The V1A gain stage is the first half of the first tube on the left (from rear view). Each of the pre-amp tubes are dual-triodes, which means that they contain two separate triodes in one tube. The V1A triode is used as the channel 2 normal channel gain stage. It amplifies the low-level signal from your guitar. The Rk/Ck values connected to the cathode determine the gain and frequency response of channel 2. The classic values for lead amps are 820ohms and 320uF on a 50w and 250 on a 100w. This value is so large already, that this doesn't make any appreciable difference.
