The U52 rectifier which is what I use in the PX25, yes there would be issues. But the circuit designed by KS with 5U4G - no issues at all. The U52 sometimes has an issue with the 300B, so we changed the tube complement accordingly.
Thanks, John. What are the drop in replacements for this 5U4G in this circuit? I have a sizable collection of rectifiers -- 5AR4, 5R4GY -- assembled, in part, for my H3000. Will they also work in the M-2500?