[ARC5] Filament Question

[Glen Zook]

For indirectly heated tubes, leaving the heaters ("filaments") on will definitely increase the longevity of the tubes.  Of course, one has to consider the cost of the electricity to keep them lit!
An example of leaving the heaters "on" and the longevity of them happened a few years back.  In the very early 1950s, a Motorola base station was installed in the attic of a building.  Over the years, the base station was abandoned, the antenna was removed from the roof of the building, and, basically forgotten.  However, no one unplugged the unit and it continued to operate for over 60-years.
When the unit was discovered, someone decided to see if it still worked.  Although the unit was no longer type accepted ("certificated" is the new "buzz word" for type accepted), and could not legally be used today, the transmitter was still putting out full power and the receiver sensitivity still met the original specifications after being "on", constantly, for over 60-years! Glen, K9STH Website: http://k9sth.net
      From: Tim Des <timpdes at gmail.com>
 To: arc5 at mailman.qth.net 
 Sent: Saturday, October 3, 2015 11:46 AM
 Subject: Re: [ARC5] Filament Question
   
*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.