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@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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