[Elecraft] Intermittent low output KPA500

[Jack Brindle]

Place a watt meter between the transceiver and the KPA500 and measure the TX output into the KPA. I think you will find the transceiver output is low at those times.

This is fairly common in the K3/K3S world when the tx needs to be recalibrated. I would suggest that your 7610 may need recalibration as well.

The KPA500 is a linear amplifier - it has fixed gain. The only thing in the KPA500 that could change the gain is a 3db pad in the front end that is invoked when the controller sees something amiss, but not so bad as to declare a fault (yet). You would see a flashing red LED on the KPA when this is invoked. Since you didn’t mention a flashing LED on the KPA, I can only assume the pad is not being invoked. This then points at the driving tx for low output.

73,
Jack, W6FB


> On Apr 16, 2025, at 1:01 PM, Phil Zminda via Elecraft <elecraft at mailman.qth.net> wrote:
> 
> In the last few days I have noticed that when operating FT8 using my KAT500/KPA500 combo with an IC-7610, my output seems low on the first or second transmit cycles after switching bands. If I am chasing DX I usually run about 120 to 160 Watts, which is about 6 to 8 Watts on the transmitter. I am seeing only 50 or 60 Watts on the amp when I first transmit. After a couple cycles it goes to the higher output and is stable after that.
> 
> When changing bands, I switch the radio, with the amp in Standby, then switch bands on the amp before transmitting. Sometimes I use Tune in WSJT-X running just a few watts with the amp in Standby for the amp to automatically switch bands. My antennas have low SWR on most bands, so the tuner is often in Bypass. 
> 
> This seems to have just started and most often occurs on 20 Meters using a GAP 20 Meter Mono-band. 
> 
> I also run CW and some SSB but don’t notice the power meter as much as on FT8. I don’t thing it’s happening there.
> 
> Has anyone seen this or a similar problem? 
> 
> Phil N3ZP
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