The standard grips this chord is usually shown with.
F#6 is F#, A#, C# and D#, a major sixth. The shape this page opens on is written 2x132x, lowest string first.
Note by note. F# is the root, A# is the major third, C# is the fifth and D# is the sixth.

Also written F#maj6, F#M6 or F# major 6. The same chord either way; which spelling you meet depends on who wrote the chart.
There are 10 common shapes for F#6 on the guitar, and 28 derived voicings in 3 families.
One note away. Change a single note of F#6 and you have F# (with one note taken away), F#maj7 (with one note moved), F#m6 (with one note moved), F#add9 (with one note moved), F#69 (with one note added) or F#7 (with one note moved).
In which keys. Every note of F#6 belongs to C# major (the IV), Eb minor (the ♭III), F# major (the I), Ab minor (the ♭VII), Bb minor (the ♭VI) and B major (the V).
The common shapes, written lowest string first: 2x132x, 2x4342, 24x342, xx4646, x9887x, x-9-11-11-11-11, x-13-11-11-11-11, 14-13-13-11-11-11, 11-13-11-11-14-11, 14-x-13-15-14-x.
Under the hand. None of the shapes for F#6 uses an open string, so every one of them is movable; the lowest sits at the 1st fret. 4 of the 10 need a barre. Together they cover the neck from the 1st fret to the 15th.
Shell. Root, third and seventh: the guide tones fix the quality, so the fifth is dropped. That is what leaves a string free, so pick a tension to put on top. F#6 has 211xxx, x988xx, 14-13-13-x-x-x, 2x13xx, x-9-x-8-11-x, 14-x-13-15-x-x.
Drop 2. A close-position chord with the second voice from the top lowered an octave. Sits on four adjacent strings. F#6 has xx1322, x4434x, xx4646, 6646xx, x6867x, xx8879, 9988xx, x-x-11-11-11-11.
Drop 3. The third voice from the top lowered an octave. The dropped voice becomes the bass, which is why a string is skipped. F#6 has 2x132x, x4x342, 6x464x, x6x676, 9x887x, x-9-x-8-11-9, x-13-x-11-14-11, 11-x-11-11-11-x.
Tensions. A shell of F#6, root, third and seventh, leaves a string free, and the tones that belong over it are the 9 (G#) and the #11 (B#).
What kind of chord this is. F#6 is a major chord — root, major third, fifth. major chords on every root, and what they are for.
The common shapes and the derived voicings come from different places, and both are explained in where the chords and the theory come from.
Shows each chord the way this style would voice it, and marks which of its alternatives belong to the idiom.