tube upgrade for first sound

Try the Siemens CCa Gold Pin 7308 (as mentioned above) along with the Sovtek 0A2 as the other tube. Have them both Cryo'd, or purchase them already cryo'd.
The sound and dynamics will be improved.

I've very much enjoyed the Russian 6H23s I've tried from the Cable Company in my Audio Research SP9 Mk III preamp. They stomp the stock Sovteks into the ground. Worth a try.

I have some cryoed Telefunkens in my First Sound. The are fantastic - dead quiet and dynamic. Beautiful sounding tubes. I bought them from TubeWorld.com. They are costly but I really wanted the return policy if I did not find the performance justifying the price.

thanks for the suggestions. I have tried both the Russian NOS 6H23s and the Siemens gold pin 7308s since starting this post. The 6H23s are a nice improvement on the stock tubes. They are smoother and have a bigger soundstage, and I think they are a good value, but the Siemens took me to a new level! They are unbelieveably fast and transparent, much more low level detail, better width, depth, better placement from front to back, more natural voices----you get the idea. Unfortunately, they were obscenely expensive, but worth every penny to me. Now I understand why Emmanuel Go recommends them for his preamps.