Selecting an IT impedance

[Steven-H]

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]

Maybe this thread is helpful?

http://www.thaiavclub.org/forums/index.php?topic=4314.msg%msg_id%

 

[Steven-H]

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]

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

 

[Steven-H]

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]

Assume it as a capacitive load.

 

[schiller]

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