Hi;
I'm curious as how the receiver would behave when it is used just as preamp w/out any speakers connected directly to the receiver. Would it get as hot as it does in a normal setup where it is connected to speakers? Theorically, it shouldn't right? The only heat that should dissipate from unloaded run is leakage and the processor which shouldn't be much.

You are correct. The amps and associated power supply are the biggest heat generators in a receiver.

Theimage I've noticed that my H/K 635 runs warmer during two channel listening than does the Rotel amp that is connected via the H/K's preouts for two channel listening. Over on the Rotel site I've read where the Rotel 1098 processor runs very warm.
I was wondering your very same thoughts just a couple of days ago.

The reason I asked is when I used my H/K435 purely as preamp, it seems warmer that I expected. I haven't tried to compare with running the receive by itself.

HK's seem to have higher idle currents in the power amplifiers than most receivers. This is good in the sense that it lowers distortion at low volumes, but bad in the sense that it idles hot...

In theory, you are correct. If it isn't, I would start asking the question, WHY???? The amplifiers should not be generating more heat.

One possible exception is that the amplifiers may have some sort of "internal" load so that they never see an open circuit. However, I would not expect that "internal" load to generate much heat.

Im, to illustrate the point that John B. made about power at idle, note the specs on your 435 which show 59 watts being consumed at idle(the same is true for Rick's 635). That's an awful lot of power coming in with none going out to the speakers, so it has to create significant heat.