suggestions for 6cg7/6fq7 preamp tubes


i have a rca and a sylvania in preamp now,sounds good except for a slight grain up top,,anybody famillier with these tubes?
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rca clear top is certainly one of the best, esp. the USA made ones.
thanks Ed!!
i visited a web site where they sold tubes that are "low noise"only 10% of the tubes they test make it to this catagory,is it worth the extra money to go low noise matched tubes?