Charlie:

I don't think the mods are being made for the ST-70 anymore. The original circuit was pretty simple, and had some comprimises, but the basic guts like the transformers were excellent.

Yes, you are quite correct - you shouldn't buy a tube amp for 'bang for the buck"! You have to be very careful about what they are connected to. Generally, speakers that need a lot of power, and / or have complex crossover networks are not a good candidate. On the other hand, tube amps shine with horn speakers, in fact they are almost mandatory for high efficiency horns that have corssovers much below 2Khz. It's all a matter of application. The amp that drives my tweeter horns (1,200Hz and above) has only 5 watts, but with sensitivities of 106db for _one_ watt, I am asking for much less than one watt, even at ear bleed levels.