I ran the Sovteks in my 5150 guitar amp --5 of em'. They were the stock tubes and always sounded grainy and noisy using the clean channel with a bad "bite" at the high end when distortion was kicked in-- for lack of better descriptions. Replaced them with JJ's where one was voiced to be warmer in the clean section. They just blew the Sovteks away in both noise and overall sound. Course this is high gain guitar stuff and not hi-fi. I just gave all the Sovteks away a couple months ago.