The song of the week is 'Nine Pound Hammer' in the key of B.
Here are a couple of good performances of Nine Pound Hammer to listen to:
Lonesome River Band - key of B
Tony Rice - key of A
The chord progression for Nine Pound Hammer is:
In the key of B: 1=B; 4=E; 5=F#
The B chord consists of: BD#F#; the E chord: EG#B; the F# chord: F#A#C#
Breaks, Improvisation, and Scales
While the intro break for the song should follow the melody closely enough to make it clear what song is being played before the first verse is sung, Nine Pound Hammer lends itself quite well to lick-oriented improvised breaks that may deviate considerably from the melody. (See especially the second youtube link above for examples of this.) This is a good song to use as a means for practicing any licks that you may have in your repertoire that fit over a line of 1144 or a line of 1511 for the key that you are playing the song in.
On mandolin and fiddle, a good place to get started with finding suitable notes on your instrument to make use of in licks for improvising over Nine Pound Hammer in the key of B is to run through the B Major, B Major Pentatonic, and B Dorian Scales:
B Major Scale = B, C#, D#, E, F#, G#, A#, B
B Major Pentatonic Scale = B, C#, D#, F#, G#, B
B Dorian Scale = B, C#, D, E, F#, G#, A, B
On guitar, banjo, and dobro, run through the equivalent G Scales with the capo on the 4th fret to raise your key of G playing up to the key of B:
G Major Scale = G, A, B, C, D, E. F#, G
G Major Pentatonic Scale = G, A, B, D, E
G Dorian Scale = G, A, Bb, C, D, E, F, G
When playing without a capo in keys that have a lot of sharps in their key signature, I tend to try to find more spots than usual in my breaks for where I can make good use of 'blue notes': flatted 3rds and flatted 7ths (observe that these are the two notes in the dorian scale that differ from the notes in the major scale) but only to the extent these suit the song. The reason for this is that in these keys, flatted 3rds and flatted 7ths end up being notes that frequently occur in the more 'user-friendly' keys of C, G, D, and A. In the key of B, the flatted 3rd is a D note, and the flatted 7th is an A note. Unlike the 3rd and 7th scale degrees of the B major scale (i.e., D# and A#), both of these 'blue notes' (D and A when in the key of B) are part of the major scale for all the keys that I feel most comfortable playing in without a capo.
Nine Pound Hammer lends itself especially well to the use of blue notes in breaks, so even when playing it in keys that don't have a lot of sharps, I still tend to use about just as many blue notes in improvised breaks for the song. In the key of G, the flatted 3rd and flatted 7th notes are Bb and F respectively.
Closely related to the use of blue notes is the use of 7th chords. One can make good use of 7th chords in improvised breaks during a measure of the 1 chord that is followed by the 4 chord, and also during a measure of the 4 chord that is followed by the 1 chord. 7th chords are created by flatting the 7th major scale degree of the chord being played and adding that note to the chord. E.g., the 7th scale degree of the B major scale is an A# note. Flatting this note (i.e., lowering it by a half step) gives the A note. Adding the A note to a B chord results in an B7 chord. The 7th scale degree of the E major scale is a D# note. Lower this note by a half step and you have a D note. Add the D note to an E chord and this creates an E7 chord. Adding an F note to a G chord makes it a G7, adding a Bb note to a C chord makes it a C7, etc.
Practicing with a Capo
For guitar, dobro, and especially banjo players who have much less experience playing in B than in G and A: I suggest making it a point to spend some practice time playing with the capo on the 4th fret (with the 5th string, on banjo, spiked/capoed at the 9th fret), for although the fingerings for playing in B will be the same as those for playing in G, the instrument will feel different to play: the frets will be closer together, and the strings will feel a bit tighter; and on banjo, it can get a bit confusing to see the 5th (short) string being located directly above one's left hand when one is playing in first position if one is not used to this.