[ARC5] Filament Question

[Tim Des]

*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