[morzh]

If it squeals on you tell it it is not an honorable thing to do.
And make sure it is loop and not a noose

Now on teh seriuous note, I only have the sch for 48-620, but if it is also an AC/DC set, there is a capacitor or a capacitor in series with small inductance conencting the electrical common and RF common (chassis). If this cap or inductor are bad the radio will misbehave including squealing, howling, roaring, motorboating and occasionally uttering some bad words on its own at which point you should turn it off, pull the belt from your pants, give it a good threshing and then inspect for bad parts and re-align.