[TenTec] Model 238 Tuner problems?

[Robert & Linda McGraw K4TAX]

More details.

These are specific observations with my 238 tuner while running some 1200 to
1500 watts of power, using a center fed 1/2 wave dipole fed with 1/2
electrical wavelength of RG-213 coax.  The antenna is resonate at about
3950.  While using the tuner to achieve a low SWR at frequencies below 3600
no problem, at frequencies above 3800 no problem.  HOWEVER, between 3600 and
3800 using a "key down" mode such as RTTY, the SWR would rise rapidly.
Retuning did corrected the problem. But then after 2 or 3 minutes in standby
the SWR was back up.  As I transmitted then SWR came down.  I.E.  heating
and cooling of some component(s).

With the cover off of the tuner, I carefully transmitted for 1 min, turned
the transmitter off and touched each component.  When you find the right
one.....OUCH!  It was very hot.  Removed it and replaced it with a
transmitting type capacitor of the same value.  These are mica capacitors
and are about 1.75" long x 1.5" wide, and about 0.5" thick.  There is a
screw terminal at each end for connection.  These are rated a 1KV .......but
have a RF current rating of some 2 amps.

Problem solved.

73
Bob K4TAX

----- Original Message -----
From: "Duane A Calvin" <ac5aa@juno.com>
To: <tentec@contesting.com>
Sent: Monday, October 01, 2001 1:03 PM
Subject: Re: [TenTec] Model 238 Tuner problems?


>
> Since a couple of folks have mentioned it I should add that I'm not using
> the balun.  This is strictly coax-to-coax matching.  One antenna is a
> Butternut HF2V which I run on 160m (500W max), 80m, 40m, 15m and
> sometimes 17m.  The other ant is a G5RV Jr. which I use on 30m, 20m, 12m
> and 10m.
>
> So far, most responses have suggested checking common coax (I have 2
> jumpers from amp, to Autek meter, to 238).  Good idea since I'd like to
> replace the mini-8X with full sized RG-8U.  One response indicated
> catastrophic failure of caps at the Z-switch (10m high power), and
> another was a 2nd hand report of someone having solder melting problems
> when used with wire antennas.
>
>         Duane
>
> Duane Calvin, AC5AA
> Austin, Texas
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