Tube coil questions (833A's etc)

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Robert by way of Terry Fritz <twftesla-at-qwest-dot-net>" <obiwan1186-at-sunflower-dot-com>

I've been hearing a lot of people talk about VTTC's lately and I am 
inerested in building one to get away from the conventional spark gap 
tesla coil (i've built a 4.5" one and am working on a 1.5" one), but i 
have a few questions. first, where can i get one or two 833A's and how 
much do they cost? i've seen them run for almost $100. is that really 
how much they cost or can i get them any cheaper? second, what is the 
purpose of having two coils that are coupled to the secondary? can 
anyone point me to some resources about these? thanks a lot,
Robert