Congrats!
V1 is the closest tube to the front, V2 the other.
Check the
Stock Gain Mod instructions for the OD Trimpot (T2) adjustment:
Step 10: Tweaking the OD1 Trimpot
Here is how to set the input stage gain-trim:
1) Plug your MP-1 back into your rack, make sure you have ample access to the top of the unit.
2) Locate the OD1 Trimpot you replaced in steps 6 & 7.
3) Dial-up your favorite high-gain patch.
4) Grab your main axe, plug it in, and switch to your bridge pickup.
5) Set the OD1 Level Control to 5.0 or 6.0 (or 7.0 depending on your pickups). You will have to play
around with this setting until you are happy with how the other channels sound, especially the Clean-
Tube channel. I wouldn’t let this setting get above 8.0, it may get too muddy or noisy.
6) While you are doing palm mutes and/or heavy open chords (“Pull Me Under” is a good riff to test
with BTW), have your little brother turn the trimpot dial with a little miniature screwdriver until the
OD1 Clipping LED lights up frequently on downstrokes, but doesn't stay lit all the time.