For the 2000 Pageant of the Masters I built this fire box, a fairly simple piece of equipment that consists of several medium screw lamp bases inside a wooden frame with red and amber gel stapled to it. Then I built a teepee of charred sticks left over from a local wildfire around the fire box.
This is then controlled by a GAM Flicker Master. You should be able to rent a Flickermaster or similar flicker generator from your local theatrical supplier. Or if that's not in your budget, you could program your lighting console to create the flicker effect.
I have used effectively the guts from the LeMaitre "Le Flame" (essentially everything but the cauldron) to do nice campfire effects. For one show we had fire pits that were housed under trap doors in the stage. Each one got two of the silk flame devices. I had rewired the devices such that the fan and lamps could be controlled separately. You would be amazed at how nice they looked (I unfortunately don't have a photo). The waving silk creates a pretty realistic flicker, and the lamps on them output s decent amount of light. We filled in the scene with some other lighting, but it worked really well.
Hello,
Instead of a flickermaster or other expensive product, using a starter from florescent lights creates a sporadic flickering. Each one cost only a few dollars, if that much, and can be wired in series to each standard 100w or so light bulb used in the fire effect. Put gel around or over each bulb with different colors like red, orange, and yellow. I used 4 100w bulbs, each with their own starter, mounted to a board in the bottom of a trashcan as an alley fire. It threw up nice reflections and shadows on the surrounding faces and looked really good for about $20 bucks.