"Doorknob" capacitors

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

Original poster: Charles Pike <ctpike-at-rcn-dot-com> 

Murata - Erie and others make different types of doorknob capacitors.
They work by using a ceramic material with a very high dielectric constant 
of ~3000 or greater compared to about 3 for typical plastics.
In addition to the voltage rating and capacitance stamped on the case they 
usually have a code like: Z5U, Y5U, N4700, etc.  This designates the type 
of ceramic used.  Z5U and Y5U typically have losses of  ~1% and will get 
very hot and fail in high frequency applications.   The  N4700 type  have 
losses of about 0.1%  and  will probably work in a Tesla 
coil.  In  addition to these there are  other ceramics made of materials 
with numbers  lower than  4700  which have lower losses and are made for 
transmitting  applications.  However  they have also have a lower dielectic 
constant and are larger for a given value.  I hope this helps.

Charlie