[Elecraft] K3 output power spikes

[Jim Sheldon]

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 at mailman.qth.net>
To: elecraft at 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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