The newer transformers may have a lower inherent resistance/impedance. I don't know about old vs. new pole mounted, but for sure, pad mounted transformers tend to have much lower impedance, so much that the recommended AIR for service breakers may be higher if you have a pad mounted transformer than pole and are a short distance from the transformer.
New Transformer on the Pole
So, I got home yesterday and my wife told me that the power was out for a few hours while the town electrical department replaced the transformer on the pole across the street. I looked outside the window and saw the new transformer--much different (nicer, more modern) looking that the old one that I've been looking at for years. You know what I'm wondering......
So, last night I got a chance to fire up the rig and do some listening and I have to tell you that I heard some noticeable improvement in the sound. The background was "blacker" and there was a bit more purity and dimensionality. Am I just imagining this or could a "transformer upgrade" really deliver sonic gains?