[Amps] Dimished Tube Life

[Paul Decker]

Hi Group, 



I've watched a few of these questions go by over the years, and it made me wonder. 



When is a tube considered at it's end of life?   Of course a tube like I posted about last week, where there is a grid - cathode short, is (at least right now) at its end of life.   But if over time the tube is simply having reduced output or "going soft", at what point is it considered "no good"; at 95%, 80% 75% output?     



 I'm sure there is a technical answer, but there is also a real world answer, as an example, I would be perfectly happy if someone sent me a "soft" 3-500z  ;)    It would not bother me in the least if it was only capable of producing 75% output, I'd probably be perfectly happy with  tube that produced 50% output as it's better than the 0 I have now.  



I was an RM on subs, we ran our urt-23/am3924 PA's which use a pair of 4cx1500B's 24/7 for over 80 days at a time.   The only time we them down was to do any preventative maintenance and when we transferred our guard to the shore com stations.    On the other hand, we rarely ever transmitted, so they just sat in standby.  In fact, on the boat I was on, there were probably more hours logged transmitting on the amateur bands than on the military nets.   If any of you have a contact from me between 1986 and 1992, likely it was from the boat.  



73, 
Paul (KG7HF)