* I live in switzerland, and our power supply system is 240 volt. do the amps work with that volt value?

the 50 watt have a voltage selector, even if no they can set the cable to the right tap to the pt(power transformer) wich fit your country voltage. but there a switch with this model so it'S easier.

* I will buy the head-chassis locally - but to do so, I need to know the exact dimensions of the amp-chassis, where exactly the holes are, etc.
is there anywhere a layout of that?

you can email nik he will  give you the dimension if needed, trough these should be the same dimension as the original, but i would email for make sure. (when i ordered i ordered the amp+2x12cab)

* which tubes are suggested? are the ones that ceriatone implements in the "complete amps" (already wired) good? or is it suggested to buy them by myself?
I was wondering because they only cost $ 50 (the ones that are included). anyway, if it's suggested to buy them by myself, which models should I choose? I know that some amp parts needs to be adjusted in order to implement new tubes - I can't do that, so it'd be great if I just could plug 'em in and it's done;)

for the tube he set in, i had a jtm45, so it is kt-66 instead of el34, but this where good quiality tube. i had jj/tesla 12ax7 for the preamp, and the shuguangs kt-66 for power. you can ask him on email what he set in for the el34. as for wich one to choose, that go with the taste. but the tube he set in are good.. well atleast it where on mine

* I own a thd hotplate power soak, 16 ohm. are there any (significant) differences between the master-volume modification and such a power soak? or if I have a power soak I don't need the ppmv (or how's it called) modification anyway?

someone else here can answer better thant i for this, i never used one of these ppimv(post phase inverter master volume)

* I own a iso-booth with built-in speaker, 16 ohm. is the plexi50 switchable (4 / 8 / 16 ohm)?

from the layout and pict it show a impedance selector, same for the voltage selector, there is one. HERE

i don't know too much with all this stuff, my english isnt too good am sorry for this.
i just hope this help .

I just received a Plexi 1987 lead amp from Nik, with the PPIMV.

I would say that the PPIMV on it's own is not enough to get good tone at home volumes. However, with -8dB on a hotplate as well, plus the PPIMV, all is good for excellent home volume tone, IMO.

Great amps BTW, although the head shell that the amp came in was rather flimsy to be honest. Although I can't complain. It was very cheap.

Oh, my amp came loaded with JJ's from Nik. The power tubes were the E34L's