I also have the PH3SE. In my opinion the bugle boys will sound much better than the stock ARC tubes and to my ears they will also sound better than the mullards overall.(mullards will have a little more bass)
I'm currently using 6h23 russian tubes which are very good before that I used amperex 7308's which were also very good but I liked the 6h23's more.
I'm currently using 6h23 russian tubes which are very good before that I used amperex 7308's which were also very good but I liked the 6h23's more.