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
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