i bought my 1999 Ampeg SVT-CL from someone inside the music community around me i thought i could trust, and in my fever to get the amp into my studio, did not open the back to check if all tubes were the same. i could only try the amp in the seller's studio with a single 15" cab. i had my doubts but bought it anyway after the guy confirmed it had been retubed a little over a year ago. as far as i understand "retube" should mean an entire matched set. he showed me the receipt, which lists 6 tubes at around $250, so i assumed he was correct and brought the amp home. days after running it with an ampeg 810 at 4 ohms i noticed difficultly keeping the bias lights green. the top left light would fade to red right after adjusting and eventually would stay lit. i experienced low volume and a distorted tone, and still do. this weekend i finally managed to get the amp to tech who removed the grill and immediately noticed two mismatched tubes, which leads me to believe the seller may have blown a couple and replaced them after the initial proper retube. since he sold it to me with the words "retube" and receipt shown confirmed, i feel cheated. he should have mentioned the two mismatched. now i've got a $200 retube on my hands. my questions is, how detrimental to the amp, [ and how quickly ] is it to just replace two tubes instead of the whole set?