Hi, I wanted to follow up on this problem.
In response to my original post (below) a number of people responded that they were not seeing the behavior I described. After some more experimentation I found that the problem occurs primarily on 160 meters. On 160 meters, with my K3/KPA setup, the displayed KPA temp drops 5 to 6 deg C when transmitting in CW mode at 500 W. On all other bands the displayed temperature actually increases by 1 degree C -- not nearly as noticeable. I contacted a few of the guys who responded to my original post and asked them to try the experiment of transmitting at 500 watts on 160 and watching the TEMP display. So far I've gotten two responses with both reporting seeing a similar problem. So apparently this is a design flaw in the KPA's temperature measuring. With my KPA, when the amp gets in the temperature region where the fan kicks on, the bogus drop in temperature will turn the fan off. I don't think this would cause a serious overheating problem but it does cause the fan to cycle on and off with transmissions. Seems to me that this rapid on/off cycling can't be good for the fan. I've also come across two other K3/KPA bugs that may be of interest. 1) If you put the K3 into "SSB + CW" mode via the CW WGHT command and set the K3 to an SSB mode, the first CW transmission after a significant change in power level will be accompanied by a short power spike. The spike only occurs on the first transmission after the power level change. The size of the spike seems to vary with the band - with my setup it's pretty bad on 10 meters and very small on 20 meters. The KPA sees the spike and, depending on the size of the spike and/or how close the drive level is to maximum output, the spike can cause the KPA to fault. In any case, with the KPA in PK HOLD mode you can see its response to the spike. This particular problem caused me a lot of trouble before I finally figured out the exact circumstance and got Elecraft to verify that it's a design problem and not a problem with my particular K3 or KPA. Apparently it's a bug in the firmware ALC routine. They say their firmware guy is tied up with the KX3 but that he'll get to it as soon as he frees up. 2) Set the K3 up in the "per band" power mode such that the K3's STBY power is 100 W and OPER power is some reasonable drive level, say 20 watts. Set the KPA's BAND CHG menu item to STBY such that the KPA will switch to STBY when the band changes. Put the KPA into OPER mode. Change bands by hitting one of the KPA's BAND buttons. Go back to the original band. You'll find that the K3's STBY power for that band has been changed to the band OPER power - i.e. in this example, the original band's STBY power will have changed to 20 watts. Again, this appears to be a K3 firmware problem. The problem does not occur if you change bands by any other method other than the KPA's BAND buttons. Checking posts on the reflector I think I noticed some people commenting on seemingly random changes to "per band" power levels - this might be the cause. Anyway, hope this is of interest. 73, Mike - ke5akl ________________________________ From: Mike Walsh <ke5...@yahoo.com> To: "elecraft@mailman.qth.net" <elecraft@mailman.qth.net> Sent: Friday, February 10, 2012 12:28 PM Subject: Normal KPA500 behavior? Hi, My KPA500 does a couple of things that seem a bit odd. Other KPA owners - do your KPAs also do the following? 1) When I transmit a 500 watt carrier while displaying TEMP the displayed temperature drops 5 degrees C. When I release the key the temperature goes immediately back to the real value. Lower transmit power levels cause a correspondingly lower drop in displayed temp. This behavior causes the temp display to bounce around while transmitting CW. 2) When I power down my KPA the fan turns on (as it should) and then the right most POWER LED flashes on an off quickly. Is that LED flash normal? Thanks and 73, Mike - ke5akl ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
