The Sunpak 421 arrived today so my questions are answered. The 421 looks like a 411 and I believe it came before the 411. The differences are: the 421 does not accept a remote sensor, the 421 does not have variable power settings and perhaps most important, the 421 has no thyristor circuit. Flash duration will vary, on Auto, with subject distance but the recycle time will be the same regardless of subject distance. In that way it's a little old fashioned but batteries have improved since it was made. When was it made? The manual which came with the flash has a copyright date of 1978. I was still in college then and the flash I used was a Vivitar 292. My 421 seems to be in nice condition and I might use it with rechargeable AAs.