Elizabeth -- Which version is it? I did some quick checking, and the X10v3 uses a pair of 6112's, while the X10-D uses a pair of ECC88's (which are equivalent to 6DJ8's).
Both tubes are available for reasonable prices from vacuumtubesinc.com and tubesandmore.com, and undoubtedly from many other sellers of nos and vintage tubes.
However, I gather that at least in the case of the v3 physically accessing and changing the tubes may not be particularly easy, although it is probably do-able. It was apparently designed with the expectation that the tubes would either never require replacement, or be replaced by the factory.
The 6112 was designed for military use, and I saw a comment indicating that its rated life is 100,000 hours.
Best regards,
-- Al
Both tubes are available for reasonable prices from vacuumtubesinc.com and tubesandmore.com, and undoubtedly from many other sellers of nos and vintage tubes.
However, I gather that at least in the case of the v3 physically accessing and changing the tubes may not be particularly easy, although it is probably do-able. It was apparently designed with the expectation that the tubes would either never require replacement, or be replaced by the factory.
The 6112 was designed for military use, and I saw a comment indicating that its rated life is 100,000 hours.
Best regards,
-- Al