Posted by Russ [ 209.214.16.60 ] on December 31, 2005 at 10:02:07:
In Reply to: Re: Small HV caps, and pentodes driving power triodes posted by PakProtector on December 31, 2005 at 09:00:56:
I dropped Damir an email about a post over yonder from J.Rankin in regards to questions I had about grid chokes. He is a very knowledgable guy and had some great info. I encourage you to look for the post. He states, "the self capacitance of the choke is multiplied by the Miller Effect and this also degrades the higher frequencies". Not sure I see why this should be but if we take it as fact it is something to consider. He also states a mu follower should not be used with an inductive load and perhaps even that a CCS loaded stage would be a poor choice.
When you drop an inductor on the grid things get complicated in a hurry. For example many will point to a lower DCR path if and when grid current is drawn. True for grid current caused by gas molucules but false for grid current from driving the grid positive. Moral being a resistor across the choke is likely to be required.
Thorsten has good info using coax in the way you mention and has always been willing to answer questions.
Why all the interest in pentode/cascode stage? Just to get a lot of gain? I think I'd want a buffer between a pentode/cascode and a reactive load. Never cared for cathode followers...maybe an anode follower (if not a PP stage)....you can pick the feedback ratio to strike a balance between gain and output impedance. Likely you guys have thought all this thru but I have not followed y'all so forgive me if i suggest things that you have already worked out.
Russ
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