DeadwaxI have the EQ500 and really enjoy it in my system. I initially replaced the rectifier with an early 60's NOS Mullard sourced from Brent Jessee. That alone had a notable impact, adding more weight to the sound. I picked up a pair of mid 50's Tele's from TubeWorld Express in WI to replace the 12AU7's but waited to roll them until I could also swap in some Tele 12AX7's as well. I ended up picking up some used (reportedly testing strong) Tele 12AX7's on USAM and proceeded to roll all 6 gain tubes. The result was disappointing, so I started a process of elimination to see which were the offending tubes - turns out they were the 12AX7's. So I'm now running the stock JJ's with Tele 12AU7's and a Mullard rectifier and love the sound - big improvement over stock. I'm in now hurry to replace the JJ 12AX7's but I do suspect that a quality NOS Tele quad would sound stellar.
Do you still have the EQ-500? I just purchased a used one and am shocked at the paucity of info and vagueness of the manual. So, the 12AX7's should all (4) be matched? How does loading work for a MC? Thanks!