Predecessor to the mitey VH140c. Notorious for dirty Jack's causing the volume cut you described. Open up and clean with contact cleaner. Usually all it takes is a patch cable in the effects loop. If still at pawn shop may be a bargain.
My stock pups tone improved by 1. Raising screws until threads show and 2. Replacing stock Gibson pots and wiring with quality 500k pots. If you need brighter tone than that, Gibson 57 Classic would be good stary.