Just a few comments. I listened to a variety of music concentrating on the bass region (rather than for overall pleasure) with the choke in connected to either position (20-15 or 15-13) attached to leads 8†or so away from the base. I’m fairly certain that I would not be able to tell the difference between the two configurations (CRCLC or CLCRC) most of the time and certainly not on all pieces of music. There were a few times I felt that on a few songs, 15-13 position may have been slightly better. But once something like that gets in your mind, its awfully hard to be sure it doesn’t influence later listening sessions.
My mentioning of expecting 20-15 replacement to be better was based only on ripple reduction in PSUD2 calculations. The magnitude of the ripple current might not have anything to do with what I thought I heard in listening sessions. I certainly do not know enough about other affects that may or may not come into play.
The 20-15 resistor is a lot easier to remove without cutting leads than the 15-13 resistor. If there is a positional difference, I would hate to live off it. I would even go one step further and say that I am not certain I could tell the difference between a choke/resistor versus two resistors in a Speedball Crack – of course my ears are somewhat old. Perhaps an audible difference would be easier to discern without the Speedball?
Regarding physical placement, drilling holes behind the transformer gives one a lot more leeway. Crossing the transformer front to back as I did requires a little more careful drilling to miss the transformer plates while leaving room for the screw head (#4-40 is the way to go, a #6-32 is pushing it).
Having removed both resistors, placing the choke at 15-13 was going to be less of a hassle than working the resistor back into that position. This may have had more influence on my decision than theory or listening.
Did the plate help? I did not feel like there was a difference with or without the plate after the permanent installation of the choke in the circuit – just did one quick listening trial. But I wasn’t going to waste my $1.60 investment and left it in. If others decide to add a plate, be aware that after cutting to shape the edges are quite sharp. I decided to put a bead of epoxy around the edges to protect wire insulation and would recommend doing something similar.
I would not worry to much on which resistor you replace or where you locate the choke.
