For this test I wound a transformer matching the one I posted about earlier. It has 3500T : 500T. I expect it to perform similiar to this one.
For a comparison I wound one with 1000T : 100T. Then I bread boarded this test jig.
The one thing to remember is that the tail cannot wag the dog! No matter what the Z load is the Z input will only go as high as the inductance of the coil at the operating frequency so I establish the base line (start point) but checking the primary with no load. The 3500 : 500 read off the scale so I established the start point fo it at 19H with 490Ohm load. here are the results of the test.
1000 : 100
open circuit 4141mh
3500 : 500
The math says this is a 36 Henry primary. since my meter only goes to 20 Henry I loaded it to get 19 Henry with 490 Ohms. So the input impedance would be more than 48K for a load above 490 Ohms. The chart above says 25K : 500 Ohm so what's up with that?
The plate circuit is a voltage divider. The plate resistance in series with the primary will divide the voltage as the current swings. As plate resistance goes down and plate current go up the primary develops a voltage which oposes the change in current and induces an output in the secondary.