I'm new to Step Up Transformers

@rmcfee

I am quite familiar with both the Zesto and the Paua.

The Paua needs to see a load of at least 470ohms.

I fiound with my sample the optimum load at 1000 ohms.

I would strongly suggest you try on the moving coil input on the Zesto both the high and low MC input settings and both the 400 ohm and 1000ohm settings to find the best combination.

If you try an external SUT you must ensure that the SUT has a maximum turns ratio of 1:10 to be sure the Paua is loaded at a minimum of 470 ohms.

The Herron phono stage, now out of production but possibly available pre-owned, is another that achieves high gain with an FET based input stage followed by an all tube circuit. It was very highly regarded, one might say venerated, by some who frequent this site, before Herron closed down.

Isn't the Soundsmith Paua a moving iron cartridge? That's the mechanism used by Grado and some others. No SUT required.

I checked and the Paua is indeed a moving iron cartridge like all the others in the Soundsmith line. 

It is moving iron, but it has a .4 Mv output.  

The approach of using a hybrid transistor and tube to supply the needed gain for low output cartridges is to reduce the level of noise from using tubes exclusively.   

The use of a SUT also reduces noise as an issue and adds the sonic signature of a transformer.  If you want tube only amplification (no transistor stage or no SUT) you have far few alternatives.  I mentioned Aesthetix earlier as an all-tube design that sounds good (if a bit noisy); another good sounding example is made by Lector (quiet for an all-tube design).