Probably a typo on Swampwalker's part, but the tube is a 6CG7/6FQ7. It is not a 6FG7, which does exist, but I don't think is a drop in replacement for the former.
Inexpensive: read roughly $10-20/tube for good stuff. I've liked the GE's and JAN. There is one oddball tube I rolled that I cannot put my finger on right now that also was quite good. As I said, their a pretty common and not at all exotic tube. The differences in my amp, and those in your amp will not likely be the same. You should just get a few pairs and listen for yourself. I haven't found there to be as much of a difference in the NOS tubes of this type, than those in the very covetted, overused, much inflated, sometimes counterfitted 6922/ECC88 family. If your amp used those you'd be in for a roller coaster ride.
Marco
Inexpensive: read roughly $10-20/tube for good stuff. I've liked the GE's and JAN. There is one oddball tube I rolled that I cannot put my finger on right now that also was quite good. As I said, their a pretty common and not at all exotic tube. The differences in my amp, and those in your amp will not likely be the same. You should just get a few pairs and listen for yourself. I haven't found there to be as much of a difference in the NOS tubes of this type, than those in the very covetted, overused, much inflated, sometimes counterfitted 6922/ECC88 family. If your amp used those you'd be in for a roller coaster ride.
Marco