On the MA-1 there is little space between the tubes. The other 6SN7s from S4A are not narrow either, so that will require trial and error. Ordered 4 pieces. I will also try them in the MP-1, although I am very satisfied with my old Foton's. I have struggled to find three ribbed anode versions from '51. I'm curious what the Linlai’s can say in return.
As far as I'm concerned, they're not going to leave our house until I'm dead. At least that's the plan. This applies at least as much to the MP-1. This is crucial for the sound of my entire set. On Monday, the baby will be transported home from Ralph again after an update. I used the pre of the Aurender for a while, but it really doesn't come close, not even a little, to the MP-1.
I don't know your pre-amp, but I have had the MP-1 for 16 years now and every time I enjoy the enormously wide and deep listening window, the high involvement, etc. I have not yet come across anything that suits me better, but to be honest, I I'm no longer looking for better. I now have an MP-3 from a friend that I am fitting with new tubes. This one is f...ing good in itself. In short, I have been hooked from day 1. I might give this a listen. I would like to invite you, but it's not nearby, so to speak.