Clipsal you make some interesting observations and I would say that what people hear by swapping tubes must be more system dependent than anything. I wouldn't want to give the impression that different 6SN7 VT231's don't make a difference, they most certainly do but I found the differences subtle relative to each other. The Ken Rads did provide fuller bass but not better and I take issue with the fact I have tried 3 pair and haven't been satisfied, they were all too noisey. I also felt they were a tad too rich in the mids but I suppose I find this more a taste/synergy issue than anything else.
My point is I have heard much more significant differences with tubes in other designs I have owned over the years. This pre-amp is so intrinsically good that so far as the 6SN7 goes I haven't found the variety I've used to make a significant enough difference to rationalize spending the money on some of these tubes. Of all I have tried I prefer on balance the Sylvanias and National Unions with the Ken Rads my least favorite, good ones are hard to come by I suppose.
The regulator tubes I didn't find to alter the tonality so much as enhance dynamics, presence and bass. This may of course be system dependent as well. To me the 6f6g was most significant, a real eye opener. I agree that the stock tubes were not nearly as good as all the tubes I've tried but changing the regulators should provide an interesting result, you should definitely give it a try and tell us what you think.
My point is I have heard much more significant differences with tubes in other designs I have owned over the years. This pre-amp is so intrinsically good that so far as the 6SN7 goes I haven't found the variety I've used to make a significant enough difference to rationalize spending the money on some of these tubes. Of all I have tried I prefer on balance the Sylvanias and National Unions with the Ken Rads my least favorite, good ones are hard to come by I suppose.
The regulator tubes I didn't find to alter the tonality so much as enhance dynamics, presence and bass. This may of course be system dependent as well. To me the 6f6g was most significant, a real eye opener. I agree that the stock tubes were not nearly as good as all the tubes I've tried but changing the regulators should provide an interesting result, you should definitely give it a try and tell us what you think.