Two ways to do it. The cheap way is to change the tube to a good NOS tube. I've tested over 15 different NOS tubes in there, so far my favorite is the Mullard Master Series M10 6DJ8. But it is hard to find. I was lucky to find one. The Amperex 6DJ8 with orange label and a globe logo, white label 7308 are also on top of my list. (This is based on the LS2B MkII I have) The Amperex 6DJ8 orange label is the cheapest.
The other alternative is to upgrade to the LS2B Mk II. I would presume that this will cost over US $1,000. I would not recommend going this route. You can probably sell your LS2B and get an used LS2B Mk II for much cheaper.
The other alternative is to upgrade to the LS2B Mk II. I would presume that this will cost over US $1,000. I would not recommend going this route. You can probably sell your LS2B and get an used LS2B Mk II for much cheaper.