not the secondary transistor-opamps-coils mounted on the PCB.
In the top lid there are also venting slots and because the PCB's are mounted on a quite low position in the housing there is a lot of air around the parts and this air comes out on top. The heatsink is mounted on the low side of the cabinet so there is still some space for the hot air to go out on top.
I measured the heat everywhere and the biggest heat comes from the heatsink/Tbone, not the 12Volt transistors and output coil. Yes they feel hot but have no heatsink. These are just minor heat generators. The output Fets have a idle current of about 60ma x 120 Volts which is about 7.2Watts to burn for each amp. Maybe more. Bruno will know.
If you feel the amps. temperature after playing for 8 hours you will feel that the heatsink has the biggest chunk of heat from the output fets. The heatsink will reach 55C.
I had them vertical in my first try of the UCD's in a housing used for my Crescendo's. But this was not the best solution. The housing was bigger and had a lower volt toroid(2x35V) so it did not get that hot.
[IMGDEAD]http://www.xs4all.nl/~grotel/Photo's/UCD%20vert2.JPG[/IMGDEAD]