Hi guys, I'm new here and have a question hopefully someone can help me with. I've had my MarkIV for a couple of years now, but I've only recently been playing with it since I got married and we've had 2 kids right after I acquired it. The head is a short version and I'm pretty sure it's one of the early (ver. A ?) heads since the power cord isn't removable. This is by far the best sounding amp I've ever had or played through. My JCM800 will be collecting some dust in the garage now 
Problem: About a month ago I changed out most of the preamp tubes. Some were noisy and I was also testing tonage. I changed v1 + v2 with MB spax7's and v3 + v4 with mullard reissue 12ax7's - high gain (from tubedepot.com). After I did that the lead channel had very little gain when running in Tweed mode. With both drive and gain pulled out and set around 8, it had a little more gain than rythm 1 and less than r2. However, the gain was fine in full power mode. After some messing w/ it I found that the problem was from the new spax7's in v1/v2. I put the original spax7 back into V1 and most of the gain was restored, but the overall volume was really low. Then I took out the other new spax7 from V2 and replaced it with the original groove tube 12ax7 and also with a new mullard reissue (standard gain not high). Both of those fixed the volume issue. I left the mullard in since the groove tube was way too bright.
I have a hard time believing that both of the brand new spax7's are faulty, but I guess it's possible. Even if they are, would the lowered voltage really make that much of a difference from tweed to full power? Anyone heard of this happening? Ideas?
Thanks in advance!
Problem: About a month ago I changed out most of the preamp tubes. Some were noisy and I was also testing tonage. I changed v1 + v2 with MB spax7's and v3 + v4 with mullard reissue 12ax7's - high gain (from tubedepot.com). After I did that the lead channel had very little gain when running in Tweed mode. With both drive and gain pulled out and set around 8, it had a little more gain than rythm 1 and less than r2. However, the gain was fine in full power mode. After some messing w/ it I found that the problem was from the new spax7's in v1/v2. I put the original spax7 back into V1 and most of the gain was restored, but the overall volume was really low. Then I took out the other new spax7 from V2 and replaced it with the original groove tube 12ax7 and also with a new mullard reissue (standard gain not high). Both of those fixed the volume issue. I left the mullard in since the groove tube was way too bright.
I have a hard time believing that both of the brand new spax7's are faulty, but I guess it's possible. Even if they are, would the lowered voltage really make that much of a difference from tweed to full power? Anyone heard of this happening? Ideas?
Thanks in advance!
