Yes, I had similar happen in 2010. I know it sucks. It was an EH KT90 in one of my Rogue Apollo monoblocks. They're no lightweights at six KT88/90/120 per side, but still nothing like your 750! Anyways, yeah a few seconds of fireworks and then a pillar of smoke. No big BANG, fortunately.
The tube (presumably it shorted out) and its resistor (a big blue metal oxide one) were toast. It also singled the board under the resistor, stripping the green mask off and exposing 1cm of bright copper trace. It would've been OK to just replace the resistor and tube, but since the amp was only a few months old at that point, I sent it in and got the full audio board replaced. It didn't put me off tubes - sh*t happens. I swapped to KT120 shortly after this incident. 13 years later and I've never had another tube incident.