24V to 0.6V means a transformer turns ratio of 24/0.6 = 40 to 1. But the impedance goes according to the turns ratio squared, so an impedance ratio of 40x40 = 1600 to 1.

With a 4 ohms speaker load that gives a primary impedance of 1600 x 4 = 6400 ohms

Or a 16 ohm load gives 1600 x 16 = 25600 ohms.

Don’t know what the output tube(s) are, but the 4 ohm version looks more reasonable.

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