This should be easier than it actually is in practice. I assume it’s a Triangle shape. But I don’t know if it’s the post-processing, possible harmonic tremolo, fingerpick attack, or what that makes it difficult to nail down (the studio version).
Maybe a Triumph Silicon 100 schematic will shed some light. I’ve had some good luck using the Ring Mod algorithm for ‘tremolo’ effects. I’ll see if I can cobble together something close enough with a dropped D tuning.