[sdiy] Uses for CA3039?

[mike ruberto]

I have come across a small stash of CA3039 in the metal can package
and not sure what to do with them besides put them on Ebay. I had some
thoughts about using them for a wavefolder circuit, a ringmod or even
a diode ladder VCF but I wouldn't want to use them for this if they
can be used to repair old synthesizers. Are there any old synths that
use these?
If not, what would be a good synth application for them?

M. A. Ruberto