Just stumbled across this on FSB. It's a tap tempo + modulation add on for PT2399 delays designed by Electric Canary. It is digital so you'll either need to buy a pre-programed chipset or burn the code onto the chips yourself. Lots of off board wiring with this, but it's probably worth if you have a favorite PT2399 delay you want to take to the next level. Check out their site for more info, schematic and the code.