[TowerTalk] Fixed capacitor source needed (150pf 5KV)

TexasRF at aol.com TexasRF at aol.com
Thu Oct 3 11:18:06 EDT 2013


Herb, an Ebay search for 150 pf capacitor shows a source in the Ukraine for 
 4 ea 150pf 6kv ceramic capacitors for $10.75. 
 
If you are into home brewing some caps, one can use copper plates and  
teflon insulators. The needed formulas are in the ARRL handbook. The design  
would start with 150 pf and adjust for the dielectric constant of teflon. Then  
the air dielectric value (approximately 150 times .68) and the dielectric  
thickness is used to determine the surface area required.
 
Normally the chassis or enclosure is used for one of the capacitor plates  
and a copper (could be aluminum) plate is used as the second capacitor 
plate. A  single screw with a suitable insulator is used to hold the thing 
together.
 
Other dielectric material can be used as well by adjusting the dielectric  
constant as needed.
 
Some really robust capacitors can be built this way but they are somewhat  
larger than conventional capacitors.
 
73,
Gerald K5GW
 
 
In a message dated 10/3/2013 7:48:12 A.M. Pacific Daylight Time,  
herbs at vitelcom.net writes:

I have a  Drake MN2700 so I can at least get the amp to work above 
1870Khz during  contests.  The tuner used some fixed flat 150pf 5KV 
capacitors to  switch in from the front selector as increased capacity is 
need to make  the tuner work.  I can't find any door knob substitutes at 
that value  in my junk box. I am thus looking for a source for these 
values but so far  have not found anything that I can use as a 
substitute. I presume I could  make some out of sections of RG-8 mini 
roller up in a coIl but before I  try this I am searching for a door knob 
source.  I have some 500pf at  5KV and three of them in series might be 
close enough but i still need the  correct values.  If any reader to this 
knows of other ATU  manufactures that use the copper teflon flat 
capacitor in their units  maybe   could order 150 pf 5KV from them.


Your help on  this would be appreciated.


Herb,  KV4FZ
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