I have an older model 84CS amp with volume controled input jacks on the back and direct input jacks on the front (near the 6n1p input tube).  Is it OK to hook up two inputs to this amp using both sets of inputs?  There is no switch between the two, so I would only be running one source at a time.  If I were to have a mental lapse and play both at the same time would I take the chance of frying something?  Does playing one source while leaving the other one hooked up hurt anything?  I figured I would ask first before I break something or turn my favorite amp into a smoke machine.