I have searched the web and forums and it appears that this is a common problem. (I google the hell out of everything I barely think anymore) I have an F-50 that has the constant snap crackle and pop problem. This occurs with the guitar plugged in or the cable disconnected from the amp. I also tried it with the speakers disconnected and headphones plugged in. So nothing connected, not using the speakers in the cabinet, I have narrowed the problem down to the amp itself. I replaced all the tubes; that is four preamp and two power tubes with: preamp 12AX7 from Groovetube and two 6l6's from groovetube. These were recommended by my local music shop who is a mesa dealer so I'm hoping that their recommendation was correct. I bought this amp second hand fairly inexpensively so I looked at it as getting a tune up for a used car. Even after the all around tube replacement I still get the crackle noise when the amp is off standby. Any forum I search says its the preamp tube and if it isnt that there is no resolution. I would like to start this thread to find what could possibly be doing this. If anyone has any recommendations I would appreciate it. This would be my first post for amp problems so if I didnt supply any required information just let me know and I'll have it for you. My plan is tonight I was going to spray some PB blaster on the old tubes and plug them in and remove them to clean out any corrosion. Do you think PB blaster is okay for these components? Thanks to whoever is listening!