Someone just shipped me a 100 watt head, and one of the four 6L6 power tubes was dark when I fired it up. The other 3 all light up like normal inside. I'm assuming that means it's a dead tube. The amp sounded normal (tones seemed correct, no noise, squeals, static, or other odd sounds) when I tested it, but I'm worried I may damage the transformer by playing it. Does a dead tube in the mix change the impedance the power section wants to see from the speakers (like pulling a set of tubes would)? Anything else I should worry about? Should I play it safe and pull out the inner pair and run just the outer pair until I can get new tubes?