I used short pieces of coax cables at capacitors years ago. RG8 (tells you how
many years ago) will give you a capacitance of about 30 pF/foot. I don't know
how much space you have but five 1' long in parallel will give you about the
right value. You "just" have to terminate them well so you don't get flash-over
there. If I remember right we used that cable for 5kV feeders to
photomultiplier tubes.
Hans - N2JFS
-----Original Message-----
From: Charlie Cunningham <charlie-cunningham@nc.rr.com>
To: herbs <herbs@vitelcom.net>; 'TopBand List' <topband@contesting.com>;
towertalk <towertalk@contesting.com>
Sent: Thu, Oct 3, 2013 1:04 pm
Subject: Re: [TowerTalk] Topband: Fixed capacitor source needed (150pf 5KV)
Hi, Herb
I would think that 2-3 of those 500 pF caps in series would be just fine!
Have you tried just one?
Also, are those capacitors on the load side of the tuner as an aid in
matching really low impedances? If so, you can almost certainly use
something with less than 5KV working voltage, even at full power!
Check Digi-Key also
73,
Charlie, K4OTV
P.S. I think you could avoid adding 5' of RG-8 or RG58 - but you could add
it in parallel with your 16o feed line via a Tee connector.
-----Original Message-----
From: Topband [mailto:topband-bounces@contesting.com] On Behalf Of Herb
Schoenbohm
Sent: Thursday, October 03, 2013 10:46 AM
To: TopBand List; towertalk@contesting.com
Subject: Topband: Fixed capacitor source needed (150pf 5KV)
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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