This if gunna sound so nooby but I was looking round my amp (5150) for the first time today. I can see the four 6l6gc tubes. Then theres two blocks either end, which one has the 12ax7s in? I didn't take anything apart coz I was scared I was gunna break it which I really can't afford to do.
Haha, I read the title as 'I can't find my pubes'.
They're usually in metal casings. Look in your amp again and you should see a few metal cylinders that look like the one you see on this picture.
the preamp tubes are located in a small compartment at the back, bottom right. You have to take off a panel with a screwdriver to access it.