The CS600 can run a variety of tubes from the 6L6 and EL34 families by varying the positions of the cathode & plate switches. In the 6L6 family, there are the aforementioned 6L6GC, the 6L6WGB, the 6L6GB, the KT66 and the 350B. In the EL34 family the there is the EL34 and the KT77. In addition 6550 and KT88 tubes (ditto for the 350B) can be used if you leave the top cover off to allow for the tubes taller height.
Good condition. No box.