Your description is typical of some component or components heating and
changing value. This is not uncommon with this tuner, but usually with
higher power. Three areas of concern are; (a) the 4 parallel pairs of
220pf capacitors which are switched by the HI LO Z switch. (b) the
internal balun, and (c) the series combination of C7 & C8.
My solution to all of this is replace the capacitors and balun.
(a) use 470pf doorknob capacitors, 4 of them, to replace the 4 pairs
of 220pf disk ceramic capacitors. Tight fit but can be put in on the
base plate at the rear and keep the leads short. Requires drilling 4
holes in the bottom plate to mount the capacitors direct to the bottom
plate.
(b) replace the series pair C7 & C8 with a 25pf doorknob capacitor
mounted on the rear panel. Requires drilling 1 hole. And a short jumper
to the HI LO Z switch.
(c) forget about using the internal balun. I use a Balun Designs 1:1
balun model 1171T. An 18" coax jumper connects the balun to one of
the SO-239 outputs. Balun sits on top of the tuner. The balanced
feedline runs from the feed point of the antenna all the way to the
balun. No long coax jumper is used.
Further your description of the extra required capacitors and heating
are clear indication you are using the wrong balun. A 4:1 balun will
transform the antenna impedance to a Z value divided by 4. Thus the
tuner has to match a low impedance which is the values where loss is
greatest. Thus if your antenna feed Z is 35 ohms, the 4:1 balun will
transform that Z to 8.75 ohms, which is what the tuner must match. Hi
Z load impedance has less loss internally. Many hams believe,
incorrectly so, that a 4:1 balun should be used with a balanced
feedline, i.e. 450 ohms. This is absolutely incorrect. You are not
matching the feedline but the antenna Z.
Problem solved, all bands, and up to legal limit high duty cycle power.
73
Bob, K4TAX
On 7/21/2018 2:26 AM, Peter Klein wrote:
I've just noticed something interesting about my Ten Tec 229B tuner.
It happens on 80m-30m, where the center switch is in positions Lo2 -
Lo5 and various fixed capacitors are switched into the circuit.
I use non-resonant antennas fed with ladder line. I normally tune the
tuner with a noise bridge or at 10 watts. Then, when I operate at 100
watts, I notice a slight upward creep of SWR over a few seconds after
key-down. Then the SWR backs down a little and remains stable while
I'm transmitting. The creep is very slight, from 1:1 up to maybe 1.2
or 1.3:1 on my IC-7300's SWR meter. My guess is that this is the same
issue some people report with the Ten Tec tuners on 160m. On low
impedance loads that require the extra fixed capacitors to switch in,
those capacitors warm up slightly and change value as we transmit.
I never noticed this before. But I just picked up a used Daiwa
CN-101L cross-needle SWR meter, because the tuner's switched meter and
the IC-7300's multiple displays make monitoring SWR inconvenient. The
Daiwa's "reflected" readings are a bit overly sensitive. On that
meter, I could clearly see the creep happening. Sure enough, when I
looked on my IC-7300's SWR meter, it was happening there, too. The Ten
Tec tuner's meter barely shows it, if at all.
My guess is that everything is fine. The SWR creep is too small to
endanger my finals, and I can always touch up the tuning. I just want
to be sure that the SWR creep doesn't indicate that the fixed
capacitors in the tuner are failing. Can someone give me a reality check?
Thanks and 73,
--Peter, KD7MW
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