29-08-2014, 08:29 AM
Yes Al, that would be an interesting experiment.
So far as I can make out a relatively large grid current results in a dramatic drop in the grids input impedance WRT the cathode due to the diode action of the grid and cathode.
I'm thinking the large xtal current is due to a combination of the above and the internal valve capacitances including any effective capacitive increase due to any Miller effect.
Here's a thought, if the Miller effect was indeed large how would a xtal osc circuit designer specify the load capacitance as regards to ordering a xtal specified for parallel mode operation, so far as I can make out load capacitance is typically only around 20 to 30 pf according to various xtal manufactures web sites.
Lawrence.
So far as I can make out a relatively large grid current results in a dramatic drop in the grids input impedance WRT the cathode due to the diode action of the grid and cathode.
I'm thinking the large xtal current is due to a combination of the above and the internal valve capacitances including any effective capacitive increase due to any Miller effect.
Here's a thought, if the Miller effect was indeed large how would a xtal osc circuit designer specify the load capacitance as regards to ordering a xtal specified for parallel mode operation, so far as I can make out load capacitance is typically only around 20 to 30 pf according to various xtal manufactures web sites.
Lawrence.
