Here's the relply I had at alt banjo, from Peter Roehling:

Jon Freeman wrote:
>
>When was a resonator back first fitted to a banjo?

Depends on how you define "resonator". The concept was there quite
early, circa the early 1860s, but those resonators were built as an
integral part of the pot: the resonator was glued on and did not
normally come off.

Next up would come the simple disc-shaped spin-on resonators that you
see on (for instance) Fairbanks/Vega banjos starting in about 1912.
These were certainly removable resonators, but the pots had no mounting flange and the resonators had no outer wall as do the more modern ones.

The full-out flange mounted removable resonator seems to have been
introduced by Paramount in the very early 1920s, and most others since then have followed that same pattern.

Note that all three designs do exactly the same job.

> When were tone rings introduced?

Simple 1/4" round brass rings showed up in the 1880s(?), more complex
brazed rings such as the Whyte Laydie were developed in the late 1890s, and the "modern" cast style tone rings became common in the 1920s.