K&K Audio / Lundahl Transformers

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Original Message

Interstage Coupling Calculations

Posted by Slick on September 12, 2007 at 20:16:57:
Sorry, this must seem very basic, but how do I determine the load on the plate of a tube when using, say a LL1635 as a plate load/coupling transformer (for a phono stage output)? I have been told that the impedance of the primary is equal to 2*pi*F*L . If this is so (and it sure seems correct), how does the load from the secondary, in this case the line stage attenuator, figure into the mix. Is it the resistance times the turns ratio squared; that value in parallel with the primary impedance? If so, would adding a secondary shunt resistance linearize the output in the bass region? I'm worried about rolloff in the lower frequency ranges where the primary impedance is decreasing and therefore the stage gain is decreasing.
My plan for a second phono stage (after the all-in-one passive RIAA) is to use a direct coupled common cathode amplifier with a SS current source in the tail. So the first plate would go directly to B+ and the second would have the 1635 as the plate load.
Thanks in advance for your help.

Slick

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