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Old 8th May 2014, 10:38 AM   #1
Keit is offline Keit  Australia
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Default Design data on dry battery tubes

Does anyone know where I can get internal design parameters for battery tubes such as 3V4, 3A5, 1S5? I am particularly after things like diameter of filament (without oxide coating), thickness of oxide coating, area of emitting surface, filament temperature.

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Old 8th May 2014, 11:49 AM   #2
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That sort of information is usually a trade secret, and will vary from one manufacturer to another and from one valve version to another. The people who knew are probably dead by now. Some information of that type may appear in advertising or in research papers, where the maker was boasting about his superior technology.
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Old 8th May 2014, 01:37 PM   #3
Keit is offline Keit  Australia
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I'm hoping there's someboy around who knows. Quite a bit of internal RCA documentation that gives this information for common mainstream AC receiving tubes like the 6SK7 has popped up on the internet.
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Old 9th May 2014, 01:16 AM   #4
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According to Deketh "Fundamentals of Radio-Valve Technique", the battery fed tubes where primarily designed to conserve battery life and minimize # of batteries. So low current filaments, and low gm design. The pentode screen grid was designed to work at the same voltage as the B+. RCA's tomes "Vacuum Tube Design" and "Electron Tube Design" and RCA "Electron Tubes, Vol I and II" should have info on these. Pete Millett's site has these:

Technical books online Tube theory & circuit design

Ironically, late in the tube era, after battery tubes had long gone by, "dark emitter" cathode coatings were developed. These took less filament power and glow dimly, some late TV sweep tubes use them.

And in the year 2000, room temperature cathode coatings, using nickel/titanium thin films were developed, which don't need a filament at all. These are used in satellite microwave tubes now.

interesting thought
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Old 11th May 2014, 11:36 AM   #5
Keit is offline Keit  Australia
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I was already aware of excellent Pete Millet's site. None of the books there have what I need. Some have the information for transmitting tubes and wet battery directly heated tubes, but not for the dry battery tubes I'm interested in.

The local university's libray has a copy of Deketh's book. That does give the infor I want for what it calls "modern" dry battery tubes - no type numbers given. But since it was published in 1949, it probably does not apply to the American miniature tubes I'm interested in. Even though RCA and others started selling these tubes in 1940, I don't think Philips sold them until about 1949, under cross-licencing agreements they had with Amarican affiliates.

Deketh states that "modern" battery tubes have tungsten filaments. The way the filament current varies with voltage in miniature tubes such as the 3V4 indicates the filament cannot be pure tungsten (it could be an alloy), though a version (3V4WA) with greater shock and vibration tolerance was available for military applications. This was achieved by employing a pure tungsten filament according to Tung-Sol literature.

I recall that in the early 1960's and American company developed a cathode that only needed heat upon switch on. Once the emission was established the heaters could be turned off. They are described in a contempary issue of the Australian magazine Radio, Televison, and Hobbies if I remember right. With transistors well established by then, one wonders why they bothered. It was known since the 1920's that secondary emission could be used to create a controllable electron stream without joule heating the cathode, but it required a negative HT supply as well as the +ve HT supply for the grid controlled electron stream. Cheaper just to heat the cathode.
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Old 12th May 2014, 12:25 AM   #6
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There are some books on general tube design like "Vacuum Tubes" by Spangenberg, "Thermionic Valves" by A.H.W. Beck and "Theory and Application of Electron Tubes" by Reich. Then there are some techniques books like "Handbook of Materials and Techniques for Vacuum Devices" by Walter H. Kohl and "Handbook of Electron Tube and Vacuum techniques" by Fred Rosebury.

"Electronic Designers' Handbook" by Landee, Davis, Albrecht has a few pages on cathodes. From perusing that, it looks like barium and strontium oxides directly on a nickel/alloy filament would be preferred for battery type tubes, for emission efficiency at low B+ voltages.

----------------
Any info on how those heat once only cathodes worked?
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Last edited by smoking-amp; 12th May 2014 at 12:29 AM.
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Old 12th May 2014, 03:54 AM   #7
Keit is offline Keit  Australia
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Thanks. I've already checked out Sprangenberg etc - they are on Pete Millett's site.

The filaments in the 3V4 cannot possibly be nickel or a nickel alloy. The RCA books on Pete Millett's site state that nickel was used in filaments but they were talking about transmitting tubes and older wet battery tubes. Quite apart from the fact that the filament temperature would be too low with nickel, nickel being ferromagnetic, there would be a very noticeable kink in the filament voltage-current curve as the filament temperature passes through the Curie point. I've carefully measured the voltage-current curve of several known good tubes to 4 digit accuracy, and there's just no sign of a kink.

The best fit of calculated performance to measured performance I can get so far is by basing calculations on a pure tantalum filament 23 micrometer diameter with an 8 micrometer emissive coating. (Deketh says "modern" tubes have a 10 micrometer coating). However tantalum is extremely expensive, so I'm not trusting my calculations. It's more likely some refractory metal alloy was used.

I can't remember how those "heat only on switch-on" tubes worked. I'll have to dig out the relavent R,TV&H article.

Keit

Last edited by Keit; 12th May 2014 at 04:09 AM.
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