After looking at Lee's build I realize how important chassis mass is to the quiet operation of this wonderful little preamp. I have also discovered that, unlike some larger tubes, these very small tubes can be easily overdamped, muddying the sound.With those thoughts in mind I am experimenting with damping the socket rather than the tube.I placed the O-rings under the sockets which I think helps( I didn't try it without them, it just seemed like a good idea at the time). But, it does ring with the O-rings in place so I thought it might be beneficial to weight the socket in someway, pulling the socket into the O-ring and hopefully quieting the tube. I did this by hanging a weight from the center pin of the socket. In addition I tightened the retainers in an attempt to reduce movement. I used 12 lb. test Fishing Leader and a 1 lb. lead weight suspended from each socket center pin. This seems to help a lot. Here's a couple pictures.I have some other things to try yet.Sorry, the bottom pic is rotated. Imagine that the weight is hanging.
Jamie