If you do a search on e-bay for "capacitor doorknob" and you'll be surprised
at the values you find. I'm looking at one right now with 5 of the same
capacitors I used for $24.50 "Buy it now" price. Here is the link if you
want to look:
http://cgi.ebay.com/470-pF-16-KV-Doorknob-Capacitors-Brand-New-Lot-of-5_W0QQitemZ200422100559QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item2eaa168e4f
Ron N6IE
www.N6IE.com
----- Original Message -----
From: "John McAlpine IV" <kz4b@hotmail.com>
To: <tentec@contesting.com>
Sent: Tuesday, December 29, 2009 8:31 PM
Subject: Re: [TenTec] 238 caps
I have two Model 238 and two older Model 229 (electrically identical to
238 but earlier cosmetic design) TT Tuners to go with my two legal limit
TITAN 1 (425)'s and two Ameritron AL1500 Linears that I operate on both AM
& SSB.
Due to frequent (nominal 400 picofarad) disc ceramic switched "shunt"
capacitor failures--I have changed each of them out to small 5kV 400 pfd
"doorknob type capacitors mounted four in a row on the bottom of each of
the tuners in a line just under the central shaft connecting the capacitor
selector knob on the front panel to the shunt switch wafer at the back of
the tuner. These capacitors appear to fail due to high RF Current (they
get hot) and not excessive voltage. With this modification I have had zero
tuner failures of any kind even with challenging antennas and max legal
power with this mod in place.
The only problem with the above mod is the increasingly high cost of
ceramic doorknob type capacitors. I was very lucky in finding sixteen
blue-colored 5/8 inch diameter surplus doorknob capacitors at the Shelby
Hamfest approximately five years ago for only $5.00 each! I have NO extra
capacitors available for sale, don't remember the name of the Vendor, and
haven't confirmed any current sources. Try RF Parts and Surplus sales of
Nebraska for starters. Good luck in your hunt.
John R. McAlpine IV, P.E. / KZ4B 110 Lakefront DriveMooresville, N.C.
28117704-663-1364
Date: Tue, 29 Dec 2009 19:23:45 -0600
From: ranchorobbo@gmail.com
To: tentec@contesting.com
Subject: Re: [TenTec] 238 caps
I get it now, thanks Ron and Jim. I have not observed any trouble
with mine yet but I use it to tune my inverted L on 160 when I run a
250 w. carrier there. some of my transmissions get uh, relatively
long. the pep is around 1.2 kw. I may pull mine out and look inside
to see if there are any signs of stress. I smoked a supposedly legal
limit low pass filter a few months ago, the type that cuts off at 30
MHz, but in that case the failure was torroid inductors.. the caps,
similar to the ones in the 238 were all fine.
73
Rob
K5UJ
_______________________________________________
TenTec mailing list
TenTec@contesting.com
http://lists.contesting.com/mailman/listinfo/tentec
_______________________________________________
TenTec mailing list
TenTec@contesting.com
http://lists.contesting.com/mailman/listinfo/tentec
|