Have just under 100hrs on an Amperex USA 6922 gold pin HP label. Night and day compared to the stock tube. Like removing a blanket covering the speakers. Excellent imaging, airy open top end and lots of detail. Found it to be a bit harsh/grainy with some female voices, but turning down the volume on the DAC clears that up. It doesn't seem to like the same volume level as the DAC output if setting it up in that manner. Will try a Mullard made in Holland next.