I was using a 502A until recently. For power tubes, I had great luck with the JJ Tesla KT-88s. Nice fat, warm sound. For the 12AX7s, the NOS Telefunken smooth plates are awesome - but expensive. For my 12AT7s, I used NOS Sylvania with gold feet - not that pricey, but great. Personally, I would go with new tubes for the power tubes and NOS for the preamp tubes - best of both worlds - great sonics and reliability.