Have you calibrated the KPA100 temperature sensor and set the quiescent bias?
The KPA100 has a self-protection circuit in it that reduces power and displays the message "PA HOT" if the heat sink temperature exceeds 85C (185F). I'm not sure it's possible to get the heat sink that hot in normal use, even the most long winded rag chews <G>. A few years ago I was part of a group testing the stability of the K2/100 over a wide range of operating temperatures. The test protocols included loading a message buffer with CW, then sending nonstop for between 30 and 60 minutes at 100 watts output. Under those conditions, in a shack with an ambient temperature of 24C (75F) the temperature of the cooling fins on the heat sink would approach 50C (122F). The K2 cooling fan was operating normally automatically switching to "high" above 37C (100F). No other cooling was provided. The tests were done dozens of times with no adverse effects on the rig. Eventually the heat sink temperature reaches equilibrium. The greater the difference between its temperature and the ambient air temperature, the faster it loses heat. When the loss of heat equals the heat being contributed by the amplifier circuits, the temperature no longer rises. The testing did not try to find this equilibrium. We were testing the effects on the heat on internal oscillators, not testing the KPA100 itself. My notes do indicate that the rise beyond 50C was very, very slow, however. That's why the tests stopped there. The rig was no longer heating appreciably. I mention the quiescent bias because the current the PA transistors are drawing "key up" also contributes heat. If it's high, that could lead to significant additional heating. Ron AC7AC -----Original Message----- Jim, I run alot of CW contests and with constant CQing/exchanges you could fry an egg on the heatsink. The existing cooling cannot keep up with the heat generated. It looks a bit Frankenstein but I mounted (with double back tape) a 12 volt 2.5" muffin fan on top of the heat sink. It runs cool as a cucumber now. This is now standard operating procedure for contests I run at 100w. Jay - KT5E Jim Stoneback wrote: > I searched the archives and didn't find anything on this, but from > what I've read, I think I may have a problem with my KPA100. When > operating CW the fan turns on high during every transmission and the > heat sink gets hot to the touch. I'm a ragchewer so my transmissions > do run to several minutes and, regardless of power setting, the fan > will kick on high after several minutes of transmitting. Fan is set > to 'nor'. Sending speed ranges from 15-20 wpm. Ambient temperature > in the shack is around 74F. The fan has never kicked up to high when > on SSB but I don't operate fone much, and generally don't talk for > very long when I do. The K2/100 (recent build, sn 6194, KPA100 > Version F1.10) operates well in all other respects. Does anyone have > an idea what may be wrong? _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
