Thanks David for posting this. I noticed this from time to time with my
old K3 and now also with the new K3S. I keep the KPA500 output set to
around 400-450 watts most of the time and notice spikes to 550 or so on
the first or second dit when sending CW at times. I just built the kit
and have done the TX calibrations properly and they all passed via the
Utility program.
I'm using the factory supplied #12 gauge power cable and the power
supply is a pretty well regulated MFJ 4245MV switcher (RFI quiet here).
This supply is adjustable and evidently the meter isn't totally accurate
or there is a larger voltage drop in the cable than I thought there
should be. I checked the K3S' meter display after receiving this email
and it read 13.2 volts. Keyed to 13.8 volts on the meter, but at 20
watts out, driving the amplifier, it dropped to 12.6 volts while keyed.
In line with your findings, I set the MFJ supply to read 13.8 volts on
the K3S display and it now only drops to 13.3 volts under the 20 watt
load. The occasional power spikes seem to have disappeared, so it's
something everyone should take a look at if they do experience the power
spike problem.
Again, thanks for posting this David.
Jim - W0EB
Park City, KS
------ Original Message ------
From: "David via Elecraft" <elecraft@mailman.qth.net>
To: elecraft@mailman.qth.net
Sent: 3/1/2016 5:40:46 AM
Subject: Re: [Elecraft] K3 output power spikes
My K3 s/n 4487 has exhibited similar behaviour since I built it in
2010.
Despite calls to Elecraft Support no solution was found despite Gary
talking
me through various items until a month or so ago when the spike was
causing
problems with my amp on 24 Mhz. It was mentioned that the K3 must see
13
volts whenever it is transmitting and to check this on the front panel
by
tapping the Display button. Mine showed 13.6 volts on receive and 12.6
volts
on Tx. Turned out my old power supply regulation was faulty. Anyway
after a
power supply rebuild and further check it now shows 13.6 volts on
receive
and 13.3 volts on Tx at 100 watts output. A further TX calibration
completed
the process and so far no power spikes! So check your power supply is
supplying sufficient voltage on key down.
Dave G0AIX
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