Hello...I purchased my JCM 800 (serial#02726N) back in the Fall of 1981. I pulled the rear plate off the head for the first time so I could install new tubes for the first time. I expected to find four EL84's, but was totally surprised to find 2 KT66's, and 2 6L6GC's instead. Is this normal? The amp sounded totally different from other Marshalls I was exposed to, now I know why. Did Marshall do this often, or did they just run out of specific tubes and slap in whatever they had on hand. It's kinda hard to believe they did that as the KT66's require an entirely different transformer than the EL34's. Any comments or logical explainations?? Thanks.