Tube life

microstrip

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May 30, 2010
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I have owned tube amplifiers since decades and expected tube life was a subject that always interested me, particularly as most NOS tubes are only available in non certifiable condition.

Although this subject is very seldom referred it was studied in the 40's and 50's, particularly for post-office repeaters in the UK after WW2 - tubes were scarce, and should be used only for replacement of tubes that were expected to die soon, preventive systematic replacement could not be considered, and for tube computers, that used thousands of tubes.

I have found several references to techniques that relied of testing the tube on reduced filament voltage, but could not find accurate descriptions of the method. The best I have is this summary from a Soviet Audio article from 1958, classed by the NASA in 1962. Considering how easily we can now measure noise spectra - I do it to select tubes for my ARC REF40 preamplfier I am considering trying it. The summary can be downloaded from NASA servers: https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20160003541.pdf

Do you have any articles or information on this subject?
 

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