I tested many thousands of tubes, including 6N6P and 6N30P and I'd like to clarify few things about replacing 6N30P with 6N6P:
- all 6N6P (in russian 6?6?) have gold pated grid;
- 6N6P is not perfect equivalent with 6N30P; 6N30P has higher plate current, higher heater current, higher gm but lower gain (gain is gm x Rp and Rp is lower);
- tubes have the same pin out and isn't any risk when we insert 6N6P as replacement for 6N30P;
- matched quads of double tubes are very rare, from a batch of double tubes about 30% are unbalanced, from the balanced ones must be found 4 tubes (8 internal triodes) with the same plate current and gm); of course, depends the tolerance used for matching, I use max 5%, if is used 15% will result more quads;
- I made this replacement in few CDs, preamps and amps with excellent results;
- anyone must try this replacement, nothing to loose, and the best selected 6N6P quad costs less that one NOOS 6N30P-DR;
- the best sound is met at 6N6P from 70's;
- old FOTON 6N6P have generally a better sound but not as replacement for 6N30P, those FOTON are usually weak tubes and not suitable to replace 6nn30 that is powerful;
- best matching is made by curves, next is by Ip and Gm, only by Ip or only by gm is not real matching;
- for preamplifier tubes matching by gain is a good compromise, better than untested or unmatched
In photo can be seen a wonderful pair matched by curves.
