I just got a new Marshall JVM410H (I bought it after reading many comments on this forum...bold move, but I love this amp!) The stock preamp tubes are all chinese, but surprisingly, the ones in V1, V2 and V5 are labeled 00067 and look shiny inside, while the ones on V3 and V4 appear to be your regular gray plate Shuguang and are marked 00054. I pulled them all out and installed new Tung Sol 12Ax7s. Immediately i noticed a much lower volume. After replacing the tubes one by one, I found V3 was the culprit. Put back the original and all was fine. So, I replaced that again with the Tung Sol that was in V1 and put a Mesa SPAX7 in that slot. Much to my surprise, after a while I noticed the volume drop again. went directly to V3, pulled the second Tung Sol and put the original back...all was fine again. I thought, man, two Tung Sols went busted at the same spot...so I tried again...and installed in V3 the other Tung sol I had in V2 (rembeber, this was working fine) and after a while...kaboom again. So...my new JVM ate 3 new Tung sols that were installed in V3...my question: Why V3 is eating up the tung sols? what's different here? I remember my VOX AC30CC2 had Tung Sols in V1 and V3, but used a normal chinese in V2 cause they said a more rugged tube was needed there...what's up with that?