Got my preamp tubes from Tube Depot today! That was fast via USPS. I put the 5751 in V1. One thing that struck me is that it became even quieter and it wasn't noisy to begin with. Some of the shrill/ragged high end is gone. I guess JJs are the way to go with Jet City amphs, at least to my ears. I don't know how much the 5751 really affected things. I guess I'll have to put my spare 12AX7 in there and see what the difference is. Seems to have made a good amph even better.