Selecting an IT impedance

Steven-H · 22nd January 2008, 09:16 PM

All,
What parameters do I look for when selecting an Interstage Transformer ? Mainly; I am unclear on how to select the secondary...Wouldn't you normally want the lowest impedance possible to the grid of your tube ?
The Primary impedance I understand completely...

Thanks !
Steve

bambadoo · 22nd January 2008, 09:35 PM

Maybe this thread is helpful?

http://www.thaiavclub.org/forums/ind...sg%25msg_id%25

Steven-H · 23rd January 2008, 06:12 PM

That helps a bit; but I am very curious as to the selection of the secondary impedance value. Again; I would think you would want the lowest possible value to drive your grid ?

Thanks,
Steve

Wavebourn · 23rd January 2008, 06:16 PM

The highest with Miller capacitance in mind, unless you need a grid current.

Steven-H · 23rd January 2008, 06:46 PM

Sir,
Thanks - but I am not quite sure how I need to compute this; as all I have would be the grid impedance value ?

Regards,
Steve

Wavebourn · 23rd January 2008, 07:04 PM

Assume it as a capacitive load.

schiller · 23rd January 2008, 10:54 PM

Hi, i think this impedance ratings for the secondary are only missleading for the purpose of using the IT to drive a tube.

Don't care about this, you need to know what is the anode impedance of the driver tube and see if the primary inductance is sufficient.
Unless you are driving A2 grids, i see no reason for stepdown IT, so turns ratio should be 1:1.

The driving impedance is the driver's impedance + the dc resistances of the windings.

If your driver of choice is e.g. an 6SN7, you can forget linear response down to 20Hz. Needed primary inductance is too high. Maintaining this would compromise linearity in the higher frequencies

Greetings
Konstantinos

22nd January 2008, 09:16 PM	#1
Steven-H diyAudio Member Join Date: Jan 2007 Location: The 1st State	Selecting an IT impedance All, What parameters do I look for when selecting an Interstage Transformer ? Mainly; I am unclear on how to select the secondary...Wouldn't you normally want the lowest impedance possible to the grid of your tube ? The Primary impedance I understand completely... Thanks ! Steve

23rd January 2008, 06:16 PM	#4
Wavebourn diyAudio Member Join Date: Sep 2006 Location: Pleasant Hill, CA	The highest with Miller capacitance in mind, unless you need a grid current. __________________ The devil is not so terrible as his mathematical model! Wavebourn: We Create Creativity!

23rd January 2008, 07:04 PM	#6
Wavebourn diyAudio Member Join Date: Sep 2006 Location: Pleasant Hill, CA	Assume it as a capacitive load. __________________ The devil is not so terrible as his mathematical model! Wavebourn: We Create Creativity!

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22nd January 2008, 09:35 PM	#2
bambadoo diyAudio Member Join Date: Feb 2003 Location: West Coast of Norway	Maybe this thread is helpful? http://www.thaiavclub.org/forums/ind...sg%25msg_id%25

23rd January 2008, 06:12 PM	#3
Steven-H diyAudio Member Join Date: Jan 2007 Location: The 1st State	That helps a bit; but I am very curious as to the selection of the secondary impedance value. Again; I would think you would want the lowest possible value to drive your grid ? Thanks, Steve

23rd January 2008, 06:46 PM	#5
Steven-H diyAudio Member Join Date: Jan 2007 Location: The 1st State	Sir, Thanks - but I am not quite sure how I need to compute this; as all I have would be the grid impedance value ? Regards, Steve

23rd January 2008, 10:54 PM	#7
schiller diyAudio Member Join Date: Jan 2005 Location: Athens	Hi, i think this impedance ratings for the secondary are only missleading for the purpose of using the IT to drive a tube. Don't care about this, you need to know what is the anode impedance of the driver tube and see if the primary inductance is sufficient. Unless you are driving A2 grids, i see no reason for stepdown IT, so turns ratio should be 1:1. The driving impedance is the driver's impedance + the dc resistances of the windings. If your driver of choice is e.g. an 6SN7, you can forget linear response down to 20Hz. Needed primary inductance is too high. Maintaining this would compromise linearity in the higher frequencies Greetings Konstantinos

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