Big Pimpin' with the RCA Synthesizer Mk II...
Metasonix ain't the only game in town for tube synths. If you want to go vintage, you could do worse than the RCA Synthesizer Mk. 2, pictured above. (Or part of it pictured above, anyway...) Here is a recording of this beast in action, courtesy of Obsolete.com, who have a pretty complete article about this synth, installed in 1958.
"Yes, but Chris, I'd swear that photo looks relatively current," you say to me. "Those aren't chairs from the 50s!" Good eye. The above picture, taken from this site, (one of a couple dozen, as you'll no doubt find out) is of the synth as it currently stands, still in its original home at the Computer Music Center at Columbia University. As far as I can tell, it is still in operating condition.
Take special note in the Obsolete.com article about how it is "programmed," via punched paper rolls. That could really take the fun out of making music, I think.