Hello, I got my RM-1 from Elderly Music this past summer. It was one of the first ones National made (has a low number engraved on the back of the headstock). Though I loved the sound, it had a few issues - very high action, and, more unusual, certain pitches that warble - particularly the F# 2nd fret first string. That note would warble no matter what string or fret I played it on - so I assumed the cone needed adjustment. Well, I sent it to one of the local guys here in Kansas City that just about everybody sends their instruments to for a setup, and he really butchered the job. When I got it back I couldn't tell any improvement in the action and the warble was still a problem. So I decided I'd do it myself. I removed all the strings, then I removed the tailpiece so that i could remove the cone cover. When I did that I discovered one side of the biscuit was lightly gouged by the slots - he didn't take the cover off when he tried to lower the action, so he just sort of defaced one side of the biscuit by, I'm assuming, running a file under the cover and trying to lower the slots without proper access to the biscuit. I marked the depth I wanted on the biscuit with some masking tape then using a saw blade I deepened the slots until they touched the masking tape. Lifting the cone was nice because I could admire the fine workmanship that went into this instrument. The inside is chambered. I assume this chambering is why the RM-1 sounds more like a very loud mandolin then a standard resonator instrument. I was HOPING that by turning the cone I would eliminate the warbling, but the cone was seated tight as it was, so there was nothing I could do. I reassembled everything and restrung it with lighter gauge strings and the warble, though still noticeable, was much less. The action, however, was leagues better. Since then the warble has almost disappeared. I don't know what causes it, occasionally it'll come back slightly but not loud and annoying like it was before. I would encourage anybody who has one of these to not be afraid to take a screwdriver to it. I spent about an hour total and came out with a MUCH better instrument.
Thanks for all the detail. Since mine arrived (from the factory) very well set up, I haven't had the need or courage to open it up. I will add that, based on advice, I strung it with JazzMando strings and bought a Blue Chip TPR60 pick. I know there is a mixture of opinion about these things, but I'm convinced both contributed to the quality of the sound I'm getting. They're well worth the few extra bucks.
