My suggestion to the OP, if you are spinning lots of vinyl through a 500C, is to invest well in the phono stage tubes.
For as common a tube as a 12AX7, you will be surprised to find that modestly-priced domestic used/strong stock often substantially outperforms the new production, and is often very quiet even in standard 12AX7 types. They are still so plentiful, I still have no need for new production.
Shoot for organ pulls, which are often low-hours, and are specially tested and graded quieter and tighter matched than normal. People will sell them by the bucket from a retired Lowrey or Hammond when grandma passes. You can stumble on beautiful Raytheon or RCA BPs for peanuts if you are patient.
A pair of late 50's to early 60's US black plates, judiciously placed, can work wonders in that receiver. Nothing new will touch it for timbre and tonal nuance.
Another somewhat rarer tube that does really well in these, and is still relatively inexpensive, is the CBS 7025. The CBS has a unique dot etching, similar to, but not the same as a GE. And it sounds far more alive than your typical GE long grey plate. Older CBS 12AX7s are Hytrons and are also an excellent tube. I'll take the CBS over the later production long grey and 14mm RCAs, all else being equal. But they are rare.
I won't take you further into the world of tube exotica, other than to reiterate that used/strong old US production is still a terrific bargain. Once you start looking at the old Europeans, it gets expensive quickly, and you have to be careful; it is easy to get fleeced.
The C series is a very nice platform for rolling, especially in the tone amp stages.
