Replacement Tubes for Marsh P2000T

Does anybody know what kind of tubes this preamp uses? Are they of the 6JD8/6922 variety? Please help!
5687s tubes
I have a pair of RCA Bronze Plate 5687 that I bought from Upscale Audio for about $30 (I think). They sounds very sweet to my ears and a definite, noticeable upgrade from the stock Jan Philips.
I use Tung Sol, they are more rounded, detail, and less noise then the National 5687 that came with them.