Schematic for Bogen CHA33?

[TheOrderoftheOwl]

I am looking to add a master volume to my Bogen CHA 33. I saw one on YT and the guy simply added a pre PI master volume and switched out a filter cap. Can anyone here tell me which one is the filter cap? This is my first amp project so any info would be great! Here is a diagram of the Pre PI MV i want to use..Would this work? Thanks for any tips...
http://www.pleximods.com/images/prepimv.JPG