Here is a MUST mod after installing the C4S, when using
the old transformer.
Paul Joppa said this should have been in the C4S instructions.
Ground B9 to T14, it's that simple, but makes a huge difference in your noise/hum
(at least it did in mine).
I took B9 to the bottom hole of T14, as the top whole is full of stuff. DO NOT do this mod if you have the new transformer.
It already has a grounded center tap on the 6.3v filament winding.