-phosphor it, even if the gun is good for another 8k hours.


The solution to all of this is to determine the haz-mat disposal fee related to the wet-process of re-phosphoring a tube, and declare that up-front to the customers in the same way that you have to pay a haz-mat fee to dispose of tires and automotive fluids. The actual bench process can (and should!) be heavily revised to significantly reduce the volume of haz-mat produced at the increase of labor and/or in non-hazardous alternative consumables.


Specifically, I'm looking at the HFA based stripping process. You can strip the phosphors off with a weaker acid and some mechanical scouring action. (Put the tube on a rotary-shaker table with some water+acid/base and soda-lime marbles or even just a cup of lead-free birdshot for a few hours.) This way you don't produce many many gallons of water+HFA+barium/lanthanum/etc haz-mat like RACS did. You will still produce, say 1.5 gallons of non HFA haz-mat containing just the phosphors and weak acid/base, and then you do the final rinse/clean of the inside with the HFA process only once for the desired surface prep, using significantly less than a quart of acid solution, and probably being able to re-use the same acid two to five more times before it becomes exhausted since it isn't eating up ALL the phosphor and aluminum, it's just putting the final polish on.

We have now potentially reduced the haz-mat disposal requirements by an order of magnitude or more in volume, but we've added some extra processing time via the shaker-table. I'd wager the extra time is cheaper than the bulk haz-mat disposal rate, though.


Hell, I'm pretty sure that 24 ounces of bismuth bird-shot, an inch of warm water, and a pint or maybe 20 fl oz of regular old lye on a shaker-table will strip the face of all aluminum and the phosphor in 60-90 minutes. You'll have to put it on a tilt lathe or roller table to de-aluminize the rest of the bell, but still entirely feasible. Even if someone had to go in and 'bottle-brush' the neck and bell, lye will eat that aluminum right up. (Yes, I know, fumes. I'm pretty sure you're going to have to install a fume hood at some point to comply with OSHA, but that's an infrastructure cost over time, not a consumables cost.) On the up-side, the effluent produced is low-grade hazmat, only because of the phosphor compounds. The lye is just "caustic" and you can neutralize that on-site rather cheaply. I'm also fairly sure that there's a non-hazardous way to strip the dag if that somehow survives the caustic assault.

Again, instead of washing it all off with copious HFA and H2O, you can use something slightly more tame than HFA with a bit of mechanical assistance to do the real dirty work, and only unleash the HFA in a smaller dose to achieve the final ultra-clean surface that is required in re-phosphoring the face.


Go find an undergrad student majoring in inorganic-chemistry at your local edifice of higher education and ask how he(or she!) would solve the problem of cleaning glassware that has phosphor and a few microns of aluminum stuck to it. (CRTs are just very large erlenmeyers when it comes to "I need to clean this filthy thing extremely thoroughly.") Actually, even an org-chem major can provide workable solutions. They have all kinds of fun gloop stuck to their apparatus that they need removed entirely, too! They also probably know more about exactly what waste products are and are not classified as haz-mat these days and can advise the best way to minimize reportable waste while still achieving the necessary final result. They're also happy to be paid in beer, food, or fuel, if not for free just because someone finally asked them to help solve a real world problem with their knowledge even though they don't yet have that shiny degree on the wall. Grads want a budget and a notch on their resume, while post-grad students can only afford to consider problems that have grant-money attached to them. Undergrads aren't fully jaded like that, yet...


You folks at the ETF have come a long way towards the goal of rebuilding CRTs again, but don't scuttle the whole project with an avoidable mistake or by limiting your potential at only providing palliative care with a new gun shining onto old phosphor. If I have a tube that went to air in 1968 because the socket came loose, I really do not trust the phosphor coating to behave properly no matter how much you bake it out. If it was aluminized then it will certainly require the full service process to obtain an acceptable result. In 44 years with access to the atmosphere, those few microns of aluminum have become mostly aluminum oxide with just a tiny bit of actual aluminum underneath. Remember that AlO2 is an electrical insulator, and that alone is enough to result in an inferior finished product. I'd also put good odds on the AlO2 flaking off the face/bell and falling into the gun assembly during pump-down and bake-out, much to the detriment of the finished product from that side of things.

Thanks everyone for your comments. I will replaced the galvanized metal to avoid the zinc issue.

As for re-phospohoring and aluminzing, we have the equipment to do that coming from RACS later this year. We also have a person who visited RACS for two weeks and learned the process. At some point we will deal with the issues of getting this equipment converted to operate on US power standards and with the environmental issues.

The vast majority of the dud tubes out there are still under vacuum, so the existing phosphor is most likely OK.

Bent guns are not available now - we plan to replace the heater and cathode in existing guns.

Well, I think that Steve is working very hard to get a really terrific thing off the ground.
I'm beginning to think that each step, and every little item may need to be looked at by
more people just so something can be avoided like short life tubes after a rebuild. Like
NoPegs said above. Not that Steve and the people at the museum are not doing the best.
But more along the lines, that an overlooked item may mean a hundred tubes will
possibly have a short life due to something no one realized.

I also think that as for the bent guns not being available, the best solution I think is to
rebuild the bent gun, and not mess with a good screen. Re-coating the screen should
only be done after rebuilding bent guns is tried and failed repeatedly.

It's just my thoughts that disturbing something that you are not sure you can replace
with long term reliability should not be jumped on quickly and without long term testing
first.

Username1, thanks for you comment. We are not doing this project without a lot of expert help. Several of our members have participated in rebuilding tubes at Hawkeye and RACS. One of our members spent two weeks in France at RACS learning the process. Scotty at Hawkeye and Phillipe at RACS are available to us to help when we need them. Nothing we are doing is new - guns have been rebuilt before, and the process of rebuilding tubes is well understood and documented. I don't think we will have a problem with tubes having short lives.

I understand you guys are knowledgeable on this, but you were not there to build
the equipment at RACS, or at Hawkeye. You are however, building some new equipment
at your location. What I am saying is that if you don't look into even the smallest
details on the items you use, proper procedures may not make a difference, you could
innocently introduce something unintended and have problems.....

Believe me, I do wish you luck on this project.......

Keep up the good work Steve and I wish you total success! You can count on a tube or two from me when the time comes. If I lived local to you I would be there helping all the way to a finished product.

Gregb

Since the galvanized was not used, what metal is now being used?

I'm using bare steel for now. At some time in the future I may replace it with stainless. The Hawkeye oven was full of bare steel, so i think it will work fine.

Krylon makes a spray-on high temp paint, good to 1200 deg. F. What do you think of spraying the steel with it?

http://www.homedepot.com/p/Rust-Oleum-Specialty-12-oz-Bar-B-Que-Black-Satin-High-Heat-Spray-Paint-7778830/202315061#specifications

Krylon makes a spray-on high temp paint, good to 1200 deg. F. What do you think of spraying the steel with it?

http://www.homedepot.com/p/Rust-Oleum-Specialty-12-oz-Bar-B-Que-Black-Satin-High-Heat-Spray-Paint-7778830/202315061#specifications

Unless you're only planning on firing the oven up during the full moon, I think you're over-thinking things. Blacksmiths don't paint their anvils or tools for the same reason. Once the surface rust happens, it won't progress much further unless it goes unheated for long periods in wet weather. I'd loop back to the "Well, what are the potential side effects if it flakes off or outgasses etc?" line of thought and just go with "Steel."

Untreated steel is the best option. High heat keeps rust from progressing to the
point it will become a problem. And if the oven remains unused for any period of
time, heating it and or wire brushing it down will remove any rust.

You can keep a dehumidifier in the room to keep humidity levels down and
keep the bare steel from forming any oxide from becoming a problem.

I believe in time you guys will have no choice but to rethink how you will rebuild
tubes. And I am thinking the gun, stem, and pinch off will be changed because spare
items will not be available. I think in the future, guns will be rebuilt, and the neck
will have to be rewelded to the old tube envelope at the point that use to be the separate
stem, and the entire oven may need to be under vacuum.... Just thinking about how things
will have to be done when new guns complete with through wires and stem/pinch off's as
a finished assembly are not going to be available.... For that reason, you may well
begin to think about a really clean oven...

.

I am sure they are think about this, this is the first revision of the oven. The reason for the experimentation is that this is retrofitting an existing oven and enlarging it so that very large (30BP4) tubes can be rebuilt with relative ease.

I am glad to be seeing a large amount of progress being made in this effort rather quickly as of recent,

For that reason, you may well
begin to think about a really clean oven...



Lets bootstrap things here and start with a laminar flow hood for the gun reworking process area. Someone keep an eye open on the local used markets and pick one up for a song and store it until needed. The vacuum kiln will come in time...


I'm going to regret saying this, I'm sure...

Hawkeye was a master artisan of tube doctoring, he used tried and true methods and equipment to re-gun tubes with a high rate of success and had a very solid understanding of the fundamental processes involved. RACS were a bit more cavalier about their process, but knew a lot of tricks and reliable methods, especially for Pyrex jugs. However, their bench methods were just a bit on the scary side of things. I shudder to think about the lit cigarette accompanying most of the process.(Both for the quality of the rebuild, and from the ingesting all kinds of fun things aspects.) The communal spoon and weighing pans are also up there on the list of crazy stuff. One spoon per compound, and at least use weighing papers... I understand we're not cloning cell cultures or building a space probe here, but just because RACS got away with their cowboy techniques doesn't mean that following their lead is a good idea. (Props to Nick rocking out his E-cig though!)

Again with the car engine analogies: If my mechanic is pulling the head and sending it out to be rebuilt, I'm expecting him to securely cover the open block while it's out for service. I don't want chunks of cutoff wheel and rusty exhaust clamps flung into my open engine from the next bay over. Obviously it will still start and run, but in time all that crap will take a toll on something important and shorten the life.

Along the lines of cleanliness, should we not also try to have the room at a slight positive air pressure, just like they used to do(and maybe still do) in computer centers. The slight positive pressure helps to keep dust from migrating in.

Username1, I'm not sure what you are getting at. We are already fusing a new piece of glass to the old shell, and we are planning to rebuild the gun, since the supply of guns is very limited. The only materials we need are neck glass, stems, cathodes, heaters, and spacers. Neck glass and stems will never be a problem - there will always be glass fabricators that will do custom jobs. Cathodes and heaters may become problems at some time in the future, but are available now. If it appears that the supplier may stop making them, we will order a large quantity.

So, I don't see any need to ever change our rebuilding method and evacuate the entire oven.

As for cleanliness, Hawkeye was very un-clean, and yet they produced high quality rebuilds. Our facilities and oven will be much cleaner.

Pyrex CRTs present special problems. Apart from the higher temperature needed to work Pyrex it's likely that a soft glass pinch will need to be used. There are no new Pyrex pinches and re-using the old one has been regarded as not feasible. Though I suppose that could change if driven by desperation.

You can't fuse pyrex directly to soft glass as the differing coefficients of expansion will ensure the result will crack. Hence you need a graded seal, with several intermediate grades of glass between the pyrex and soft glass. The special glasses are available but it requires a high level of glassblowing skill to do it. My understanding is that RACS subcontracted that part of the work.

I haven't studied the structure of guns in detail but I think there are 2 main ways they were assembled. Older ones were spot welded while newer ones had their elements fused into glass rods. The former can be dismantled with appropriate skill and care, the latter can't. I hope that the HK assembly can be removed from later guns without the need for extensive dismantling.

As for cleanliness it's just commonsense to keep things decently clean, even if oldtimers' shops were a bit mucky. The only rebuilding shop I've seen was Display Electronics, near Heathrow airport. This was fairly mucky but they turned out good work. They didn't do any work on guns, just fitted new ones as was always the case back then. The 6/6 they rebuilt under my direction in 1986 had its gun rebuilt by (long defunct) Thorn-EMI Electron Tubes. As others have said, there is no dirt problem when pumping and baking the CRT. the muck is outside and the vacuum is inside. However a tiny speck of dirt in a gun assembly will likely cause trouble. Hence if the oven is in the same room as the gun rebuilding then the whole place needs to be kept clean.

We're not talking about microchip fabrication here, no need for clean room facilities, but it's always easier to make a clean place dirty than a dirty place clean:D

As pppenguin says, prewar tubes present many more problems. RACS finally gave up on doing them because of problems with cracks near the anode connector, though tubes have been successfully been rebuild by others.

Our focus is now on two types of tubes: late 40s/early 50s black and white tubes, and early color tubes (15GP22 and 21 inch round). I am concentrating on the black and white tubes, while two other collectors (with their own lathes and ovens) are working on the color tubes.

It is our hope that one day we will tackle prewar tubes.

I don't know if this has been asked but. Will that also include electrostatic tubes like the 7JP4?

I forgot to say that Steve and his team are doing a great job for all of us interested in keeping these old sets alive.

In the (good) old days you could set up a tube regunning shop in an old garage. All the guns were readily available and the skills were quite widespread. Results were a bit variable, the best rebuilders got results that were the equal of the manufacturers, the bad ones went out of business. Now new guns are not available and the skills are not so well known. All makes it much harder.

7JP4s create some additional problems. We would have to have stems made. Shipping of these tubes is an issue since the guns are so delicate. And, I don't know of anyone who has done an electrostatic tube. It is probably possible, and we will investigate it, since there would be a huge demand for that tube.

Here is a progress report on the project:

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

Fired up the oven yesterday. After 1 1/2 hours it was only up to 450 deg F. Another collector has the same oven, but with different insulation. His reaches 775 deg F. in less than an hour. He is using a total of 5000 w for heating, I have 8400. Today I will add another layer of ceramic blanket insulation and try again.

If it were me, slower heating would be better, but using more energy to do it, is not
that impressive..... Sounds like my winter heating bills..... I guess I better check to
see if you swiped my heater.... :)

Is the temp meter working right? Is it digital.... is it set right...?

.

Very daft question. Is your temperature readout set to celsius (as used everywhere except the USA) rather than fahrenheit? 450C is about 840F.

I'm using an analog thermometer that reads 0-1000 deg F.

I've added another inch of insulation on 4 of the 6 surfaces. I'll fire it up today and see how much that helps.

I forgot to say that Steve and his team are doing a great job for all of us interested in keeping these old sets alive...

Here here.
I'd also like to add that I feel this rebuilding project, much like the sets on display at the museum, is a way to keep television history alive. I've heard many people say how ubiquitous picture tube rebuilding operations were in the past and how that's all gone now. Having a picture tube rebuilding operation at the museum is another " functioning exhibit" on display.

The insulation helped a little, but still the max. temperature is 500 deg F.

The problem is leaks, allowing hot air to rush out the top and cold air to rush in the bottom. I will make a gasket for the door and plug all the holes in the inside of the oven.

The insulation helped a little, but still the max. temperature is 500 deg F.

The problem is leaks, allowing hot air to rush out the top and cold air to rush in the bottom. I will make a gasket for the door and plug all the holes in the inside of the oven.

Yep, 50' of stove-gasket and a pail of refractory cement will serve you well in this situation. Also consider throwing a test cadaver jug in while you're still in the test and measurement phase. (Unless I've missed the part where you may have already mentioned including one.) It may have beneficial or detrimental effect on the convection conditions. I'm certain that an unoccupied oven will behave quite differently to an oven with a large hollow glass object inside.


Another way to look at things is you're going to have a sizeable portion of the volume of the oven occupied by a vacuum, so on paper things will heat up faster with less energy input. Obviously in reality the thermal inertia of the glass envelope more than offsets the 35+ liters of vacuum in terms of required heat input.

Are you planning to measure the cool-down time as well? Definitely do this with some sort of test mass of glass. If it is too well insulated you might wind up waiting 6 hours for things to come down to the point where you can safely retrieve them to ambient conditions without catastrophic thermal shock. My experience with glasswork consists mostly of laboratory style jointery in pyrex, and some mucking around with soda-lime pieces. I'm unfamiliar with the whole hot-to-not side of the thermal processing on CRTs and the thermal down-ramp might not be anything critical other than "Don't open door above 160C". Still worth considering in terms of "how long will things take on a per-tube basis" since the oven is a one-at-a-time bottleneck. (Or maybe three if they're 8" tubes and the evacuation system is engineered for it.) In the event that some enthusiast¹ drives a van loaded with all of his dead tubes up from California to be a part of rebuilding them, if each tube requires ~8 hours to oven process he's going to have a LOT of free time to kill given any realistic number of tubes that can concurrently occupy a van.




The literature on the "Champion" plant has all the hallmarks of something you'd find in the text only advertisements at the back of magazines. "Make Money Rebuilding Picture Tubes In Your Garage! Send $5 for our full brochure and catalog to:" type of thing. Sure, we know it works, but its all very rough-and-ready procedures. It does mention "One tube per hour" for the oven, but I think that's a bit generous, even in ideal conditions. I can't find any specific documentation of how long it "should" take. Obviously, "When the vacuum is good enough you can tip-off" is precisely "how long" it takes, but they don't even give estimates for the various size tubes.


On a related note, what are the plans for servicing the pumps prior to the first live-fire testing? High vacuum pumps left idle for long periods, especially if exposed to atmosphere along the way, need servicing before they're ready to suck once more. At the very least the oil will need flushed. That is to say not just a quick drain and fill job. More like drain and fill followed by a run for a few hours, then drain and fill again, pump to hard vacuum, maintain for 90 minutes, and keep the system airtight from that point on. An outright overhaul wouldn't be totally uncalled for, depending on the condition of the pumps.



I hope that no one here is interpreting my posts as doom-and-gloom nay-sayer "born to fail" etc... To the contrary, I very much want this project to succeed beyond all of our wildest dreams. I'm merely trying to ensure that things are considered from all angles so that the project doesn't wind up dying from a self inflicted foot-wound. If I'm pointing out something that might not be wise, I'm going to do my best to provide a proper explanation, and also a workable solution where applicable. I'm not just sitting on the sidelines trying to shoot everything and anything down for kicks.












¹ We're all mad here! :D

There is an established ramp up and ramp down procedure for tubes - different for glass and for metal tubes. Our controller allows up to 64 time/temperature periods. We have documentation from Hawkeye and RACS for this.

I'm not sure having a tube in the oven will make much difference. The oven is about 20 cu ft. A typical 12 inch CRT has a volume of about 1.3 cu ft, while a 21 inch color tube (the largest we will do) is about 5 cu ft.

Our production will be very limited - probably one a day at most.

I agree on your thoughts on volume production, 1 a day is a good idea.

And by all means seal the leaks ! Just think about a house with energy costs...
Seal the lower end, it will be cooler....

You might think about making a "hat" with ear flaps you can just pull down outside
the oven, it may just be easier to deal with.... And you won't give up any inside volume.
Close the door, pull the hat down....

You may find you need to add a heating element too.....

.

It is possible to pump a CRT without baking. This was done for the 6/6 rebuild at Display Electronics in 1986. They gave 2 reasons. One was worries about the state of the pyrex, fears that it might implode due to all the imperfections in the glass. The other was the purely practical point that the CRT was too long for their oven.

The CRT worked very well after rebuild but I don't know how it's doing a few years on. The set with this CRT is currently in store at the National Media Museum, Bradford.

I know that the CRT wasn't left down to air for very long. While the gun was away for rebuilding they fitted the graded seal and rough pumped it. They also fitted a generous amount of getter.

Interesting, Jeff. When we get around to playing with prewar tubes I'll keep that in mind.

As I understand it, the reason you bake a CRT during pumping is to drive out any air and volatiles that might be retained in the glass and gun. I don't know enough about the process to judge what might cause problems with air and volatiles. I also don't know if it's possible to use the RF heater's work coil to heat and outgas the gun assembly without inadvertently firing the getters.

Just curious, would it be possible to get an adequate clean vacuum without bakeing the tube? I know it sound like a strange idea, but is it even remotely possible using modern equipment?

Just curious, would it be possible to get an adequate clean vacuum without bakeing the tube? I know it sound like a strange idea, but is it even remotely possible using modern equipment?

It's a question of process time and the dislodging of adsorbed contaminants, not the modernity of the equipment. A vacuum pump cannot draw contaminants in the tube from a distance, it can only trap them when they travel randomly to the pump.

More progress on the oven, though it still isn't finished. I bought some high temperature caulk (good to 750 deg C.) and sealed all the joints between the steel and frame on the inside of the oven. The caulk hardens like clay.

I was able to get the oven to 700 deg F, which is about what we need. However, when the oven had cooled down a good deal of the caulk had separated from the metal and fallen onto the floor of the oven. This is because of warping of the steel that occurs when it reaches a high temperature. I have the steel attached to the frame with bolts spaced 12-18 inches apart. By putting additional bolts along each edge of the steel I think I can contain the warping and that the caulk will stay in place.

I'm very glad to hear all the progress reports.. It seems like everything is falling into place.. A few years ago many were worried if it will ever happen, and now we are most certain it will..

More progress on the oven, though it still isn't finished. I bought some high temperature caulk (good to 750 deg C.) ..........

I was able to get the oven to 700 deg F, .........

I worry about the mixed units. Didn't a space mission once fail because one part of the team was working in metric units while another was in feet and inches..

I worry about the mixed units. Didn't a space mission once fail because one part of the team was working in metric units while another was in feet and inches..

Quite a few space missions have ended in failure for this type of reason. To my knowledge the Hubble is the only one to have overcome it. Everything else crashed and burned.

However, when the oven had cooled down a good deal of the caulk had separated from the metal and fallen onto the floor of the oven. This is because of warping of the steel that occurs when it reaches a high temperature. I have the steel attached to the frame with bolts spaced 12-18 inches apart. By putting additional bolts along each edge of the steel I think I can contain the warping and that the caulk will stay in place.

Can't you also disassemble the frame-steel interface and put caulk in the actual joint before squishing it together to help seal the joints all the way through?

Quite a few space missions have ended in failure for this type of reason. To my knowledge the Hubble is the only one to have overcome it. Everything else crashed and burned.

Yeah, it's a bit of a problem when you don't notice your problem until it crashes... :sigh:

For Hubble, I'm assuming you're meaning the lens sag issue because they forgot to account for gravity bending the lens while it was sitting on Earth pre-launch?

Yeah, it's a bit of a problem when you don't notice your problem until it crashes... :sigh:

For Hubble, I'm assuming you're meaning the lens sag issue because they forgot to account for gravity bending the lens while it was sitting on Earth pre-launch?

That was not the Hubble problem.

The Hubble problem was idiotic stupid pigheaded project leaders.

There were two different test devices used to measure it.
One, the simpler one, correctly said that it was exactly as it was:
very very wrong. The more complicated, expensive one, was simply
wrong. No one ever checked either test device. No one did a trivial
by-eye test that would have verified which was right, for
two reasons:

1) that doing so required a human to climb a scaffold and that was
deemed both too dangerous and too expensive (building the scaffold,
the by-eye test apparatus was free ... several workers personally owned one, as do I).

2) the idiots said that the by-eye test was not sensitive enough
to detect any possible error. That was, however, assuming that their
already-decided idea that the complicated tester was right was indeed correct: they knew that the by-eye test would be sensitive enough to tell
which tester was correct.

drussell, yes I can put caulk between the steel sheets and the frame. However, the stuff cures like clay and probably wouldn't provide much of a seal.

Maybe you need to forget the calking and go to overlaping strips of sheet steel like
corner molding not tied to the larger sheets so they can all expand and contract
without warping. Maybe tied to the frame, and rasting on the larger sheets inside
the oven, possibly made of several layers covering the area fully, but not a single
piece end to end so expansion will not cause it to warp.

.

drussell, yes I can put caulk between the steel sheets and the frame. However, the stuff cures like clay and probably wouldn't provide much of a seal.

Any members with some TIG skills? Pre-heat the oven and weld the corners up, then let things cool down and see if anything shears off. Since it is just mild steel I don't think it would present much of a challenge even to an "only-occasionally" TIG operator. Stainless would raise the bar a little, but still doable by a non-pro operator.

Your other option is to widen the gaps somehow, and "caulk" them with stove gasket. Caulk here is used in the original nautical term of shoving greased rope in between the decking boards with a mallet and tamping tool, not the modern stuff that comes out of a tube.

Success with the oven. By using lots of bolts to attach the steel to the frame I was able to seal it well enough to get up to 700 deg F in about 2 hours. To improve this, I'll get some stove gasket material and put it between the steel and the frame.

The next issue is the controller. It doesn't work, and I think I may have damaged it by applying 120 vac to the wrong terminals. I might have to buy another one.

I'm going to try this:

http://www.amazon.com/Nomex-High-gasket-smoker-stick/dp/B00CI7A69I

Check out the latest progress report:

www.earlytelevision.org/crt_project.html

Hi,
im just looking to find some info from some people who know what there talking about, I have what I believe to be a 1948 Dumont large screen tv, radio,and phonograph all in one mahogany entertainment center. The TV comes up in middle( very cool ) the unit is large approx. 5ft wide 4ft tall. from what info I do have is this was a high end unit back then.
If anyone can point me in the right direction or any help please contact me 516-707-3686

thank you
Rob
also have other small units ( help ) hate to see history go to waste

thanks again

You have a DuMont RA-101-1A:

http://www.myvintagetv.com/dumont_101a.htm

A better forum to find out stuff about old TVs is:

http://www.videokarma.org/forumdisplay.php?f=19

Steve-

I am happy to read about all the progress that you and others have made with the CRT project. One thought I had, now that I have read both the entire Web page as well as the discussion here: I noted that the heating element is from a convection oven. Would it be feasible to obtain and use the element(s) from a self-cleaning electric oven? During the self-cleaning process, those ovens go up to maybe 800 degrees, if I remember right. Such an element would need 220V wiring.

Steve-

I am happy to read about all the progress that you and others have made with the CRT project. One thought I had, now that I have read both the entire Web page as well as the discussion here: I noted that the heating element is from a convection oven. Would it be feasible to obtain and use the element(s) from a self-cleaning electric oven? During the self-cleaning process, those ovens go up to maybe 800 degrees, if I remember right. Such an element would need 220V wiring.

He is right. We have an electric self cleaning oven. It is 220v and the instructions
do say not to touch or open it, temperatures will reach 750 - 800 degrees....
I have never used the self cleaning option....

.

There is nothing unique about the heating element in self cleaning ovens. The one I'm using with the fan is from such an oven. Mine is 8400 watts at 240v.

The reason I am having more difficulty reaching 700 degrees relates to the size of the oven (4 times the volume of a typical oven) and air leakage.

I am in the process of using an automotive silicon sealer on all the interior joints of the oven. If this doesn't bring it up to the desired temperature I will add an additional heating element - like a stovetop element. I can add about 1400 watts and still power it from my 40 amp breaker.

One thought on 7JP4 rebuilding. There were many essentially identical scope tubes made so if a gun gets shattered in transport or something similar, robbing the parts from a less sought after scope tube may be a solution. It could also potentially be worth wile to rephosphor otherwise identical scope tube types to make new 7JP4s.

Unfortunately, just robbing the gun from a 7JP1 scope tube won't work.

Once the tube is let down to air, the cathode needs to be replaced, because the active oxides become contaminated. If you are going to go through all that trouble, you might as well just rebuild the 7JP4 guns themselves...

There is nothing unique about the heating element in self cleaning ovens. The one I'm using with the fan is from such an oven. Mine is 8400 watts at 240v.
OK, that is good to hear. I hope things go well with the insulation and sealing efforts.

Unfortunately, just robbing the gun from a 7JP1 scope tube won't work.

Once the tube is let down to air, the cathode needs to be replaced, because the active oxides become contaminated. If you are going to go through all that trouble, you might as well just rebuild the 7JP4 guns themselves...

I was NOT trying to say that if the cathode is dead in a 7JP4 to just swap the gun from a 7JP1. I understand that the cathode would need to be rebuilt. Someone earlier insinuated that the guns on 7JP4s were very fragile and may be damaged in shipping despite the rest of the CRT being fine, and I was responding to that by saying that if the gun is damaged beyond rebuild-ability one that could be rebuilt and installed might be obtained from a scope CRT....That and one could potentially make new 7JP4s by rebuilding a 7JP1 and rephosphoring it with P4 phosphor.

I'm hoping someday they can make a bunch of 3KP4s out of all the 3KP1s I've been saving.

.

I'm hoping someday they can make a bunch of 3KP4s out of all the 3KP1s I've been saving.

.

That has the potential of being even more lucrative than doing the same with the 7" CRTs. There would be a lot of happy Pilot TV owners...

Here is a video produced by Bob Galanter that shows the rebuilding process used at Hawkeye:

http://antiquetvguy.com/Web%20Pages/Crt%20Rebuilding/Hawkeye%20Movie%20Page.html

The oven is now working perfectly. Take a look at our latest progress report:

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

The RACS equipment is halfway across the Atlantic. It should be in Norfolk on the 26th, then in Hilliard by about December 1.

Thanks for the update!

The RACS equipment is halfway across the Atlantic. It should be in Norfolk on the 26th, then in Hilliard by about December 1.

It's an early Christmas miracle :).

Excellent news.

Hope they are avoiding the rough seas out here, we're getting tossed around like a bobber in a typhoon! :D

Apparently it IS possible....

But--At all times the cathode is down to air--it MUST be kept above 100 deg C, as its moisture that damages it, not the air itself....
The Heater could be used for this......

I was reading something about Electron Microscope cathodes and the issues they had with them and their longevity/changing/re-using them etc....

Whether its worthwhile/worth the risk, going to the trouble of breaking a tube open to use its gun in a rarer tube by doing this--that would be up to the rebuilder/owner of the tubes....

I don't thhink an oxide cathode (as used in all CRTs we are likely to encounter) will survive being down to air. Pure tungsten and thoriated filaments may well do better but these were superseded in receiving valves in the 1920s. Now only used in some transmitting and high power valves.

The article was very specific....

60/40 Thorium/Barium Oxide Coated Cathodes--as used in the majority of CRT's--and certain Electron-Microscopes.....

The art was to keep them hot therefore attack from moisture eliminated.

Progress report:

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

Very good.

Has the shipment from RACS arrived?

The article was very specific....

60/40 Thorium/Barium Oxide Coated Cathodes--as used in the majority of CRT's--and certain Electron-Microscopes.....

The art was to keep them hot therefore attack from moisture eliminated.

Yeah, most EMs don't use thoriated or chemically treated/oxide filaments - its all pure bare metal. Perhaps some do but the that's not the norm. The mission of an electron microscope typically is to produce a very very fine spot of electrons in the range of nanometers or less at beam currents of up to the range of 100 nanoamps or so. Very different from CRT that need gobs of current to bombard large phosphor screens, trade off is a much larger spot size. So, EMs have very different service compared to the CRT or kinescope used in television.

Filament life in an EM is typically 50 hours or so and the vacuum equipment is designed for easy filament replacement using simple tools. The short life is also a function of cycling EM filaments by exposure to air at lower vaccum (poor vacuum) 10-4 torr to 10-7 torr conditions without the use of getters or baking. LN2 (liquid nitrogen) traps are somtimes used to help remove water vapor. Unlike the EM, a CRT design typically requires complex sophisticated equipment to replace the cathode emitter and gun assemblies need to flashed with getters. Assembly also requires baking to outgas everything inside the envelope - mainly to drive off water vapor and dissolved gases quickly. However, the payoff, if done right, is an extremely high vacuum 10-8 torr or better, with continuous getter activity over the service life of the CRT, which in some cases can be decades - if you get all your sealing surfaces air tight! That's a big 'if' with frit and glass to metal seals.

Most SEM and TEM (scanning and transmission electron microscopes) use solid tungsten wire filaments. The wire is bent sharply to form a tip to form the cathode emitter. For smaller spot sizes and higher brightness (more electron emission) EMs can use LaB6 (Lathanum Hexaboride) emitters. The LaB6 has a unique ability to physically have a sharp tip compared to a tungsten filament that when heated has a fairly low work function for very fine stream of electrons. In this configuration, a single crystal of LaB6 is supported and heated by the tungsten wire. Heat from the tungsten wire causes the LaB6 to emit thermionic electrons.

As an fyi. Pure tungsten and LaB6 cathode filament heaters are often held by posts of MO and RE for support. The tungsten wire is spot welded to the substrate posts, which also acts as conductors for the filament current used to drive up the temperature of the tunsgten. As used in electron microscopes they are typically stored at atmosphere and long term storage. They are not affected by temperature or humidity. It's not required to keep them in a desiccator. Tungsten and LaB 6 will rapidly outgas when gradually heated initially prior to bringing the emitter up to full operating termperature. That process may take several hours.

Here's a link to various emitters used in electron microscopes (SEM and TEM)

https://www.google.com/search?q=lab6+filament&biw=1600&bih=1106&tbm=isch&tbo=u&source=univ&sa=X&ei=hfaJVJrrHsLSoATjyoCwAQ&ved=0CCoQsAQ

Excellent news.. I'm glad everything arrived undamaged..

Hi to All,

RACS shipment to the ETF:

For those who haven't seen Steve's photo on the ETF site, here is the first photo of the container's content which arrived at the ETF on Dec 11th. (Thanks! Steve for the pix and all the hard work to make this happen).

The 2 page listing displayed below list the content.

The numbers refer to pallet numbers and carton numbers, not the quantities of stuff inside. If an exhaustive listing had been required, for instance for gun models, etc. the manifest would have been 20-30 pages long.

Total weight of the shipment was close to 4 metric tons.

Come to the 2015 Convention! you will see everything with your very own eyes.

Best Regards to all and Merry Christmas,

jhalphen
Paris/France

The equipment is at the Museum. Thanks to Jerome for all his help.

We have just started inventorying the stuff, but so far the biggest pleasant surprise is hundreds of cathodes and about a hundred filaments that are perfect for our color and black and white rebuilds.

Cathodes and Filaments ! ! I think Ortho has a spray for that....

.

Very nice to hear that the equipment has arrived safely at the museum.

"Return to USA of RCA non-processed CRTs". This sounds like the answer to the question I first asked last February in this post:

http://www.videokarma.org/showpost.php?p=3096476&postcount=11

Hi Chris,

indeed, this line item describes the 10x 15GP22's sent by Molnar/Galanter/Folsom jr/Kubbe to RACS.

I have asked Steve, as he unpacks the shipment, to make it a priority to check the condition of the returned tubes and inform their owners.

No news yet, but 4 tons is a lot of stuff to unpack.

From memory, 4 tubes were processed, some had up to 5 frit applications + oven passes to try to solve the Anode ring leakage. Also from memory, one tube has a new gun installed, is under vacuum, and from RACS's quote before the shipment left France, the Getter was still silver. The gun was not activated because if the tube leaked, the gun could be retrieved without having to replace again the Cathode and Filament.

Best Regards

jhalphen
Paris/France

We are still unpacking. There are 6 tubes in a crate which we haven't inspected yet. Of the 4 in boxes, one has a broken face and the other 3 look fine.

Hi Steve,

Thanks! for the update.

The 6 tubes in a crate are most certainly Mike Molnar's. He had a special wooden crate built with a snug compartment for each 15GP22.

From memory, as i saw it at RACS, it was painted black and may have castor wheels.

The 4 other CRTs are 2x Folsom jr/Galanter and 2x Kubbe.

By "broken face" do you mean that the CRT faceplate bowl has separated from the Anode ring? - is the phosphor plate broken?

Best Regards

jhalphen
Paris/France

I notice that there are people who collect classic coin op arcade games... I wonder if you'll get alot of those guys wanting the CRTs rebuilt.. They made alot of vertical type of CRTs especially in the early 80s types of games, that are hard to find to replace... That will be interesting if you all would be able to rebuild these CRTs too..