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| Re: What is the mechanical condition of the Low V? (664827) | |||
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Re: What is the mechanical condition of the Low V? |
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Posted by SelkirkTMO on Sun Aug 10 22:32:39 2008, in response to Re: What is the mechanical condition of the Low V?, posted by JournalSquare-K-Car on Sun Aug 10 21:03:58 2008. Expansion and contraction of the filament over many cycles will cause the coatings to wear off and eventually you end up with a heater/cathods short. Sometimes, doesn't matter if both the cathode and one side of the filament are at ground, but most of the time you'll get hum or humbars in video or worse, the short will cause the filament to go "pop" ... all depends on the cathode resistance and how the filament is wired up.Vacuum tubes generally don't do high frequencies well, have rather non-linear conductance curves, have wide variances in the same type tube owing to small differences in internal dimensions, and of course die. And from the first time you light one up, the emission from the cathode material goes down hill from there until they eventually don't conduct any more at all. There's good points to all technology and tubes are useful for some things (for example, an electromagnetic pulse is far less likely to trash a tube circuit than solid state) but really awful for others. And like semiconductors, tubes will normally pass DC in one direction only ... but the minute you light up a tube circuit, from that moment on, it's only a matter of time before it dies or fades away. :) |
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