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In Reply to: Re: You know, that actually makes some sense... posted by Jeff A W on April 4, 2007 at 11:47:13:
Regarding the glass, I'm no expert on this, but clearly there were lots of variations and factors. There's a whole chapter on glass as used for tubes in the 1962 RCA Electron Tube Design volume. Most receiving tubes used relatively softer glasses, defined as working temperatures during manufacture <1000 deg C. Important aspects include sufficient thermal expansion coefficient to work with the chosen lead out wires (rather than expand differentially and leak when the tube gets hot), also electrical resistivity. We think of glass as an insulator, but some are more so than others. When electrical conduction occurs in glass, as it can between lead outs/pins connected to plates and other elements, for example, it changes the actual structure of the glass, reducing the mechanical integrity. Such electrolysis is also highly temperature dependent. I believe electrolyisis and the migration of sodium ions in particular in interaction with lead compounds in the glass is one reason the bases of glass miniatures can gradually turn dark grey with extensive use, like some people look out for in e-bay "NOS" 12AX7s.Bendix touted that the glass envelopes of some of their missle-proof Red Bank tubes were routinely tested by surviving 3 mins in boiling water immediately followed by three minutes dunking in ice water!
Follow Ups:
Interesting... That reminded me of a book in my stash I picked up a while back and never looked at, until now... It is Materials and Techniques for Electron Tubes By Walter H. Kohl. (1960 Reinhold Publishing co.) Kohl was Senior Engineering Specialist, Special Tube Operations Sylvania Electric Products, inc. (A subsidiary of GTE) This book is a Gold Mine, if you are interested in the materials used in the making of tubes. There is a whole chapter (70 plus pages) on glass itself, and another chapter on joining glass to metals. A chapter on mica and individual chapters on all the different metals used. And enough charts and graphs and equations to make you dizzy.
A quick glance told me that yes, much of the glass used in tubes came from Corning, (In Corning NY of course, between Bath and Elmira) and there were some 150 different formulations of PYREX. The other big glass supplier was Kimble made by Owens Illinois.
I'm going to need to go back to school to understand this book...
--Matt
"You know why is that?"
Great reference for this stuff, Matt. Kohl also did an earlier book that I've seen, but I think yours is the definitive one. I believe these are available in the "obsolete" stacks at the uptown Tulane University library in New Orleans, at least they used to be . . .The huge RCA book also discusses PYREX in particular, I'll have to take a look.
Jeff-
Yep, this book states that it is a completely revised version of the 1951 book "Materials and Technology for Electron Tubes" It doesn't say if Kohl wrote the earlier version, or what other books he wrote, but...
It also says the earlier version had FOUR chapters on glass, which were condensed down to one for this version. It also says that Kohl was giving a Graduate course on "Tube Techniques" at Stamford and that this book, as well as the earlier version were seen as advanced texts for Tube Technicians.
You would have to wonder if they realized in 1960 when the revised book came out, that not even 10 years later tubes would be virtually gone from consumer electronics. (Except for TV's of course. And computer monitors) And that so much tube manufacture would quickly end in the US.
--Matt
"You know why is that?"
Matt- I was looking some more at the 943-page RCA "Electron Tube Design", which was also derived in part from lectures for RCA engineers and "privately issued by Electron Tube Division, Radio Corporation of America, for use by its employees and for restricted distribution".There are two chapters on glass, "Glass For Receiving Tubes" by J. Gallup, and "Glass and Its Properties and Seals" by J.C. Turnbull and G.E. Eiwen. As it happens, these are exactly 40 pages altogether. The first is something of an intro and describes properties, the second gets much more into the nitty gritty, as it were. By my count, 54 types of glass are explicated, at least 18 of which are identified as originating in Corning, e.g., Corning 8160, 8161, 0083, 9010, 9019 3320, 7761, etc. etc.
One thing that becomes apparent is that in some tubes more than one type of glass was used, for stem vs. bulb, etc.
Switching overseas, Philips published the "Philips Technical Review" out of Eindhoven in the 1940s and '50s, and I remembered an article I'd copied on "The Life and Reliability of Valves" (in vol 18, no. 7, 1956-57) had some discussion of glass issues in relation to the manufacture of their "SQ" tube series. They noted that glass even of a specified type was "not a perfectly constant product", and required test runs for adjustment for each production run. Variables in the automatic sealing machines also had to be fine tuned continuously. It appears that Philips also championed the immersion of sample tubes into boiling water followed directly by plunge into cold water testing, on an hourly basis during valve production.
I was hoping someone would kick in with more on Westinghouse tube production during the '50s-'60s too.
I was just made aware of this website today...
Technical books scanned and put online in PDF format...
--Matt
"You know why is that?"
Yes, but thanks for making sure. Maybe he'll do some Kohl next!
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