When were the best tube amps made?

@alexberger  Those look like tube names, not amps. :)

Erik, I didn't find your OP trolly.  But the SP10 is an 80s AR design and it is difficult to beat.  But when Krell entered the market around that time with the KSA50, it had that era's valve amps beat.  I still have mine and it's still very good.

Why should I care?

1987

the best tube amps are being made now.

modern power tubes are in some important ways “better”, i.e. kt-120, Kt-150 and Kt-170 have greater plate dissipation.  So amps using those tubes can be designed which exceed past efforts, in a more compact form factor.

modern biasing controls have advanced, yielding better sound see, e.g., VAC.

even transformers have advanced; amps can be designed are quieter toroids with wider bandwidth.  Capacitors and other parts are improved. 

I loved my Mesa Baron, but 12 power tubes was too much to deal with.  Keeping an old tube amp going is like having an old sports car - more ongoing maintenance is required than a modern design.  To send it back to the factory cost over $500, round trip. 

the build quality of my Rogers integrated is Nasa-satellite level, way better than anything from ”back in the day”