i have had a second hand Laney RBH700 Bass amp for about a year now. recently, i've been playing and then the volume will just drop. go really quiet. then, a few seconds later it will return to normal.

one of the wires may be lose, used to happen with my first amp, because the connection was like ever so slightly touching sometimes it would get through and sometimes it wouldn't.

If it's open back then just push all the wires in make sure it's all connected.. If that doesn't help or it's closed-back and you can't be bothered opening it up then get a pro to look at it