A B7971 based Four-Letter-Word clock, designed by Raymond Weisling. This is the "second generation" version.
This clock is famous, for a couple of reasons! The original even appeared in the June 1973 Playboy Magazine Potpourri.
Raymond Weisling sold kits for his Four-Letter-Word clock through his Zetalink.biz website (web-archive), but for a number of reasons had trouble keeping up with demand.
Raymond then disappeared, owing people money for unfulfilled orders. His FLW has therefore become a relatively rare find.
DO NOT order anything from Zetalink. You have been warned! I ordered a kit in 2005 for $132, and like many others never saw it.
The B7971 tubes are also becoming rare and expensive, so if you want to build a FLW, get the tubes together before you find a kit!
Peter Hand has an alternative design based on Telefunken ZM1350 tubes, which are flat, much cheaper, and much easier to find.
The 1973 version used a diode matrix to form letters, 10 for each tube (8 for pos 2). In 2002, a "Word Bank" is stored in memory.
View of the V2 PCB design
Front views of the finished clock
Video of the finished clock