The symptoms and the fact that the hum is 50hz and the local power seems to be 50HZ says your power supply may have developed
problems when the TDA2822 failed and the power source is the source of the hum.
Test on battery and see if it goes away.
Test the power supply for hum while on transmit at power (CW mode). Likely if the power
supply has developed an issue hum (power line ripple) could be the source.
IF the power supply is supposed to be 12V why is it sitting at 11.8V with some noise?
Another problem can be that something in your antenna system has changes such to allow excess
RF to get into the radio circuits. A common problem is high SWR on the feed line and microphone
cable picking up RF.