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In Reply to: RE: ? How to Calc optimum grid Leak R? posted by kellymon on November 02, 2009 at 12:13:30
it's really called "grid grounding resistor." a grid leak resistor is the kind that makes use of grid leak to bias the tube so no cathode resistor is needed. those are in the vicinity of 10-50 megohms.
a small leak and a small grid-resistance-to-ground resistor makes the grid set to ground, essentially. hence a grid grounding resistor.
a large leak and a large grid-resistance-to-ground resistor makes the grid more negative than ground, setting up a Vgk bias with respect to grounded cathode. the negative potential that floats there is caused by electrons hitting the grid and not drained away by a little leak, and so voltage starts to settle to a steady DC point until leakage current out grid equals Vg/Rg, and there makes the steady DC bias condition.
to "see" the current flow one must remember that electron flow direction is the opposite of standard positive current flow. So electrons hit grid and leak down grid-to-ground. But the positive direction current flow diagram for a grid leak biased triode is Ip from plate to cathode meeting up with Ig from grid to cathode = total cathode out current to ground.
just had to nit pick.
-kurt
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