As an aside, the actual bulb used is a 211-2, and there are two of 'em in parallel. The 211-2 bulb is designed for 1A at 12V (12 ohms) but cold resistance is only about 2 or 3 ohms, so the pair is about an ohm and a half. When used on the input of the crossover, there is no noticeable impact until high current makes the filament glow, increasing resistance and limiting current. It acts like a compressor and protects the tweeter, but the compression effect is very natural sounding, you can hardly even tell. And it doesn't happen until the amplifier is generating about 300 watts.