Filament in tubes sag when they are heated. If you operate a tube on it's side the filament can sag enough to short to another element. When a certain plane is mentioned a tube filament won't sag enough to short when mounted in this direction. Still best to mount tubes vertically.
Norm
:It's to do with the heat of tube. Heat goes up, needs to be kept as cool as it can.
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 Sir Chris . . . [ In the interim of getting my image. . .I see that Sir Norm has covered it . . .but I'm adding my initial info also. . .my first image came back as someone elses' high rise skyscraper with scads of reflective windows ! ] That covers the filament routing , the next consideration, its shape, being a band of tungsten instead of a round wire, thus affording more active surface area exposure along with accepting more thorium coating .
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: :Thankyou Warren ,Norm and Edd for your info!!I accidentally hit "SUBMIT FOLLOW UP" three times.Whoops! : :Sir Chris . . . : : : : :[ In the interim of getting my image. . .I see that Sir Norm has covered it . . .but I'm adding my initial info also. . .my first image came back as someone elses' high rise skyscraper with scads of reflective windows ! ] : : : :WOW Chris you must have been REAL curious, to have posted thrice . . . .or else had an onset of the hiccups ? : :Plus what is the proper protocol . . .need I now, reply to each ? : : : I also see that you also answered your own question, I will , hopefully, clarify the situation a bit. : :Now I currently don't have an 80 . . . .or I initially was thinking of a 5Y3 or 5U4. . .in hand to mechanically compare for referencing. : : :I do remember the arrangement of some manufacturers using a rectangular stringing of the tungsten heater strip up from the base wire terminal where it was crimped or later on , welded or spot welded and then the routing goes up parallel to the enclosing plates infrastructure and then passes thru the top mica support washer. It then makes a bend and travels over a bit to another symmetrically placed hole in the same washer and makes its like travel downward to the companion support wire on its other side. Repeat the procedure for the companion plate ,way over on the other half of the tube. : : :That covers the filament routing , the next consideration, its shape, being a band of tungsten instead of a round wire, thus affording more active surface area exposure along with accepting more thorium coating . :(BUT, also exposing more gravitation mass when mounted in one plane!) :The next effect would be the sag condition of that heater stringing. If the tube was mounted vertically , there would be no problem, but if you made a variant , in mounting it a hoz position, here is what could happen. : :Refer to this rough rendering of the top view of one section with the black peripheral portion representing the plate cylinder and the red portions being a top view of the hot filament. : :Now if you had mounted the tube in the desired horizontal positioning . . . as is shown in the first illustration, the width of the filament band would have minimal possibility of filament sag from gravity. : :HOWEVER, should you have positioned the tube in the second position of mounting, the wide area of the filament band is more subject to gravitational sag and its transitioning down towards the plate portion below it. : When the filament is cold it is quite taunt, but with heating it will be subject to sagging down and getting closer to ever diminishing that safety margin of insulative spacing between the lower filament position and the plate proper below. {Arrow } (The filament half at the top is of no consequense , since it is not sagging down towards a plate portion, but merely towards the other half of its filamemt proper.) : : :A time related conditioning by gravity and repeated heat cold cycles will result in a gradual onsetting of an arc on the bottom filament half. . .until that drastic day when the decreased interelectrode spacing results in a flashover and then an arc light effect between the plate and filament. That is the time when you can see the importance of also including secondary fusing.. . . versus raw AC on the filter condensers for meltdown and the loss of the transformer. :PLUS , you certainly would then know about that fine print messaging about the mounting positions of the tube , should hoz placment in its mounting have been required. : : : :Illustration: . . . . (its not a HOT AC receptacle. . .hi. . .hi) : : : : :  : : : : : : :73's de Edd : : : : : |
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