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Old 25th July 2014, 04:43 PM   #1
Keit is offline Keit  Australia
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Default Filament tension spring material

Any folk who used to work in a tube factory in this forum? Or folk with a really comprensive book on tube engineering?

At the top of directly heated tubes is a spring, which tensions the filament, so that it stays straight and centrally located while expanding as it heats up. In battery tubes such as 1T4, 3V4, and the like, it is a simple bent wire cantilevered out from a side mount point. In rectifiers, it generally doesn't look quite like a spring, but it is a spring.

I would like to know what, battery tubes, this spring was made from.

It also serves as a thermal isolator, so not too much heat is lost by conduction out through the connection lead structure. (If you look carefully, there is a thermal isolator at the bottom end of the filament as well. But it is not a spring, and according to an RCA book on Pete Millet's website, it's Invar - an alloy with a high thermal resistance.) The filament end of the spring may run as much as 500 C, so it must be a metal or alloy that retains "springiness" in the face of thousands of heating and cooling cycles.

I have been working on a computer program to accurately calculate tube performance in all respects, so I can determine objectively, by non-destructive testing, what's different about equivalent tubes made in Russia and China, often reported to not sound as good. The computer program has thown up some anomalies. Analysing mathematically shows that the filament tension spring contributes significantly to the filament electrical resistance.

Last edited by Keit; 25th July 2014 at 04:52 PM.
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Old 25th July 2014, 09:41 PM   #2
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Hi,

No idea about battery valves and how differently they were made but AFAIK the materials used we're usually tungsten, thoriated tungsten and rhenium tungsten. Sometimes coated with an aluminum oxide.

One guy who may know more about this is Francis Ibre, author of various books on electron tubes. You may be able to get in touch with him through elector.fr's forum.

Interesting reading material:

http://http://mysite.du.edu/~etuttle...ct27.htm#Batts




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Last edited by fdegrove; 25th July 2014 at 10:08 PM.
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Old 25th July 2014, 09:46 PM   #3
Jsixis is offline Jsixis  United States
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from reading tube manuals I would think everything is tungsten like the poster above me said. The temperatures in tubes were 600 degrees for the heater wires and in the kelvin range for the actual conductance.
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Old 26th July 2014, 09:09 PM   #4
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Springs in battery tubes where made of nickel. even the filaments of some common tubes 5y3gt where nickel.

Springs in transmitter tubes are tungsten. they need to be operating temperatures of those fillaments are around 2300C

Anodes are mostly made from aluminium clad iron since nickel is quite expensive.
Feed through wires, are dumet, the other end are made from
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Old 27th July 2014, 12:48 AM   #5
Keit is offline Keit  Australia
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Thanks, v4lve lover. Do you have a reference, source, or reason to believe the springs were nickel?

I know that the anodes in battery tubes were nickel. They were not any sort of clad iron, although I do have a couple of battery tubes in my collection (made by AWV) that have blackened anodes. I assume they were made during World War 2 and AWV may have had to cope with a shortage of bright nickel. I've pulled some expired battery tubes apart and tested the anodes chemically. Unfortunately the springs are far far too small to test in my home lab.

Incidentally, by plotting a graph of filament current against voltage, it is easily shown that the actual filaments in most miniature battery tubes like 1T4, 1S4, 3V4, 3A5 etc were tungsten/molybdenum 50:50 alloy (ie Dowmo alloy). Nickel would give a different shape curve.

Last edited by Keit; 27th July 2014 at 12:55 AM.
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Old 27th July 2014, 11:29 AM   #6
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I have some battery tubes in front of me, their mostly the Philips 90's series E.G DF94 and the tension sping is very bright, so its unlikely that it is made of tungsten. Furthermore the low operating temperature of battery tube fillament does not warrant the use of tungsten in filament springs.

The blackening you describe is to increase power handling, and its a deliberate process where carbon residue is placed on the base material. This residue was mostly from burning benzene starved of oxygen.

The anodes on battery tubes are indeed mostly nickel, I was somewhat mistaken. Low power tubes use nickel as it requires less out gassing which greatly speeds production.

The use of aluminium clad iron was common in postwar tubes, as I've read somewhere that the Germans developed this to overcome shortages of nickel.
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Old 27th July 2014, 12:40 PM   #7
Keit is offline Keit  Australia
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Thanks again v4lve lover. Makes sense. I visually inpected the tubes I have, but the spring is too tiny for me to decide on its' brigtness, even with a magnifying glass. But my eyesight is not that good - I have a genetic defect that means I do not have properly formed foveas - the central part of the retina that is supposed to resolve fine detail.

I was aware that the blackening on anodes is to improve power handling, but that is unwarranted on battery tubes - especially as the black anode tubes I have are 1H5GT's - a 1st audio stage triode-diode. Even in the 3V4 (= DL94 I think) output valve at maximum ratings, the anode temperature by calculation is only 385 K. That's why I supect that my 1H5's were made with blackened anodes due to some factory shortage or operational problem. Even the detector diode plate is blackened - that only gets to dissipate picowatts!
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Old 27th July 2014, 12:50 PM   #8
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Well some plate material was supplied already carbonized, as opposed to coated in carbon residue and then glowed. you can keep these apart by the fact that pre coated anodes are quite shiny and even, whilst carbonized ones have a grainy structure.

It could very well be that this material was used on every tube regardless of power dissipation requirements.

This might interest you: TV Manufacturing: "The Reasons Why" 1959 RCA Desiging and Making Televisions - YouTube from minute 9 onwards this promo describes tube manufacture.
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Old 27th July 2014, 04:52 PM   #9
Keit is offline Keit  Australia
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I enjoyed the film, though it says nothing useful about tube design/engineering. It reminded me of a time long gone in the electronics industry and elswhere:-
# The engineers wore suits, white shirts, and conservative ties. There was always a few that wore bow ties. They were adressed as "Sir", or "Mr Xxxxx" and treated with respect.
# For some reason I never really worked out, virtually no engineers were female, but female chemists and physicists working in the labs were common.
# How to design in quality was not perfected then, so a lot of testing was done at every step and below spec parts caused batch rejection.
Beginning in the 1980's:-
# Enginneers dress casually and get addressed as in "Hey, Fred...."
# There aren't the female chemists and physicists in the labs now, because the labs have gone.
# Industry has learnt to focus on checking that the process is a quality (ie uniform) process, and if it is, you don't have to do all that parts testing.
One thing that amused me: The film shows a girl using side cutters to trim excess component wires AFTER a printed circuit was dip soldered. Industry learnt early on that that led to too many intermittent faults. Quality in printed circuit making is crimping or bending the leads so the parts won't fall out, triming the leads with a high-speed cutter, and THEN dip soldering.
Using a massive granite table accurate to 0.001 inch and vernier height gauges as depicted in the film to check the location of punched holes in a TV chassis seems a considerable overkill. In a factory I worked in, they used a metal mask and a lamp, set up in such a way that light was blocked by either the chassis or the mask - the whole thing checked in one step automatically.

Last edited by Keit; 27th July 2014 at 04:56 PM.
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Old 27th July 2014, 07:17 PM   #10
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Heh, from what I've heard and read, the engineering jobs overseas have been transformed in some sort of dillbertian hell. But then again competition is stiff, in the American race to the bottom.

Oh well, you aren't the only one nostalgic for the engineering culture from the 70s and 80s.

(OT)
In Holland, Philips, once had 250,000 people employed which dropped quickly in the early 90s

That led to a huge amount of electrical engineers in search of a job, which ruined the job prospects for anyone wanting to work in the industry in the 90s

25ish years later most of this surplus has vanished and there has been a huge surge in demand for electrical engineers, when I visited Uni they told me for every 100 graduates there where 300 Jobs, however I should ideally really get that in writing

I'm told by my father, who has a B.Sc degree in chemistry that the story in this field is similar. He has worked in insurance for the last 20 ish years

Last edited by v4lve lover; 27th July 2014 at 07:22 PM.
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