First rule of shielding is to protect the signal “ground” also. You need to replace your simple unbalanced fake-“shielded” cable from your tonearm to the phono stage with cables that have fully shielded twisted pairs, one cable per channel, such as Belden 1696A. The shield drain wire connects to the tonearm ground at the turntable side, and to the phono stage chassis ground at the other side. Make sure the tonearm ground is isolated from the turntable chassis. All interconnects should be made in this way for line level signals, except the shield drain wire only connects to chassis ground at one end - with the preamp usually being the most suitable end.
Trying to reduce noise while listening to tube phono
Let me start by staying that I'm in love with how my system sounds right now. Hagerman Trumpet and Decca London Super Gold (paratrace stylus) is a ridiculously good combo. The only "but" is that if I raise the level to 3 o'clock on the preamp (Herron) I start to get tube hiss... or some hiss from somewhere. It used to be worse but then I got all new very low noise tubes and it improved a ton but I want to see if I reduce it some more. I'm wondering if the issue is the amount of gain on my preamp? Should I try another preamp with more gain and see if that solves the problem? On other inputs there's no hiss even at full volume so there's nothing technically wrong with preamp.