Song name: Marriage
Key of D
D - F#M - Bm - A(or A7)
Is F#M a secondary dominant to Bm?
It is not seventh chord, but can major chords also work as dominant chords for the six chord?
Song name: Marriage
Key of D
D - F#M - Bm - A(or A7)
Is F#M a secondary dominant to Bm?
It is not seventh chord, but can major chords also work as dominant chords for the six chord?
Dominant chords can be triads, not just seventh chords. So, yes, the F#M chord here is the secondary dominant leading to Bm. The chord progression is I - V/vi - vi - V(or V7)
.
The dominant chord in a key - V - is simply a triad. It doesn't have to be a dominant seventh - although that, with the tritone, makes it 'even more dominant'.
So, similarly, secondary dominants don't need to be secondary dominant sevenths, although the same idea is present. In fact, secondary dominants don't even have to lead straight to the chord they're dominant to - Your F♯ didn't have to lead to vi (Bm), for it still to have the title secondary dominant.