How expensive are best NOS tubes ? And how difficult to find ?

When I had an Octave V70se and later the V110 I tried a lot of different input - splitter  and power tubes. I always preferred the sound of vintage/out of production tubes. With some the difference in sound was huge and in others not so much. As far as NOS who really knows if they really are NOS or used.

That said I started with Dyn C1 sig speakers. My favorite tube was the original TS 6550 black plate followed closely by the solid grey plate. With those the little Mullards were a great compliment. Then I got the V110 and hated the Russian KT120's. The old TS were still my favorite. I also tried some British Gec KT88's. Didn't really care for those but not bad. Jim McShane told me about Ei KT90's but he wouldn't sell me any. When I first found some here on the Agon I bought them. These IMO were very good and at the time pretty reasonable. Then I upgraded the Dyn C1's to Raidho D1's. Now I didn't care for the TS 6550 or the little Mullards. KT120's sounded a bit better but still not good. The Gec KT88's and Ei KT90's were the tubes that sounded best with the D1's.

My point is all tubes have a sound signature that will vary with manufacturers (not always labels for they may be only one manufacturer that makes many labels).

Different tubes with different sound signature. Different coloration ?

Inna
yea probably some coloration trades taking place like swapping boutique capacitor, resisters, etc.....
i was thinking a nice CA or WA red wine....
but the French gotta eat too

But for me, unless too much, better this kind of coloration than 'coloration by omission '
done by transistor amps.

Another vote for Vintage Tube Services !!! Andy is great to deal with and is also super knowledgeable.