Louis, You’ve got the right idea, for MC, but the wrong correspondence between db of gain and resistance. The values are stated in reverse order in the review, gain vs resistance. I think it would be as follows:
62 db gain = 278 Ohms = 13X gain
66 db gain = 117 Ohms = 20X
68 db gain = 69 Ohms = 26X
72 db gain = 29 Ohms = 40X
In other words, as gain goes up, resistance goes down, because you are using transformers with increasingly higher turns ratios to get more gain.
For MM, I would guess the MM inputs bypass all of the 4 permalloy SUTs and end up with the 40db total gain that is inherent to the RIAA section (adequate for most MMs, perhaps a little low for some MI types). Also, since the impedance seen is equal to the value of the static load resistor divided by the square of the turns ratio, for MC, we can extrapolate back using any of the above set of data points to get the value of the load resistor seen by the MM cartridge (and also at the secondaries of each of the 4 SUTs), which would be 47K ohms, as predicted and as is typical.
(For 40X gain, that means the turns ratio is 1:40. The square of 40 is 1600. 47K divided by 1600 is 29 ohms, as shown above.)
62 db gain = 278 Ohms = 13X gain
66 db gain = 117 Ohms = 20X
68 db gain = 69 Ohms = 26X
72 db gain = 29 Ohms = 40X
In other words, as gain goes up, resistance goes down, because you are using transformers with increasingly higher turns ratios to get more gain.
For MM, I would guess the MM inputs bypass all of the 4 permalloy SUTs and end up with the 40db total gain that is inherent to the RIAA section (adequate for most MMs, perhaps a little low for some MI types). Also, since the impedance seen is equal to the value of the static load resistor divided by the square of the turns ratio, for MC, we can extrapolate back using any of the above set of data points to get the value of the load resistor seen by the MM cartridge (and also at the secondaries of each of the 4 SUTs), which would be 47K ohms, as predicted and as is typical.
(For 40X gain, that means the turns ratio is 1:40. The square of 40 is 1600. 47K divided by 1600 is 29 ohms, as shown above.)