Estimate Miller of Triode Strapped Pentode

dsavitsk · 12th January 2009, 11:23 PM

Is there a good method to estimate the Miller capacitance of a triode strapped pentode?

ray_moth · 13th January 2009, 01:43 AM

It makes sense for it to be Cg1g2 X stage gain. I'm guessing that the plate is too far from g1 for there to be a significant capacitance between them, but I could be wrong.

Poindexter · 13th January 2009, 02:29 AM

That sounds right to me; after all, that's the idea of a tetrode in de foist place, no?  The problem would be to find this capacitance.  The datasheets very seldom give such data for trioded pentodes; we're lucky to get plate curves.

I wonder, would this spec have to be tested for on a hot tube in-circuit, or could we just stick an LCR meter on the appropriate pins on a cold tube sitting on the bench?

Aloha,

Poinz
AudioTropic

ray_moth · 13th January 2009, 05:27 AM

Hi Ponz,

I don't see why the tube has to be hot to get this measurement. Temperature would make a difference, I suppose, but it should be slight.

12th January 2009, 11:23 PM	#1
dsavitsk Crusher diyAudio Member Join Date: Jan 2005 Location: Chicago	Estimate Miller of Triode Strapped Pentode Is there a good method to estimate the Miller capacitance of a triode strapped pentode? __________________ http://diyaudio.ecp.cc

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13th January 2009, 01:43 AM	#2
ray_moth diyAudio Moderator Emeritus Join Date: Jan 2004 Location: Jakarta	It makes sense for it to be Cg1g2 X stage gain. I'm guessing that the plate is too far from g1 for there to be a significant capacitance between them, but I could be wrong.

13th January 2009, 02:29 AM	#3
Poindexter diyAudio Member Join Date: Oct 2004 Location: Maui, Hawai'i, USA	That sounds right to me; after all, that's the idea of a tetrode in de foist place, no?  The problem would be to find this capacitance.  The datasheets very seldom give such data for trioded pentodes; we're lucky to get plate curves. I wonder, would this spec have to be tested for on a hot tube in-circuit, or could we just stick an LCR meter on the appropriate pins on a cold tube sitting on the bench? Aloha, Poinz AudioTropic

13th January 2009, 05:27 AM	#4
ray_moth diyAudio Moderator Emeritus Join Date: Jan 2004 Location: Jakarta	Hi Ponz, I don't see why the tube has to be hot to get this measurement. Temperature would make a difference, I suppose, but it should be slight.

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