Rock-ola 434 HUM adjustment and problem?????
 

Hi guys , i have a Rock-ola Concerto with tubes amplifier , anyone
knows what the HUM adjustement is suppose to do ???? it does not seem
to do any differences when i turn it !!!!!

and Is it normal that when i select a new song ,while playing , i hear
hum from the selector motor !!!! any cure ?????

Thanks