I am thinking about buying a second hand AlienBee 800. I currently have a pair of Yongnuo YN-622C Wireless TTL Flash Triggers for Canon. Would they be compatible with the AlienBee?
You can, using the sync port on the Yongnuo trigger. However, AlienBees use a 3.5mm mono sync, so you'll need a cord that can connect the two up. Fortunately, they exist and Paul Buff sells them. You can probably also find smaller cables, but you may want to consider the long ones anyways as they may let you do some funky strobe positioning, behind things that might block the radio signal.
As a note, if the AB800 you get has the complete shipping kit, it will include this cable. It's used, though, so may have long since been lost. You never know.
I've discovered that all six of my YN-622C work only intermittently with either of two Alien Bee 800 units, but work fairly reliably with an AB-1600 and 100% reliably with Flashpoint heads. Upon investigation, I've learned that the Flashpoint heads supply 6.0 volts on the trigger pin. The AB-1600 heads supplied 4.72 volts but the AB-800 heads each only had 4.25 volts. There's a direct relationship between the reliability and the DC voltage on the trigger pins. I tried to contact a technician at Paul C. Buff, but the secretary diverted my call and dismissed my concerns and observations as irrelevant to the Paul Buff company. Because of my experience with the Paul Buff company and their lack of interest in researching the compatibilities, I can not recommend using the YN-622C remotes with AB equipment. That seems a shame, as the YN-622C triggers are an excellent product.
They're compatible for given values of compatible. :) They work as manual radio triggers, if you get a PC-to-3.5mm sync cable to connect one unit as a receiver to the AlienBee 800. However, the "supersync" (aka hypersync, tail sync) feature, which allows for faster-than sync-speed shutter speeds, does not work with the AB800. The YN-566C-TX dedicated transmitter unit has the ability to adjust the timing, but so far there are no field reports of successful use of supersync with any of the Paul Buff lights and the 622s at this time.
If you want YN-622C features with a studio light, Yongnuo has announced the YN-300W, which is essentially a Canon TTL studio strobe. But it has no HSS capability, and is considerably more expensive than an AlienBee.