About the High E9th tuning & String breakage.
I wanted to use E9th on the front neck and A6th on the back neck.
One serious issue with the high E9th (#0.011P G# string pulling to A) on these early pedal steels was string breakage caused by the higher note strings stretching over the sharp 90º edge of the nut before the use of roller nuts in the early 60’s.
I was afraid this may cause me to have to go to a D9th with lower tension as many steelers had done in the 50’s.
Decided that I’d first try the E9th with the high G# to A pull and if that failed I’d go to a D9th or even machine the nut to accept the two sets of roller nuts I had in case nothing else worked.
The drawback of the roller nuts being I wanted to keep the steel as close to original as possible.
As luck would have it I put on an E9th set of strings and have been playing in that tuning for over two weeks now without any breakage. Why is that with the extra long 25†scale?
On closer examination of the nut I found a very smart design in that the leading edge had an almost impossible to see rounded edge a little less than a 1/16†from the 90º drop off so the strings were not leaving the nut at a sharp edge, but at a soft angle. Looking at the close up photos you can see a very tiny almost invisible space between the strings and the nut there.
The drop off is so thin a business card will not fit in, but a thin sheet of paper will go in about 1/64†inch. Not enough to notice, but enough to do the trick. Very smart thinking on Juniors part.
The other good design feature is the string guide grooves that are below the top surface and also have soft edges so that there are no sharp parts rubbing the strings as they stretch to pull the notes up a whole or half tone.
Another surprise is that the tuned strings seem to return very well to the right note (Or very close to it) after being raised or lowered.
There is one more reason for the lack of breakage. That is the tuning I am using from top down; (
F# C# G# E B G# F# E) Usually on these old steels they had the Bud Isaacs tuning (
E B G# F#....) at first without the two diatonic strings and no high G# coming off the 1st string at a steep angle from the nut to the tuner there was less chance of breakage. Adding the high G# to A pull at the 1st string came later and with it breaking strings.
With my more modern tuning the high G# is the 3rd string where the angle from the nut to the tuner is quite mild and not the extreme it would be if it were to be the 1st string. Is this all getting too detailed?
Enough of that, Next will be some information about the tunings and copedent I will want to use. But that will be after I attend to some other business today.
Thanks for your interest,
Andy

Inlaid Star Guitar 2006 by Mark Giles. SD-10 4+5 in E9th;
http://luthiersupply.com/instrument-gallery.html
2017 Mullen SD-10, G2 5&5 Polished Aluminum covering. Custom Build for me. Great Steel.
Clinesmith Joaquin Murphy style Aluminum 8 String Lap Steel Short A6th.
Magnatone Jeweltone Series Lap Steel, Circa 1950? 6 String with F#minor7th Tuning.
1956 Dewey Kendrick D-8 4&3, Restoration Project.
1973 Sho~Bud Green SD-10 4&5 PSG, Restoration Project.