If your Drake R4A (ham radio) has blown its output transformer, a possible replacement is the Hammond 166G6B. Although nominally the same size as the original, the new transformer is slightly larger and will go above the chassis in front of the can capacitor. Connect the 120 volt winding in the plate circuit and the 6.3 volt winding to the headphone jack. If the radio now squeals loudly, reverse the plate circuit leads.
N.B. You will have your fingers in high voltage wiring. Unplug the radio before you do anything. If you are not comfortable with this work, find someone who is.
Another Note: This modification is not intended to "improve" the sound of the radio. Opinions of how the radio sounds better are as common as elbows. This mod is to save a fine radio that would otherwise go in the trash.