I'm new to Step Up Transformers

Most tube-based phonostages either have built in step up transformers or expect the buyer to use his own step up transformer to supply enough gain.  The typical tube-based phono stage would need to add more tubes and would run the risk of excessive noise if they tried to supply the needed extra gain without using a step up transformer.

The extra gain needed for low output moving coil cartridges can more easily be supplied by solid state phonostages so they rarely include one in their design.  

I recently purchased a Zesto SUT for an EAT eglo petite tube hybrid MM/MC phono stage. The overall sound from the Rega Aphelion2 cart is fuller with the SUT with MM gain settings compared to without SUT and higher gain on PS. The SUT adds a bit of transformer hum, but cuts the tube hiss. This is not noticeable at normal listening levels, only when I put my ear right next to speakers with nothing playing.

I am also thinking about upgrading my PS, and given the various flavors of noise, I may tend towards a SS PS. No idea what kind yet. 

There are many fine quality tube based phono stages that offer sufficient gain for a LOMC cartridge and do not contain a step up transformer internally. Many of those use a solid state or hybrid gain stage in order to achieve that goal (Manley, probably ARC), but some even do it all with tubes (Atmasphere) and that can be done while preserving a good signal to noise ratio, contrary to what some will say. 

Aesthetix offers all-tube high gain phono stages which I like, but, they have more noise than most tube stages employing only tubes for active amplification.  Among my favorite tube phonostages are those made by Audio Note which require an additional step up transformer, Zanden (built in transformer), and Viva (built in transformer).  

  Thanks for all the responses -  it's great to have access to all the experience out there. 

    My Zestos does have a MC section - it has settings for Low Gain or High Gain. 

My confusion was because a friend with the same phono preamp as mine was telling me a SUT would improve the sound. And others online were saying similar things.