[morzh]

One thing is, try not to exceed 110-115V while you are fixing it. I found out some radios at about 115V and up will produce a loud hum they are not producing at below 115V. I spent 3 hours trying to rewire grounds in my 38-15 to get rid of the noise only to eventually realize it does not even show if I am under 115V.
One less variable. Once you fix it you may try unadulterated Mains voltage to see if it behaves well.