Outlier - preamps seem to be more sensitive to tube quality than amplifiers. A tube which sounds perfect in an amp can squeak and be rather noisy in a preamp. Be aware of this when shopping. Ask the seller if they honor an exchange or refund if the tubes you buy are too noisy for the Supratek.
I've tried many 6SN7's and clearly the best are either the Ken Rad black glass or the Sylvania 6SN7w's (metal base).
The RCA 5692 red base tubes you speak of are just okay. Tung Sol Round plates are pretty good. Raytheon VT231's are alright. Brimars are too detailed but may work in some situations. A tube I haven't tried is the Mullard CV181 - which isn't a "true" 6SN7 but should work.
In your tube quest you might try looking/shopping for 6SN7GTB tubes. They are new(er) cost MUCH less and there are quite a few different brands available. So far, I've picked up some National's and a pair of Canadian made GE 6SN7GTB's which were pretty darn good. There is no doubt that the character of the older NOS tubes is superior to the 6SN7GTB's I've tried but the GTB's are WAY quieter, less microphonic and super cheap (can usually be purchased for 10 or 15 bucks a pair).
hope this helps.
I've tried many 6SN7's and clearly the best are either the Ken Rad black glass or the Sylvania 6SN7w's (metal base).
The RCA 5692 red base tubes you speak of are just okay. Tung Sol Round plates are pretty good. Raytheon VT231's are alright. Brimars are too detailed but may work in some situations. A tube I haven't tried is the Mullard CV181 - which isn't a "true" 6SN7 but should work.
In your tube quest you might try looking/shopping for 6SN7GTB tubes. They are new(er) cost MUCH less and there are quite a few different brands available. So far, I've picked up some National's and a pair of Canadian made GE 6SN7GTB's which were pretty darn good. There is no doubt that the character of the older NOS tubes is superior to the 6SN7GTB's I've tried but the GTB's are WAY quieter, less microphonic and super cheap (can usually be purchased for 10 or 15 bucks a pair).
hope this helps.