K2 current draw
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I just noticed an interesting thing about my K2/100: the current drawn by the
low-power part of the K2 (that's the current measured when you tap DISPLAY) is extra high on one band: 20 meters. When I'm running 100 watts out, the current displayed varies from about 2.2-2.8 amps on all bands other than 20. On 20, it's 3.5 amps. My first thought was that the bandpass filter was misaligned on 20. Sure enough, after adjusting L7 and L8 on 30 meters, the 20-meter trimmers were at minimum capacity when the output peaked. I had to add an 8 pf capacitor across one of them and a 27 pf capacitor (!) across the other in order to have the peak fall in the adjustment range of the trimmer. Very suspicious. After doing this, I verified that the current draw when running 10 watts on 20 meters was in line with the other bands. But when running 100 watts, I still get 3.5 amps! Something funny is going on. Why was I unable to get a peak on 20 without extra capacity across the bandpass filter trimmers? And why is the current drawn at 10 watts normal, but high at 100 watts? This is not something new, I've just ignored it until now! -- 73, Vic, K2VCO Fresno CA http://www.qsl.net/k2vco _______________________________________________ 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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Vic,
There are only 2 things that have potential for causing higer drive requirements on 20 meters - the base K2 low pass filter and the base circuit of the KPA100. I have not noticed any problem with 20 meters on all the KPA100s that I have worked on (but I follow the manual recommendation to set CAL CUR to 3.5 Amps, and I look no further), so I suggest that you look carefully at the resistors and capacitors in the base circuit of the KPA100 and count the turns on the toroids for the 20/30 meter portion of the K2 LPF - my bet is that you can 'tweak' the windings in the K2 LPF to improve the situation - one extra turn on a toroid (L18, L19 or L20) can lower the frequency enough to reduce to power output per ampere (actually increse the current draw) from the base K2 on 20 meters, and not be noticable under any other conditions - the load presented by the KPA100 is not precisely 50 ohms on all bands, hence my suggestion to investigate the base circuit. OTOH, the KPA100 manual recommends that the CAL CUR be increased to 3.5 Amps when the KPA1000 is installed, so things are still within expectations, but with fine tuning, you may be able to do better than average. 73, Don W3FPR > -----Original Message----- > > I just noticed an interesting thing about my K2/100: the current > drawn by the > low-power part of the K2 (that's the current measured when you > tap DISPLAY) is > extra high on one band: 20 meters. When I'm running 100 watts > out, the current > displayed varies from about 2.2-2.8 amps on all bands other than > 20. On 20, > it's 3.5 amps. > > My first thought was that the bandpass filter was misaligned on 20. Sure > enough, after adjusting L7 and L8 on 30 meters, the 20-meter > trimmers were at > minimum capacity when the output peaked. I had to add an 8 pf > capacitor across > one of them and a 27 pf capacitor (!) across the other in order > to have the peak > fall in the adjustment range of the trimmer. Very suspicious. > > After doing this, I verified that the current draw when running > 10 watts on 20 > meters was in line with the other bands. But when running 100 > watts, I still > get 3.5 amps! > > Something funny is going on. Why was I unable to get a peak on > 20 without extra > capacity across the bandpass filter trimmers? And why is the > current drawn at > 10 watts normal, but high at 100 watts? > > This is not something new, I've just ignored it until now! > > No virus found in this outgoing message. Checked by AVG Anti-Virus. Version: 7.0.308 / Virus Database: 266.11.10 - Release Date: 5/13/2005 _______________________________________________ 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 Vic K2VCO
Vic
The bandpass filter alignment merely assures you have adequate drive to the PA. The LPF will have more effect on the PA current, as it determines whether you have a match between the load the and PA. 73, Bob N6WG -----Original Message----- From: elecraft-bounces+n6wg=[hidden email] [mailto:elecraft-bounces+n6wg=[hidden email]]On Behalf Of Vic Rosenthal Sent: Sunday, May 15, 2005 3:39 PM To: Elecraft Reflector Cc: Gary Surrency Subject: [Elecraft] K2 current draw I just noticed an interesting thing about my K2/100: the current drawn by the low-power part of the K2 (that's the current measured when you tap DISPLAY) is extra high on one band: 20 meters. When I'm running 100 watts out, the current displayed varies from about 2.2-2.8 amps on all bands other than 20. On 20, it's 3.5 amps. My first thought was that the bandpass filter was misaligned on 20. Sure enough, after adjusting L7 and L8 on 30 meters, the 20-meter trimmers were at minimum capacity when the output peaked. I had to add an 8 pf capacitor across one of them and a 27 pf capacitor (!) across the other in order to have the peak fall in the adjustment range of the trimmer. Very suspicious. After doing this, I verified that the current draw when running 10 watts on 20 meters was in line with the other bands. But when running 100 watts, I still get 3.5 amps! Something funny is going on. Why was I unable to get a peak on 20 without extra capacity across the bandpass filter trimmers? And why is the current drawn at 10 watts normal, but high at 100 watts? This is not something new, I've just ignored it until now! -- 73, Vic, K2VCO Fresno CA http://www.qsl.net/k2vco _______________________________________________ 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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