my jcm 800 2210 is in the shop and the guy doesn't know whats wrong ,right before it happened i had been wiring speakers into cabs ,so i thought maybe i did it ,but now i don't think so because my dmm's are giving me good readings on all 3 cabs as they should be(2 8 ohm cabs 1 16 ohm cab) . and the amp still functions ,but the symptoms are only these : the amp howls when not in use,but turned on (toggle switch in off position of guitar plugged in) ,the reverb potentiometer is not acting right ,when it is on any other position except 8 the volume is up too high even with the master on 0 ,when u turn the reverb to 8(8 is the position i always have it set to ) it quiets down . i want the pot replaced ,but the tech said he cleaned it and they might be scratchy but not in need of replacement . i'm ready to pick it up and take it elsewhere ,i need my head back ! i just spent 700 dollars on 2 jbls d120f's and 1 greenback and 1 evh speaker! he says the problem is intermittent ,somtimes the sound happens sometimes it doesn't . i'm going to tell him to check for output transformer ,faulty component in the reverb ,microphonic preamp tube . bad output or power supply . cracked solder joints . any other ideas?