[Amps] Using switch mode power supply for heater power

[Dr. David Kirkby]

I'm looking at building a 4CX1000A amp, which I want to make as small/light as 
practical. Using an SMPS for the heater would go some way to this, whilst 
offering regulation, since my own supply varies by more than +/-5% and a 
generator would vary even more.

The 4CX1000A needs 6.0 V at 9 A, but of course when cold it will be a very low 
resistance. I thought of using a 7.5 V 13.5 A switch-mode supply, with a 0.17 
Ohm series resistor to drop 1.5 V. But I'm concerned the heater will never get 
hot, as the cold resistance of the tube will draw too much current, causing the 
SMPS to shut down.

If I bought one rated 12 V at 18 A or more, then dropping 6 V across a 0.67 Ohm 
series resistor would mean the current would never exceed 18 A, even if the 
heater is a dead short when cold. But that's a lot of wasted power, and an 
over-specified (i.e. expensive, heavy) power supply.

Another option might be a NTC inrush current limiter. I've not looked at what's 
available, but I do know device exist for this sort of task.

Does anyone have any ideas on the best way to use an SMPS for a heater supply?
-- 
A: Because it messes up the order in which people normally read text.
Q: Why is top-posting such a bad thing?
A: Top-posting.
Q: What is the most annoying thing in e-mail?