okay so i have a svt classic bass head and a 810 classic cab and for some reason the head will cut in and out at random times. i know it is not the tubes. i've tried to adjust the "bias" controls on the back of the head but they seem to still be red at all times, even when turned all the way down. i also keep all knobs at 12 o clock except for the gain which i keep around 2-3 o clock and do not use the ultra hi/lo switches. anyway, i've been connecting to the upper input jack on the back of the cab. the cab has the upper input and the two lower mono jacks so it's a pretty old cab, but i don't think the cutting in/out has anything to do with that. i've been connecting while having the head set at 4 ohms. what would be the best way to connect the head to the cab as far as getting the most power and hopefully not having it cut out on me? also, is 4 ohms even the correct setting for this head? i would appreciate any suggestions!!! thank you!