First, you don't need a matched quad of tubes for the Stereo 70. What you need is two matched pairs, as bias is adjusted by the pair. This usually makes it a bit easier.
In my opinion, the Simens are not particularly good sounding tubes, and for much less money you should be able to get very well matched pairs of tubes by JJ Tesla, SED, Electro Harmonics, etc.
In my opinion, the Simens are not particularly good sounding tubes, and for much less money you should be able to get very well matched pairs of tubes by JJ Tesla, SED, Electro Harmonics, etc.