I just picked this up on eBay for $17.00 - the paperwork seems to indicate this is a 1969 unit. The transducer was barely working, so I replaced it with a Radio Shack piezo unit for $1.50. This piezo speaker is now used as a microphone, and it works perfectly. No battery or power is required. Just plug it into the strobe and you are all set. I purchased a Wein sound trigger in the late '70's, but sold it for some dumb reason.

One caveat though, the cord that is labeled "To Strobe" uses a regular zip cord (all original)with the two prong plug. DO NOT plug it into a wall outlet as I almost did in my haste. It is not my normal modus operandi, but for some reason I read the instructions page first before acting. Just why they didn't use something failsafe is beyond me. I believe it is supposed to have a center prong.