Hi, markeetaux, I swapped out the stock Electro-Harmonix tubes from my JD9 with some Mullard style tubes from Groove Tubes. They're the GT-12AX7-M tubes. I noticed that the price has gone up quite a bit from when I bought them. They made a big improvement in the sound I got from the JD9 with both MM and LOMC cartridges. I tried some Chinese style Groove Tubes (GT-12AX7-C) and they were better but I prefer the GT12AX7-M tubes. The C style had great mid-range but I like the overall tonal balance and bass definition of the M style.
If you do a search for JD9 and Mullard style tubes you should find quite a few discussions about their sound compared to other tubes.
Regards,
Tom