"The old green Altec 4722 input transformers are very nice MC step-ups. They are a bit expensive now, used to pay around $35 ea for them, but they are an excellent transformer.
You should have invested in Altecs. LOL. Prices are on the move. Looks like singles are going for a couple of Ben Franklins, with assembled duals (wired can and RCA plugs) going for upwards of 800 dollars. New production Jensens/Lundahls are in that ballpark. Homemade is the way to go, if you know how.
Even so, those prices are bargain basement compared to some transformers being advertised, out and about. I remember back in the day, when Mitch Cotter blew the doors off the audio world with his own style of Mark "I never met a preamp that was too expensive" Levinsonesque pricing. That was 40 years ago. But everyone liked his blue box, and, since then, no one has batted an analog eye over through the roof pricing.
I recently checked out a reviewer discussing MC step ups. I've edited out the brands, to protect the innocent. Here are a few quotes, offered just for fun. It's like reading wine reviews. Or even now, beer reviews. I never hear any of this stuff, but I wouldn't mind a beer, or a glass of wine with my music, occasionally:
It lacks the immediacy, transparency, (inner an outer) detail, purity, speed and low sound-floor...
It was clean, smooth, quiet and detailed. It was especially impressive in the high frequencies, with extraordinary extension...
There is a noticeable "drying" ... You hear less definition, natural texture, "air" and "harmonics" developing and decaying. There is also a slight reduction of image size and focus; musicians are a little diffuse sounding.
The "timing" ... is good, but it is not quite as precise as the XXX, so the music isn't quite as intelligible...
The high frequencies are also good, being smooth and clean, but there is a sense of a "rounding" of the tiny details which individualize music. This may be caused by either a roll-off or a subtraction of low-level harmonics (and other musical information) or both. One other problem is that this model doesn't have the dynamic "jump" or "shock"...
PS: I think these subjective reviewers, the one's who can hear all this stuff, out of principle, ought to post their hearing test audiogram, updated once a year, in order to show readers just how golden their hearing really is. Fat chance that will ever happen.