I have a few plotters here and a bunch of pens. My pens are probable dried up too, but I recall a friend of mine telling me a long time ago here was something you could inject into the pen that made them useable. Unfortunately, I don't remember what is was. Paul On Sun, Jun 29, 2014 at 7:49 PM, Philip Pemberton <classiccmp at philpem.me.uk> wrote:

IRIC the 7470 is the 2 pen model with a pen holder at easch end of the carriage rail. The carrage moves off-limits to pick up or put down a pen.. II also seem to rememebr that soem pens are too long to fit in the unit, but all 'standard' HP ones work. As an aside, there are at least 3 versions of the 7470. The common ones are RS232 or HPIB. The 'Opt 003' is much desired in some circles. It has an HPIL interface, and was used wit hthe HP41 and HP75 handhelds. There is even a pltoter ROM module for the HP41 (which contains programs to drvei said plutter [1]) and a 'graphics solutions book' (programs on magnetic cards to draw bar chrats, pie charts, etc) for the HP75. [1] Acutally, said OM wil lwork with just about any HPIB plotter using HPGL commans if linekd up via an HP82169 interface. It does not work with RS232 plotters (linked via an HP82164). I wonder what the solvent in the original ink was. I asusme that jsut thew solvent has evaporated and that the pigments, etc, are still there. If you could find a suitable solvent you could probably get the old pens going again. -tony