Gain problem: in amp or guitar?

Has the gear been played in the same place all times? The room makes a huge difference. Also, ive noticed that on some days the gear just sounds off to me. Ive been told by people that when it sounds off one day, don't make a lot of changes... it could just be your ears... and for me anyways that has proven correct. Not saying that's your issue, but just something to think about.

It's been in my room for the most part. The weird thing is is that it is a considerable gain difference. Ok... Just played it and now it's back to normal... My friend said he had the same problem on his Hughes and kettner tumbemeister 18 but jiggled his bridge pickup around and it solved the problem. I just wouldn't have thought that a gain problem would originate in the pickups.

I will start out with my gear
Schecter Damian solo elite
Schecter hellraiser extreme c1 fr
Peavey raptor plus exp
Randall RG75 G3plus

Damian has emg81/85 and hellraiser has emg81/89

I have no idea what the peavey has since I haven't played that one in years.
To the problem: I bought the amp used about 3 months ago and sounded great. I picked it up today and there was almost no gain when I played the Damian. I switched to the hellraiser thinking it was a tube problem but it sounded fine. It sounded fine with the peavey as well. So I guess it cannot be a tube problem. Three days ago my Damian sounded as full as ever. Now it sounds clean with barely any gain, with the gain knob at max and on the gain channel. So the problem should be coming from the guitar, but I never thought that gain started in the guitar. I believe it starts and ends in the tubes. All in all I am asking where is the problem and how should I go about fixing it? Feel free to ask questions for more clarification

Change the battery in the Damien. You might want to go ahead and swap out the one in the Hellraiser also. Your guitars use active pickups and need a power source.