The Leslie 16 is the functional equivalent of the Fender Vibratone. Leslie also built a Leslie 18. The Vibratone and the Leslie 16 were essentially identical except for cosmetics; they had 10 inch speakers. The Leslie 18 had a 12 inch speaker.
This is a Leslie 16, and I love it. There has been a lot of debate about pseudo replacements like phasers, chorus's, Univibes, and other kinds of Leslie simulators, but let me tell you, there ain't nuthin like the real thing.
It has two speeds, with a footswitch that chooses either fast, slow, or off. The speaker remains on at all selections. I wish there was a "medium" selection because sometimes the "fast" is too fast and the "slow" is too slow.
In the Vibratone, there was a crossover built into the cable assembly. It sent the mids to the Leslie, and the lows and highs to the normal speaker. A switching system would blend in the Leslie with main amp and speaker cab. Mine doesn't work this way, I drive it with a separate amp. The crossover has been eliminated and the full signal goes on through, and I prefer it that way.
Compared to a regular amp, this thing is a lot lower in volume simply because there is no direct radiation of sound, (it comes through ports on the side and top) and there is only one speaker. I drive it my with my 50 watt Blackface Fender Bassman, and there is a significant difference in volume to my main rig. I use a Morley A/B/Y box to to switch them together or A/B. They sound killer when used together.
I have replaced the stock Utah speaker with a Ceramic California 10 from Ted Weber in this cab; it takes more power, is more efficent and brighter, and is an overall improvement to the sound.
Yes it is damn heavy, probably about 60 or 70 pounds, but once again I say it sounds so cool.
And no, I didn't buy this thing because I wanted to sound like SRV.
Click here to download the original Vibratone Manual.
Here is a very good site with lots of information on the Vibratone/Leslie 16-18.