[R-390] R-390A power transformer hum

[Leo Reynolds]

Is it normal for a R-390A power transformer to hum audibly? Not through the speaker, though there is a little there too, but through slight chassis vibration. It is there from the instant of turning on power and changes slightly as the rectifier starts conducting and B+ flows. It is easily audible in the shack, as if it were a small AM broadcast transmitter minus the blower.

Thanks,

Leo Reynolds 
K4LDR