Tube Problem?

[Penguin]

Hey guys,

I have been hearing some crackling noises coming from my Mark IV for a while now. I searched the forum and found out that a bad preamp tube might be the cause. If it is a bad preamp tube, how can I find out which one it is? Can the spare preamp tube that came with my Mark IV replace any preamp tube? Thanks!

 

[Boogiebabies]

Yes, the spare tube can replace all of them. If it crackles all the time, try a new tube in the V1, then the V2. If it crackles in lead mode, try V3, then V4.

 

[Penguin]

Thanks for the help, Boogiebabies. I found out that the preamp tube in the V5 position was the cause. What is the role of the Phase Inverter tube?