[morzh]

Today decided to look for that bad connection. Took me about 2 minutes to find it and 10 minutes to repair.

It happened to be the wire that goes from the antenna coil to the tuning gang. The wire is going through a hole in the chassis, right under the backelite cap #6. After some tapping and touching, I touched that wire and the effect became very pronounced. The volume increases by about 6dB or so, and the tuning shadow really narrows. Though the tuning remained intact, I guess because of the IF stage. But the sensitivity would drop.
First I thought it was bad soldering, but then something told me it was not. I lifted the #6 cap and looked at the place where it was going through the chassis.
So what it was, the wire (low voltage type) rubbed a bit against the sharp edge of that hole and was shorting to the Chassis.
I remedied it with a piece of heat-shrinkable tubing, and the problem went away.
Now the tuning eye really narrows when tuned to the local station.

I put the chassis back in the cabinet. Will let it play awhile.

PS. There is one single crack in the grillwork; I think in the summer I will ask for some advice while trying to repair it.