Recto Orange channel problem???

[plapnab]

Question: Was gigging a couple days ago and was playing on the orange channel vintage of my dual rec when I noticed the sound starting to fade out a bit. At the time I though it was just the battery in my guitar going dead. I designate the orange channel to one specific guitar and was on the last song of it when this started to happen...the rest of the night was spent on my other guitar on the red channel modern and green clean which it where it's at 80% of the time...no problems there what so ever. Anyhow, when I went to check on it today turns out the battery is was fine. Checked the amp as well and everything seemed ok. Could I have a preamp tube starting to go bad. Usually, with orange and red channel issues aren't they both run on V3? No problems with red so it seems???