I fired up my M15MKI for the first time today. No tubes, just to take some voltage measurements and do some basic error checking.
It fired allright - smoke and a red glow from R23! 
After some checking I found that I had reversed the polarity of one of the filter caps... Can't believe I made such a stupid mistake! It seems like all the components are fine though. R23 still measures the correct resistance although it's a bit blackened. I'll probably replace it just in case...
Lesson learnt: check the wiring again, and again, and again, before switching the power on...
Oh well, no time for more testing tonight. Can't wait until tomorrow!