Question for tube aficionados

Yes try NOS OS 5751s they were all the rage 10 years ago.  They are more reasonable these days.  I advise you get Sylvania blackplates, RCA easier to get and even GE again blackplate and their 5 star brand.  If your up to a search the Raytheon windmill getter 5751 is very good,  Get triple mica preferred over doubles.  Sylvania's Gold Brand and RCA Command series are worth looking for. Good Luck tube rolling is a slippery slope.it can be addictive, PM me for more advice/help.

The current production Gold Lions produce a sound that comes closer to the old production Philips tubes such as Mullard and even the less rich sounding Amperex.  Still many of the old 5751s while excellent in regard to tone are even better for imaging and sound spectrum profile balance  i.e. relative amounts treble to mid to bass that is partly a function of what a tube type can alter sort of a tone matter but different in my mind.  Gold lion does not make a 5751 to my knowledge but I sure would like to see them try. They do make a 12AU7.
There has been a run on whether a 6SN7 can be subbed for a dual triode 9 pin minature, and it can in some applications take the place of a 12AU7 in some applications. adapters can be bought on Ebay and elsewhere.  I am not sure whether you pre would allow the diferences betwen the 2 or not, but my understanding is that they serve similar purposes.  6SN7s are said to be very linearand there are plenty of 12AU7 bashers around on tube froums.