It might take ten times the power to run a tube rig on idle as
solid state. I'm not sure of the real numbers but I'd guess 5
watts for my solid state ICOM and 50 watts for my SB-102.

Most manufactured solid-state rigs require 1-2 amps on receive - that's 12-24
watts.

I don't know what model ICOM you refer to but 5 watts at 12 volts is less than
half an amp.

The SB-102 requires 12 volts at 4.75 amps (or so) to light the heaters, 300
volts at about 100 mA B+, and some bias. Works out to 57 watts of heaters, 30
watts of B+ and maybe 3 watts of bias - say 90 watts total. Press the key and
you add 800 volts at 240 mils - about 280-290 watts total.

Remember, though, that the efficiency of the power supply has to be considered,
both in the solid-state and tube case. In the case of heater power, a
transformer is very efficent (90-95%). Unregulated DC from a typical SS suply
is almost as good - (80-90%). Regulated DC (typical series-pass-transistor SS
supply) can be much worse - down to 50% (worst case) when a big supply runs at
light load, because the pass transistor has to burn up a lot of volts.

So in the case of a tube rig that needs 90 watts from the power supply on
receive, the AC demand might be 110 watts. Compare that to an SS rig that needs
2 amps at 12 volts on receive but has a power supply with ~50% efficiency at
light load - total AC demand 90-100 watts. (This is why switching supplies are
so popular - they are very efficient).

If your primary power source is 12 volts, it's a whole different ball game
because the SS rig doesn't even need a power supply.

--

On transmit, my ICOM spins the fan and draws 20 amps at 12 volts,
240 watts. The SB-102 might take 300 watts.

Both are reasonable numbers, but note that often the "12 volts" is actually
more like 13.8.

The Elecraft K2/100 requires only 250-350 mA (depends on options) at nominal 12
volts on receive. I don't know of any full-feature rigs that draw less on rx.

73 de Jim, N2EY