I have these tubes new onhand: Tube Store 7025 preferred. (1) Sovtek 12AX7LPS (Russia) (2) Tung Sol 12AX7 (Russia) (1) JJ ECC83S (Slovak Republic) (2) Can someone please help me with these tube question: 1. Where is the Tube Store 7025 made, what tube, if any, is it modeled after, and how does it sound in general. 2. What is your opinion of these four tubes in terms of tone and reliability. 3. Please suggest a starting point for retubbing a KOCH Studiotone. There are only three preamp tubes used in this amp. I understand where V1 is and basically what it does. But I don't really know much about the function of the other two preamp tubes. (They are all 12AX7). Power Tubes in there now are TAD EL84-STR's with about five hours on them. I'd rather do this one time, as I find it difficult to install these tubes behind the power tubes and its screen (there to prevent breakage and such). The preamp tubes in there now are about five or more years old and I am getting some intermittent hum, which was there before I put in the new EL84s. Normally, this amp runs silent. Thank you.