Posted by Steve [ 204.42.22.35 ] on April 14, 2005 at 13:33:49:
In Reply to: AC filaments posted by Tnuctipun on April 14, 2005 at 08:25:51:
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
[ Tubes Forum ] [ Help ]