Oldest 600b have ever seen

Altec 600B DIA-Cone 12" Speaker #2 | eBay

Hollywoods.Blow up the pic.

Guy has two listed.Reconed.

I'm not familiar with the 600B........ are they supposed to have aluminum dust caps?

Yup. Extended range speaker excellent voice range.

For lack of better description, ancestor of 417 guitar speaker.