| Re: AC filaments [message #8893 is a reply to message #8892] |
Thu, 14 April 2005 12:33   |
Steve
Messages: 83
Registered: May 2009
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Viscount |
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Good question Doug. Actually, virtually none. Grid current can start to flow when the grid is 0, or even a tenth or possibly a few tenths negative with respect to the cathode/filament. Alot depends on the tube condition.
And only a very smallest part of the cathode/fil needs to be in this condition. Thus most of the cathode can be positive with respect to the grid and if a sliver of the cathode is near zero vs the grid, current will start to flow.
The input Z will start to fall relatively rapidly. Of course, having an AC current will mean that the fil/cathode could be negative with respect to the grid during only a portion of the 60hz cycle. So the input Z could swing from near infinite to low during each 60hz cycle.Take care and hope this helps Doug. Steve
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