Stumbled across this design by Nocenteli on FSB and thought it was cool, so here you go. Mashup of the Tremulous Lune LFO and the audio path from the Magnavibe with a toggle to switch between tremolo and vibrato mode. I ended up putting the Fine control internally as a trimmer for 2 reasons: 1) In my experience with this kind of LFO it's not all that necessary, and 2) I miscounted the number of pots in this when I started layout it out and was too far in to start over. 😂 You can always wire it off-board if you prefer. Should fit nicely in a 1590B.