Ampeg V4.com

Can you tell me which tubes are where, and what they do, when I open up the head (I can't tell what the schematic is saying.) I put a few 12ax7s in it but there is a taller tube in the back right that I don't have, and there is a section separate from the 5 on the left that I have yet to replace. I kept the old tubes after putting in four 12ax7s and I haven't replaced the tall tube or the one separate on the left. I see 6cg7 on the schematic but where in the head is that and why does the tube say 6fq7 on it also? and I see 6an8, but where in the head is that? and if I replace these two un-touched tubes, will it stop having drastic volume changes, a low ceiling and compression, and will it stop making these weird buzzing noises. I don't know anything about tube heads, I just bought this because I knew it was loud and clean. I had a line 6 head but it exploded so now I'm trying to figure this shit out. Thanks