I've been luck enough to acquire a Woodstock power supply 82010A which looks like it should be suitable for my HP25 - Thanks Klaus.
This raises to two questions
How do I test it without connecting it to the calculator?
Assuming that it does work is it safe to rebuild the HP25 power pack with NiMH batteries or should I did out a couple of an older NiCad batteries if I intend to use this power pack to charge them?
I note the warnings about charging batteries in the calculator but it does not look like it will be possible to get them in/out of the battery pack without them working loose in operation.
Unfortunately I've only got an old fashioned moving coil multimeter, nothing as fancy as an oscilloscope!
Mike T.