I will also chime in on this, as I made up a large PC board to accommodate the entire shunt regulated power supply, the driver load, and the regulator for the driver cathode. All of those components dissipate quite a bit of heat, but when you look at putting the 6CM7 onto the PCB, you have to remember that little tube is dissipating 7-10 watts. With something like a wire wound resistor, this would be the situation of having a 25 watt resistor with a large body to throw off the heat, and you could space it off the board. With a tube socket, there are many connections to the board and very close proximity. This is a lot of heat for the board to contend with, and I generally feel that this isn't a reliable way to build an amp.
Also, I find something somewhat horrid about designing a PCB with heater traces and the signal circuit all in one. I like being able to shield the heaters, and having some short jumpers from the PCB to the tube sockets to allow the heat to go elsewhere...