Has anyone compared the EMT 139st phonostage to others ?

Wow! What a wealth of information from Good Music. I will never own an EMT anything (not because I don’t like the company but just due to my own old age and set preferences), but the historical perspective GM conveyed is very interesting. I am left with one question and one opinion.

Question: Why and how do you use two SUTs per channel?

Opinion: A 12AX7 or any tube that closely resembles the 12AX7 in its parameters (very high mu, very high plate resistance, very low current capacity) is a bad choice for a cathode follower. Because such a CF will have a relatively high output impedance and a low current carrying capacity, and it is after all the job of a CF to convert a voltage to current in the process of lowering output Z. In other words, the 12AX7 is not a good driver tube. I do realize it has been done by companies other than EMT, or the various persons that make their built in phono stages, and it may sound great.

There is an Audiogon listing of the TPM-1000 transformers.

One one picture the explanation is given.

I can't upload pictures here a simple explanation:

- both 100% identical transformers are connected in series. (which means input impedance is doubled but this has no effect on soundquality at all)

- the core of both transformers are oriented 90 degrees to each other (hum elimination, once can even do it by ear and hear the difference)

So if they’re in series, then the net voltage gain is a multiple of the individual voltage gain of each SUT? For example, a 1:10 ratio will increase gain 10X at the secondary of the first SUT. Then that voltage would be again increased by 10X across the second SUT, for a total V gain of 100X? Why would that ever be needed? I must misunderstand the hookup.

What would that result in an increase gain of 10x ?

It is a normal series connection, it increases the input impedance!