Rgd,
Victor can recommend some good dealers for you. Joseph and Victor both prefer the sound of Siemens CCa in this preamp, however, one owner that gave a testimonial in Joseph's web site liked some NOS Amperex. The preamp comes stock with EH( Electro Harmonix) tubes, which sound very good in Joseph's excellent circuit. Joseph's upgrade is, I believe, a 70's Siemens E88cc, which will give you a little better sonic picture. The ultimate tube for this preamp is an early 60's Siemens CCa, but they are getting rarer and very expensive. One nice thing to consider is that there are only four tubes in the preamp, and basically only two of them which are fairly critical in the audio signal path( tube locations 1 and 3 ). I was able to find a good pair of Siemens Cca for these locations and am using some late 60's,early 70's Siemens E88cc in locations 2 and 4. My recommendation is that when you get your new preamp, allow it to warm up for a few days to break in the preamp and get an idea of how it sounds in your system. You might just like it so much with the stock tubes that upgrading might become an alternative that you can wait on for a while. I lived with my stock preamp very happily for a few months before I got the urge to try some upgraded tubes in location 1 and 3. I hope you enjoy the preamp as well as I do. Happy Listening.