K2 Contest
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Hello all,
I am the lucky owner of a K2/100. I finished the amplifier part just about 2 weeks ago and did not have an antenna available at the moment for a decent test. This weekend we had the PACC contest and decide to use the K2 (basically for 40m CW) during the group activity. I didn't have any problem! But I'm curious to hear some comments on a K2 during contest/dx-pedition activities. During the activity on 40m the heatsink became rather warm (I guess about 45 deg) and felt a specific hot-spot (must be close to the power transistors). I switched the fan to full operation to ensure maximum cooling. But during the activity on 15m (with a good SWR) I noticed that the heatsink temp became at least 5 deg more then during 40m activity (efficiency reasons?). This experience drove me to ask the next questions: 1) Is there a noticeable difference in heat-sink temperature when operating on higher bands? 2) Can this amplifier be tuned for 1 hour on a dummy with full output at any band without any semi-irreversible side effects? 3) I'm used to big tube amplifiers which need air-flow "throughput". The fan in the K2 is blowing into the box but there is no way out (kind of short circuit in terms of air flow). What is the reason for this cooling fan to blow into the box instead of making "forced" airflow through/along the heatsink. It looks to me that some extra holes into the cabinet might raise the efficiency of cooling dramatically (inside the box) The 2 most important reasons for electronics to stop functioning is over voltage/current and temperature stress by cooling - heating - cooling - heating etc. Even if the heating is within the specs, the overall product life is degenerating quickly by extremely temperature changes. It also stresses the solder point on the PCB. In general: Is the K2 designed to operate at full specs during contests/expeditions under any normal environmental condition (0 deg C to 40 deg C) without cooling down periods? Evert, PA2KW K2 : SN4836 _______________________________________________ Elecraft mailing list Post to: [hidden email] 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 |
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> -----Original Message-----
> The fan in the K2 is blowing into the box but there is no way > out (kind of short circuit in terms of air flow). Hi, Evert I wondered about the same when I built my KAP100, and here is an explanation from the Elecraft reflector some years ago: Subject: Re: [Elecraft] KPA100 Fan Question From: Eric Swartz WA6HHQ - Elecraft <[hidden email]> Date: Sun Dec 15 19:12:01 2002 List-post: <mailto:[hidden email]> Hi Ron, The air exits the case at the top of the K2/100 at the front between the heatsink fins. It does an excellent job of stabilizing the K2's internal temperature. If you still want to add auxilary cooling a 3" fan running at half speed placed on top of the heatsink (halfway to the rear and 2/3 to the right) pulling air up and away fromthe heatsink works well. Putting rubber stick on feet on the bottom of the fan will keep it in place and space it correctly for proper air flow. 73, Eric WA6HHQ _______________________________________________ Elecraft mailing list Post to: [hidden email] 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 |
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In reply to this post by Evert Bakker (PA2KW)
Evert wrote:
2) Can this amplifier be tuned for 1 hour on a dummy with full output at any band without any semi-irreversible side effects? ---------------------------------- If you mean at the rated output for 100% duty cycles modes, 40 watts out, the answer is Yes. But I'd not try it at 100 watts. The 100 watt spec assumes you are running SSB or CW that has a much, much lower duty cycle, so the average power output remains 40 watts or less. Several years ago I helped test the VCO stabilization mod and needed to temperature-cycle the K2 as in normal heavy use. I did that be transmitting into a dummy load for periods of 1/2 hour to 1 hour, occasionally longer. I ran the K2 at 100 watts and keyed it in CW, using a repeating CW memory to keep it running. The internal air temperature between the KPA100 and main K2 PCB got up over 50C (120F). The KPA100 heat sink was too hot to hold my hand on it. Since the intent was to simulate very heavy use of the rig in a real situation, I did not provide any ancillary cooling. I did that dozens of times. No problems were encountered. I did not run those tests on various bands, so I can't speak to any significant temperature differences. But there are some slight differences in efficiency. Does your KPA100 make a full 100 watts output on all bands? If not, there might be a problem with your output filter on one or more bands that is reducing the efficiency more than it should. That would produce excess heat as well. If you are getting full rated output, I'd expect that any differences noted are normal. Be sure to tighten your final PA transistor mounting screws after several hours of operation as described in the manual. That ensures you maintain the intimate mechanical contact needed for efficient heat transfer. It only needs to be done once. I think my screws took about 1/2 turn after the rig was run in for several hours, then they remained "snug". As others have pointed out, there is exit cooling cleverly hidden between the fins on the KPA100 heat sink at the forward end. So if you use the heat sink to keep your coffee cup warm, don't spill any! Ron AC7AC _______________________________________________ Elecraft mailing list Post to: [hidden email] 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 |
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This is what I like the most about Elecraft. You have persons like Wayne,
Ron, Tom, and Don coming out and freely giving this technical information. One would never see Yaesu or Kenwood or Icom doing this. Thanks Guys for the knowledge and the helpfulness. john-n3drk ----- Original Message ----- From: "Ron D'Eau Claire" <[hidden email]> To: "'Elecraft e-mail reflector'" <[hidden email]> Sent: Sunday, February 12, 2006 12:36 PM Subject: RE: [Elecraft] K2 Contest Evert wrote: 2) Can this amplifier be tuned for 1 hour on a dummy with full output at any band without any semi-irreversible side effects? ---------------------------------- If you mean at the rated output for 100% duty cycles modes, 40 watts out, the answer is Yes. But I'd not try it at 100 watts. The 100 watt spec assumes you are running SSB or CW that has a much, much lower duty cycle, so the average power output remains 40 watts or less. Several years ago I helped test the VCO stabilization mod and needed to temperature-cycle the K2 as in normal heavy use. I did that be transmitting into a dummy load for periods of 1/2 hour to 1 hour, occasionally longer. I ran the K2 at 100 watts and keyed it in CW, using a repeating CW memory to keep it running. The internal air temperature between the KPA100 and main K2 PCB got up over 50C (120F). The KPA100 heat sink was too hot to hold my hand on it. Since the intent was to simulate very heavy use of the rig in a real situation, I did not provide any ancillary cooling. I did that dozens of times. No problems were encountered. I did not run those tests on various bands, so I can't speak to any significant temperature differences. But there are some slight differences in efficiency. Does your KPA100 make a full 100 watts output on all bands? If not, there might be a problem with your output filter on one or more bands that is reducing the efficiency more than it should. That would produce excess heat as well. If you are getting full rated output, I'd expect that any differences noted are normal. Be sure to tighten your final PA transistor mounting screws after several hours of operation as described in the manual. That ensures you maintain the intimate mechanical contact needed for efficient heat transfer. It only needs to be done once. I think my screws took about 1/2 turn after the rig was run in for several hours, then they remained "snug". As others have pointed out, there is exit cooling cleverly hidden between the fins on the KPA100 heat sink at the forward end. So if you use the heat sink to keep your coffee cup warm, don't spill any! Ron AC7AC _______________________________________________ Elecraft mailing list Post to: [hidden email] 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 _______________________________________________ Elecraft mailing list Post to: [hidden email] 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 |
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