Barry Lennox wrote:
A year or so back, there was a tip (in FWW) by Jimmy Carter on
sharpening jointer blades in-situ. I did not pay much attention at the
time, as I did not own a jointer, I have now acquired an old one with
3 sets of blades, 1 set is OK, just, but the other 2 are worse for
wear.

What was his technique?

Barry Lennox

There is a hand held hone that one can use to touch up jointer blades.
You can buy them from all the usual places, e.g. HD, LV, etc. If by
"worse for wear" you mean that they have nicks and flat spots, take/send
them to a professional sharpening service.
mahalo,
jo4hn