I finished building my Moreplay last week and have been enjoying it greatly: frankly, it's amazing to hear how good such a simple circuit can sound. I was dubious of Doc's claim (earlier this summer) that the Moreplay sounded better than an Extended Foreplay III (which has been my preamp for the past 15 years), but he's right.
I have a question: tube rolling 6V6s, I find that one pair (RCA 6V6GTs from the '50s) measured exactly 125 volts on each plate (to ground) and 8 volts on each cathode (again to ground). But a pair of Sylvania 6v6Gs (from the '40s, I suspect) measured 135 and 143 volts on the plates and a bit less than 8v on the cathodes.
These readings are within 10-20% of the specified measurements, so I'm not concerned about anything burning up (and I don't hear a volume imbalance between channels), but I do wonder if there are sonic advantages to keeping more closely to 125 volts on the plates. I could, for example, reduce the value of the cathode resistors and put 1K pots in series with them, and this would allow me to adjust the plate voltages very accurately. Would this be worth doing?
I know matching power tubes is important when they're run push-pull and you want to run them hot but avoid excessive plate dissipation, but is there an advantage to matching tubes beyond that? After all, circuit designers take care to choose particular operating points, but tubes are notoriously all over the place in terms of transconductance and how much current they draw at idle. As I understand it, this is just an unavoidable consequence of tube manufacturing A tube can test "good" but still measure "high"or "low" once put into a particular circuit.
