Yea, thats right. The book says when the amp is idle there is only DC going through the transformer so impedance is basically zero. If sound is going through the amp then you have AC impedance. So I assume DC wire resistance acts like a resistor to keep the tube from nuclear melt down. According to my wire chart #28 enamel coated copper wire is 15.41 ft per ohm. 5000 ohms of wire is 77,050. ft of wire = 924,600. inches. Wire diameter is .01264" that = 79.11 turns per inch. If the transformer has a 2" sq core 2.5" long that is about 200 turns per layer = 1600" of wire. Each winding has 200 turns but each layer is larger is diameter not sure how many total windings of wire the transformer will have. The book has some formulas for figuring all this out. The book says the hardest part is making all the wire fit on the transformer.
I don't know the ma rating of #28 wire my book does not show it.
I am just about over dosed for the day. I guess next thing to do is calculate impedance for the primary.