Jolida jd-502p

I would simply try them out. In virtually every instance that I rolled a 5751 in for a 12AX7 it worked. The different sonics may or may not appeal to you but I really like them. You may want to start with recent production NOS JAN 5751s from the 80s they shouldn't cost very much. It will give you an idea of what the better ones sound like. Have fun trying them out.

The 5751 is simply a lower gain version of the 12AX7. It will not do any harm in the circuit and is a direct replacement.

Like it better? Only you will be able to make that decission.

Thanks everyone for your responses. I did get a chance to
hear a pair of RCA JRC- 5751WA the sound was was nice and open with a good sound stage and nice separation but very little bass.In other peoples experience do the 5751's typically lack bass. Is there another tube that I might try to get a little more bass?

Try the GE TM gray plate 5751 from the 50s. The bass is prodigious in my experience and several friends as well. The Sylvania 2 mica Gray Plate 60s tube also has more bass than the RCA BP. As far as 12AX7s go you will prolly have to go with true Mullard Blackburn long plates "IF" you can get decent ones. They seem to emphasize bass. Failing that specific tube try any other older Mullard production.

Hi Wilson667

What 12AX7 or 5751 tubes did you get to replace the existing 12AX7 tubes in your JD-502p? Also is your JD-502P the stock or upgraded one from Jolida?

Thanks