[Musaeum]

The mains filter is back, but that did not change the on-station-hum. Some people call it tuning-hum or modulation-hum.

With a scope I could see the audio signal was actually overlayed by a 120Hz rectangle. Probing various stages of the set suggests its already present at the output (anode) of the IF amplifier 6K7G. Channel 1 in the first pic is connected to the junction of components 20 (51k), 21 (490k) and 24 (10nF),  prior to the volume control. Channel 2 is connected to the anode of 6K7G. That weakened the signal somewhat, but it shows how the rectangle is AM-modulated on the signal.

The two other pics show probing further upstream with channel 2 on the anode of 6A8G, showing a steady signal of the oscillator. With FFT I could also see the IF, looking rather steady. Same on the connection to the grid of the IF stage. 

Could the AM-modulation happen somewhere in the 6K7G? I often read about shorts between heater and cathode. Adding capacitance to the AGC (3) and supply (14) did not change anything.

BTW, I have no reception at all on short-wave. The oscillator is running, but with much less amplitude than on "broadcast". Any ideas? When I first applied power I remember having reception of many stations, although they seemed to broadcast only noise or maybe digital stuff. Since then I twiggled this and that, cleaned the upper side...

cheers
Martin