[RodB]

Hi Michael and welcome to the Phorum. The output transformer is there to match the high impedance of the output tube to the low impedance of the speaker. You do this to get the best transfer of power with the least signal distortion. If the 38-4 has the same output tube then you are in luck, otherwise you'll have to make the comparison from the plate impedance specs of each tube. If they're close then you're OK with it. And this is assuming the speaker impedance is the same in either radio. The higher DC resistance of the 38-4 transformer will result in slightly lower plate voltage in the 38-2 output tube but if you temporarily connect it in the 38-2 you'll probably need to raise the volume a tad.