ringing bell in speaker

[Old1625]

I have one of those 810s. Cute little set. Some day I may pull the thing out and fiddle with it...

Before doing anything else you might want to try replacing the audio output tube. Can't remember for sure about the 810, but in many of those compact sets the B+ to feed all the Rf and IF stages was taken off the cathode of the audio output tube. If the output tube gets weak then that B+ feed drops below what will make those stages operate well. Poor contrast to nothing but a raster will result. Microphonics can also be another symptom of a tired output tube.