rene,
yun 5751 pang-giyera sa afghanistan, irag, kuwait, lebanon....yung 12ax7 pang peaceful countries.
kidding aside, the 5751 is a milspec of 12ax7 family with a lower gain as cited by my friend Superman. in some set-up, the 5751 excels than the 12ax7. in short, find out for yourself in your system.
btw, thanks for the spy tips...alam mo na yun.
regards!