[Elecraft] KX-3 TX current draw?

[Drew Arnett]

Just to follow up.  When I talked to support, they recommended sending
in for service.

After getting the rig back, I've only used it for IF at 100 mW on 50
MHz with transverter.  And had a weird loud audio buzz problem.  See
separate email describing that.  Have reported to Elecraft; still
waiting for a response.  Assuming the buzz problem is unrelated,
here's a set of new measurements made this morning to show post repair
performance for TX.

ATU bypassed.  Bench DC supply.  Excellent dummy load.  No coax, just
a couple of coax adapters between rig and dummy load.

14 MHz @ 1 W setting
13.6 V RX (per KX3)
13.4 V TX (per KX3)
0.660 A TX (per KX3)
VSWR 1.0 (per KX3)

28 MHz @ 1 W setting
13.6 V RX
13.4 V TX
0.765 A TX
VSWR 1.0

50 MHz @ 1 W setting
13.6 V RX
13.2 V TX
1.040 A TX
VSWR 1.5

50 MHz @ 4 W setting
13.6 V RX
13.0 V TX
1.710 A TX
VSWR 1.6

That looks MUCH better.  Efficiency on 50 MHz @ 4 W is > 18% and on
par with the one other reported measurement.

Huge thanks to Elecraft for getting the repair done before my next
major contesting event, the first weekend of the 10 GHz and Up.  (Hmm.
Some HF contesting coming up soon.  Amazing how many different kinds
of fun you can have with a KX3!)

I am a bit disappointed with the SWR meter on 50 MHz.  Makes me wonder
how to operate safely on 50 MHz without an external meter or when
using the internal ATU.

FYI if anyone else runs into this issue, the repair report:
     Repair(s) performed:
     Replaced Q6-Q7 (E850047)
     Current draw at 2.90 amps or below is acceptable.
     -
     Updates performed:
     Control panel:
     Updated firmware.
     Updated Q9 (part change)
     RF Board:
     Replaced C1U and C1P (value change)

Best regards,

Drew
n7da

On Sat, May 16, 2020 at 5:25 PM Drew Arnett <arnett.drew at gmail.com> wrote:
>
> To follow up on Victor's point, did some more measurements this morning.
>
> Setup:
> KX-3 minimal adapters to 40 dB directional coupler to load
> terminated unused port of coupler
> measured port through 3 ft patch to Kanga US AD8307 RF power meter
>
> I have good calibration data for the power meter, but for the purpose
> at hand, I won't correct the meter readings.  60 on the scale is about
> -20 dBm.  Every 10 on the scale is actually 10.7 dB.  Good enough.
>
> Internal tuner bypassed.
>
> Measurements:
>
> Note:  RX current in RX was between about .15 and .19 A for all 3 bands.
>
> 14 MHz @ 1 W setting
> 13.7 V RX (per KX3)
> 13.4 V TX (per KX3)
> 1.15 A TX (per KX3)
> VSWR 1.3 (per KX3)
> FWD 67 (on power meter display, very close to expected)
> REV 30 (on power meter display)
> --> return loss approx 37 dB
>
> 28 MHz @ 1 W setting
> 13.7 V RX
> 13.4 V TX
> 1.15 A TX
> 1.3 VSWR
> FWD 67
> REV 30
> --> return loss approx 37 dB
>
> 50 MHz @ 1 W setting
> 13.7 V RX
> 12.9 V TX
> 2.9 A TX
> 1.6 VSWR
> FWD 71
> REV 35
> --> return loss approx 36 dB
>
> Hmm.  So, I'm seeing 3% or less efficiency.  Only one respondent on my
> query about TX current draw, and he was getting 15%+ efficiency.  No
> wonder my PA temp shoots up.
>
> Thanks,
>
> Drew
> n7da
>
> On Sat, May 9, 2020 at 11:25 AM Drew Arnett <arnett.drew at gmail.com> wrote:
> >
> > Good point, Victor.  And why I included that SWR reading.  Other bands
> > read fine.  I have high confidence in the load and adapter (tried
> > swapping both just in case).  I could measure the load and adapter the
> > next time I'm in the lab at work if I want to be absolutely thorough,
> > but it is a microwave load and just adapting from BNC to N (no coax).
> >
> > SWR looks fine on other bands.
> >
> > Thanks,
> >
> > Drew
> > n7da
> >
> > On Sat, May 9, 2020 at 4:57 AM Victor Rosenthal <k2vco.vic at gmail.com> wrote:
> > >
> > > I think 1.6:1 is high for that kind of dummy load, if it's in good shape. Should be close to 1:1.
> > > Anyway, you can't really say there is a problem unless you have a better match. Current draw is sensitive to mismatch.
> > > --
> > > Vic
> > >
> > > On May 9, 2020 2:32:15 AM GMT+03:00, Drew Arnett <arnett.drew at gmail.com> wrote:
> > >>
> > >> Walter,
> > >>
> > >> 50 MHz TX constant 4 W carrier measures 13.53 V on DMM (outside the DC
> > >> power plug), 13.3 V on KX3 meter, 2.9 A on KX3 meter and 1.6 to 1 VSWR
> > >> on KX3 meter.  Microwave dummy load with BNC to N adapter.
> > >>
> > >> I didn't measure all of this when the rig was new, so have no baseline
> > >> to know what is normal.  :-(
> > >>
> > >> Thanks,
> > >>
> > >> Drew
> > >> n7da
> > >>
> > >> On Fri, May 8, 2020 at 11:19 PM Drew Arnett <arnett.drew at gmail.com> wrote:
> > >>>
> > >>>
> > >>>  What do you see for current draw on the KX-3?  Manual says 1 to 2 A typical.
> > >>>
> > >>>  I'm seeing 3 A at less than full power on one band.  Yikes!  Makes me
> > >>>  wonder if the repair shop is open?  Elecraft website says hunkered
> > >>>  down and mostly work from home.
> > >>>
> > >>>  Thanks and best regards,
> > >>>
> > >>>  Drew
> > >>>  n7da
> > >>
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