The 50k pot is only if you want the bias to be adjustable. It is not necessary. The only needed change is to swap the 120K resistor out for a 100K.
Adding a fan helps a great deal with heat (and thus reliability). You might want to check that option out in addition to the resistor change.
The resistor change will take care of your power tube red plating (that is what is happening to you), and some of the heat. The fan will take care of all of the heat.
I have lugged my DC3 head everywhere. Practice, gigs, business trips, vacations, etc. It has been extremely reliable. I haven't had to change a tube in quite a while.
FYI, replace the power tubes. They are done. Once they have red-plated for any more than 5 minutes or so, they are basically done in my experience. If they don't fail right away after fixing the bias, they will soon after. Happened on one of my sets of Mullards. Took out the screen grid resistors and the fuse.
Adding a fan helps a great deal with heat (and thus reliability). You might want to check that option out in addition to the resistor change.
The resistor change will take care of your power tube red plating (that is what is happening to you), and some of the heat. The fan will take care of all of the heat.
I have lugged my DC3 head everywhere. Practice, gigs, business trips, vacations, etc. It has been extremely reliable. I haven't had to change a tube in quite a while.
FYI, replace the power tubes. They are done. Once they have red-plated for any more than 5 minutes or so, they are basically done in my experience. If they don't fail right away after fixing the bias, they will soon after. Happened on one of my sets of Mullards. Took out the screen grid resistors and the fuse.