[ARC5] Filament Question

[Bill Cromwell]

Hi,

The tubes in *this* thread use flashlight batteries for the filaments 
and a AA can run one or two for quite a long time. This is not your 
Eimac ceramic tube and not even a 6146 or a 6SN7.

73,

Bill  KU8H



On 10/03/2015 12:46 PM, Tim Des wrote:
> *On Sat, Oct 3, 2015, at 12:27, Robert  Eleazer wrote:*
>
> *> Would it be better for the longevity of those tubes to rewire the >
> filaments so that they are ON at all times …*
>
> *Getting the Most Out of Vacuum Tubes* by Robert Tomer 1960
>
> http://www.tubebooks.org/Books/Atwood/Tomer%201960%20Getting%20the%20Most%20Out%20of%20Vacuum%20Tubes.pdf
>
> *Technical Books Online* – Many other books on tubes
> *http://www.tubebooks.org/technical_books_online.htm
> <http://www.tubebooks.org/technical_books_online.htm>*
>
> *The 6146 Family of Tubes by *Glen E. Zook, K9STH
>
> http://www.n6wk.com/kenwood/The_6146_Family_of_Tubes-1.doc
>
> *Reliability Factors for Ground Electronic Equipment*, *Keith Henny, 1956
>       *(See the tube section in Chapter 8)
>
> http://www.tubebooks.org/Books/Atwood/Henney%201956%20Reliabilty%20Factors%20in%20Ground%20Electronic%20Equipment.pdf
>
>
>
> Tomer’s book is heavy on generalities and light on details. No references
> or specific studies are sited. But, in keeping with other Howard Sams’
> books, it is very readable.  I do not know if he is expressing a singular
> or consensus opinion.
>
> For example, on page 11 Tomer states, “… having been cycled on and off many
> thousands of times. …a stretching of the tungsten heater wire which leads
> to eventual fracturing.” Whereas on 8-18, Henny states “Generally, it
> appears that well-designed heaters will suffer little from increased
> burnout rates as a result of cycling.” So, as many answers begin, "It
> depends..." on when the tube was made, I guess.
>
> They do, however, both agree that the leading cause of heater failure is a
> filament voltage measured at the tube exceeding 10% of that recommended.
> So, in theory, a transformer designed to output 6.3 V at 110V input, would
> put out 7.2V (14%) at 126 V input. Concern about filament voltage ratings
> (and vibration) may have led to RCA’s introduction of the 6146A. See Zook.
>
> Henny’s book cites references and has well labelled graphs. Also, page 8-18
> contains practical temperature-reduction techniques. Excess temperature
> seems to be the root of all evil in electronics.
>
> Tim Desiato   WA8LHB
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