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Registered Member #1837
Joined: Tue Dec 02 2008, 02:20PM
Location: NYC
Posts: 65
How funny, I'm building the same exact coil and was wondering the same thing. I found some doorknob caps on ebay that can get me close but I'm not sure what tolerance the coil will allow. FWIW i found all resistors on Mouser if you're still looking. Let me know what you find out. Do you have a good source for tubes? I can't find anyone who sells them with the ceramic terminals.
Registered Member #540
Joined: Mon Feb 19 2007, 07:49PM
Location: MIT
Posts: 969
C3 is just a RF bypass cap. To RF, it appears to have a low impedance but to DC (or low freq AC) it appears to have a high impedance. C1 is the tank cap that needs to be rated for a high current and along with L1 it determines the resonant freq of the tank portion. I don't know much about C2 besides it holding the tube's grid negative for the rest of the RF cycle after the tank being pinged.
Registered Member #1845
Joined: Fri Dec 05 2008, 05:38AM
Location: California
Posts: 211
Hello Everyone. I actually bought the caps yesterday. I bought 18 .0002uf caps. I will put 9 in parallel for C2 (9 in parallel provides .0018uf, or 1.8nf), and the other 9 in parallel for C3 ( gives .0018uf or 1.8nf) Then I bought a 940pf 30Kv Cap for C1.
FWIW i found all resistors on Mouser if you're still looking. Let me know what you find out. Do you have a good source for tubes? I can't find anyone who sells them with the ceramic terminals.
I got the resistors from Mouser too. I bought the tubes from the RF parts website. I got a matched pair of the 811A. I bought the 6.3V transformer from Mouser also. So I actually ordered everything I will need yesterday. I had a couple MOT's left over from a resonant mot bank I made, but it got boring and I figured I might as well put the mots to use for something else, so thats what started this VTTC project.
Flying Copper: Since I'll be starting this coil as soon as the parts arrive, I'll definitely let you know how it goes. Its kind of a group project now. lol
Thanks for the info about the acceptable capacitor variance guys. I'll definitely put it to use if I build another VTTC.
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Capacitors within VTTC
