My 1973 Silverface Twin Reverb has excessive hiss, especially with the Master Volume high. On the Normal channel, Normal Volume at 10/Master at 2 is clean with only a little hiss, but Normal Volume at 3/Master at 10 has very distracting hiss while the guitar signal remains clean. On the Vibrato channel, Vibrato Volume at 10/Master at 2 produces rattly, distorted, unstable sounding guitar audio that seems like the signal is about to give out. It sounds distorted as if the amp was breaking up which if I’m not mistaken it’s not supposed to since it’s a twin? This happens through both Vibrato inputs and doesn’t matter if the bright switch is on or off. With Vibrato Volume 3/Master 10, the guitar signal is clean but the background hiss is very prominent.