MOTM

>I've long wanted to build a Master Clock box to let me run all my
>sequencers and arpeggiators from one source.

Would that be any different than choosing one of the clock sources you
already have??  If you use MIDI, SMPTE, or use a digital multitrack, that
should be the master.

>It would need to have a very stable clock (20bpm-200bpm) with various
>outputs ie. clock/2, clock/4, clock/8. It would also have negative
>and positive going triggers, gates and a few inverters.
>
>I recall that in the 70's there was a device like this called Doctor
>Click.
>
>Does anyone have schematics or ideas for building such a beast?

I have a Garfield Dr. Click.  It was made in the early 80's.  It does what
you say and more, however I usually slave it to the Sync24 or arpeggiator
clock output of my Kenton Pro4.  I don't have the schematics, but even if I
did, there would be no way you want to clone it!!  It has several massive
PCB's filled with _hundreds_ of chips.

Afaik, Blacet sells a chip that extracts MIDI beat clock, and it is not
difficult to build circuits that divide by even numbers.  I would do a web
search, and look at the application notes for CMOS 4013, 4018, 4040, 4047;
7474, and the 555 timer.  Pay attention to pulse width -- not all divider
circuits work the same way.  You should also be able to find a number of
gate and trigger circuits at the various synth sites.