After all my tube rolling, I have found the Amperex USA 7308 PQ White Label (60's vintage) and the Siemens 6922 A-Frame (also 60's vintage) offer the most compelling sounds from the Herron. The Amperex are my overall favorites. They provide a warmish tonal balance, with very clean but not etched high end, deep tuneful bass and a warm, slightly forward midrange that tends to put soloists and vocals at the speaker plane or slightly forward. The information from behind the plane of the speakers tends to be "ambient". This is in contrast to the Siemens A-frames, that provide a somewhat wider soundstage, and a slightly more recessed bubble. Vocals are a tad lighter but still very natural. Overall tonal balance is a bit more neutral than the Amperex, but deep subterranean bass still manages to impress. The Amperex's have more heft in the mid and upper bass regions. Which works best ultimately depends on the rest of the system, I'm sure.
I have begun experimenting with combining these tubes to try for the best of both. My current setup places the Amperex in the Gain locations (1/4) and the Siemens in 3/6. The benefit over an "all-Amperex" setup is the widening of the soundstage and placing a good bit of the performance behind the plane of my Magnepans. Keeping the Amperex' in the gain spots holds on to their warm balance and plucky bass.
Both these tubes get the highs and the space right, which the EH tubes dont seem to do. As such, the EH (even the premium gold-pinned versions)have never been able to provide the palpable space and transparency I have obtained from these special tubes. I have tried other NOS tubes, including later vintage Siemens, and Amperex Hollands and USN-CEP's, but never quite got the seamless magic I'm getting from these 2 gems. I'm sure something is out there, but at some point ya gotta stop and smell the roses!
By the way, the middle (2/5) tubes are used in the phase reversal circuit. Since I accomplish this on my SACD player, I tend not to use the selector on my Herron. Since the Herron brings a new set of tubes into the equation for phase reversal, its not the ideal "objective" way to hear the effect. I keep Amperex's in the 2/5 spots. Keith Herron informed me they are barely in the signal path when the phase reversal switch is not engaged.
