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  #31  
Old 10-04-2014, 01:18 PM
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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.......
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  #32  
Old 10-05-2014, 03:48 PM
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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
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  #33  
Old 10-06-2014, 03:13 PM
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Since the galvanized was not used, what metal is now being used?
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  #34  
Old 10-07-2014, 06:16 AM
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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.
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  #35  
Old 10-07-2014, 08:25 AM
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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-Oleu...specifications
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  #36  
Old 10-07-2014, 09:46 AM
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The glass is -3dB.
 
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Quote:
Originally Posted by Steve McVoy View Post
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-Oleu...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."
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  #37  
Old 10-07-2014, 12:17 PM
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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...

.
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Last edited by Username1; 10-07-2014 at 12:29 PM.
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  #38  
Old 10-07-2014, 01:02 PM
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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,
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  #39  
Old 10-07-2014, 01:25 PM
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The glass is -3dB.
 
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Quote:
Originally Posted by Username1 View Post
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.
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  #40  
Old 10-07-2014, 01:25 PM
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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.
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  #41  
Old 10-07-2014, 04:07 PM
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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.
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  #42  
Old 10-08-2014, 03:12 AM
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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
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  #43  
Old 10-08-2014, 05:58 AM
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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.
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  #44  
Old 10-08-2014, 08:19 AM
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I don't know if this has been asked but. Will that also include electrostatic tubes like the 7JP4?
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  #45  
Old 10-09-2014, 02:08 AM
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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.
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