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In Reply to: RE: ratio for interstage posted by Tubenstein on May 14, 2016 at 13:06:16
Both have a 1:1 turns ratio.I've never fully understood the impedance ratings of transformers.
Transformers don't really have impedance. They have winding ratios.
The impedance ratio is the square of the winding ratio.
So for a step up or step down transformer the reflected primary impedance is the load impedance times the impedance ratio.
The primary inductance has to be high enough to keep the inductive reactance high enough to "stay out of the way" to the lowest frequency of interest.
The shunt capacitance has to be low in value, low enough to keep the capacitive reactance high enough to "stay out of the way" to the highest frequency of interest.
I guess the impedance rating of a transformer has something to do with that. That is to say, the impedance the transformers were made to work with.
I would think that would have to do with the output impedance of your driver stage.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 05/14/16 05/14/16 05/14/16Follow Ups:
Same here, impedance ratings of transformers are supposed to represent the load they're designed for. But then, people use ITs to drive a grid that has a virtually infinite Z. How can a transformer designed for a 10K or 20K load exhibit a flat response with no load to swamp the inter-winding capacitance and resultant internal resonance(s)? Then there's the inductive reactance that you mentioned, which should be at least five times greater than the operating Z of the circuit to prevent acting like a shunt. Simply put, it appears to me that a 5K:5K transformer must be terminated with a 5K resistive load if it is to meet the manufacturer's specs.
--------------------------
Buy Chinese. Bury freedom.
If a device is sold as a 1:1 turns ratio, the 3k or 5kohm rating must be a nominal value dictated by the devices inductive loading at low freq. ? JH
Sorry for misleading you! Actually what I want to ask whether 5K or 3K load is what the 6EM7 loves to see.
Thanks!
If the only concern was the 6EM7 then the higher the load impedance the better.
But transformers have needs too.
I know that if you drive a transformer with a source impedance that is too low it can lead to ringing in the transformer.
You might want to ask Mike over at the MagnaQuest forum about this.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
You will get a much better recommendation from the transformer manufacturer, since the details depend heavily on how it is wound.
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