My prototype K&K Audio phono pre and Line Stage use a total of six 6H30s. These tubes are configured as diff. pairs with current source tails and CT transformer loads. Since the Lundahl LL1689 transformers will tolerate only a small amount of DC current the 6N30 tubes need to be matched for plate current at the OP. None of the tube dealers will do this and unfortunately my friend Kevin Carter of K&K has passed away. So I bought four ARC select tubes from Upscale and three of them met my specs. So I ordered twelve more with the same yield. As a result I have twelve tubes I can use and four that need a new home.
ARC Select Worth Price?
Sovtek 6H30Ps are sounding woolly. Upscale offers replacement quads (apparently not matched) in various grades up to ARC Select cryo, all priced accordingly. (I have not inquired directly with ARC).
My only past experience is with 6SN7s, which can be rolled infinitely. What would veterans buy, and from whom?