I got my Darkvoice yesterday and hooked it up today. I skipped the factory tubes and went straight to a Silvania Jan 5998 and a VT-231. The sound is beyond my expectations when used with the MassDrop HD6XX. I think this pairing was made for one another ! I don't have a hum with this combo of tubes ( I did with a TS 7236 installed) which is a relief. Overall money well spent.