in my opinion these should work. i say you'll need 12 to 15 of them, 3 in a series and four or five strings in paralel. four stings should give you a 60kv rateing, four times the 15kv output. thats good. .0053uf, just about matched. or five strings, .0065uf better. i could be wrong for i've never used doorknob caps, but i have seen many systems that do out there. hope this helps, mem