I have asked them about my 74 Harmony H906. They don't have any thing about it, on it, or anything having to do with that bass. She's beast of a bass. I have the push pull pots, the original spdt switches, a blend pot, I just bought two dpdt slide switches. Both humbuckers are chrome with 4 pole screws, and a red, white, and a bare wire from both pickups. I'm teaching myself how to rewire guitar and bass. So, I'm just experimenting with what I have here. I've already had the neck humbucker from a Les Paul installed with volume pots both with the treble bleed circuit.