RE: [Elecraft] K2/100 current consumption problem - update
Just a quick note to say thanks to everyone for their help and suggestions. I'm affraid I haven't yet got to the bottom of this (excessive current at full power on topband on our club's K2). I could not find anything wrong component/construction wise, but for now I have too many other things to do. For the moment I've turned back the internal power control pot. This means the power display is no longer calibrated and the rig gives circa 90W out when set for 110. This is not a big deal in practice and it stops the problem happening. I suspect, (as G4PIQ suggested) that the power sense circuitry drops off in sensitivity on topband. 73 Fraser G4BJM _ Express yourself with cool new emoticons http://www.msn.co.uk/specials/myemo ___ 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
Re: [Elecraft] K2/100 current consumption problem - update
So far I haven't found anything wrong as such on #3764: The LPF components appear fine (value and condition), and check out ok with an MFJ analyser for SWR on receive. T1 and T2 and associated components appear ok. One thing; C83 is 1000pF, not 1200pF as per circuit. However I tried padding that with a 220pF SM and it made no difference. Looks like 1000pF was supplied with the kit. I've realigned the BPF on 160/80m, which was pretty much ok anyway. I've re-adjusted the bias, which was also ok. I've readjusted the pwr sense pot, again was ok. With the PA disabled the base K2 draws about 2.5A @ 10W op on all bands. With the PSU set to exactly 13.8V, and measuring the current (V across 10x0R1 6W in parallel, in series with V+) I get the following, into a 50R load. Current on the PSU display reads similar. Set power W Current A 160m Current A 80m 5014 14 6015 15 7016.516.5 8018 18 90 24 19 100 27 20 110 29 21 The actual power out is similar to the set power, to about 10%.So topband behaves ok up to about 80W op. This also happens from a cold start, so I don't think it's thermal runaway. No instabilities are apparent on a scope or spec. an. Any suggestions appreciated. Thanks / 73 Fraser G4BJM _ It's fast, it's easy and it's free. Get MSN Messenger today! http://www.msn.co.uk/messenger ___ 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
Re: [Elecraft] K2/100 current consumption problem - update
Fraser, This is a very very long shot and probably daft! I see that the current drawn on 160m tracks that drawn on 80m until the RF output passes 80w.going up.From this I think that it is safe to say that the bad KPA100 is working as it should to that power output level. Above that it is either starting to flat-top for X reasons or its standing DC bias is changing perhaps towards Class A or the driver has run out of steam. Let me focus on bias change. Is it poissible that 160m RF above a certain output power level mucks up the PA bias oscillator or that some circuit(s) in the bias supply resonate at 160m thereby changing the DC bias to the PA.? There is a lot of PA output RF around, but it might be worthwhile to measure the DC bias voltage as you run up the PA power. Capacitor tolerances alone would move such resonances around greatly. Just a thought. 73, Geoff. GM4ESD - Original Message - From: Fraser Robertson [EMAIL PROTECTED] To: elecraft@mailman.qth.net; [EMAIL PROTECTED] Cc: [EMAIL PROTECTED] Sent: Thursday, March 03, 2005 2:21 PM Subject: Re: [Elecraft] K2/100 current consumption problem - update So far I haven't found anything wrong as such on #3764: The LPF components appear fine (value and condition), and check out ok with an MFJ analyser for SWR on receive. T1 and T2 and associated components appear ok. One thing; C83 is 1000pF, not 1200pF as per circuit. However I tried padding that with a 220pF SM and it made no difference. Looks like 1000pF was supplied with the kit. I've realigned the BPF on 160/80m, which was pretty much ok anyway. I've re-adjusted the bias, which was also ok. I've readjusted the pwr sense pot, again was ok. With the PA disabled the base K2 draws about 2.5A @ 10W op on all bands. With the PSU set to exactly 13.8V, and measuring the current (V across 10x0R1 6W in parallel, in series with V+) I get the following, into a 50R load. Current on the PSU display reads similar. Set power W Current A 160m Current A 80m 5014 14 6015 15 7016.516.5 8018 18 90 24 19 100 27 20 110 29 21 The actual power out is similar to the set power, to about 10%.So topband behaves ok up to about 80W op. This also happens from a cold start, so I don't think it's thermal runaway. No instabilities are apparent on a scope or spec. an. Any suggestions appreciated. Thanks / 73 Fraser G4BJM ___ 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
Re: [Elecraft] K2/100 current consumption problem - update
Fraser Robertson wrote: One thing; C83 is 1000pF, not 1200pF as per circuit. However I tried padding that with a 220pF SM and it made no difference. Looks like 1000pF was supplied with the kit. Hi Fraser, The change from 1200 to 1000 was made after the field test. It improves efficiency on 10 meters. It shouldn't have any effect on 160. 1000 is correct. I admit to being mystified by your problem! -- 73, Vic, K2VCO Fresno CA http://www.qsl.net/k2vco ___ 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
Re: [Elecraft] K2/100 current consumption problem - update
Thanks Geoff, the TR bias HV is 139V on RX. On TX at 70W out it's about 118V on 160m and 80m. With power flat out it's 113V on 80m and 109V on 160m. So I think that's ok. The voltage on U7B pin 5 and 6 is identical on 160m and 80m at full power at 675mV, so I think the PA bias current is behaving. G3VTT suggested the transformers, but they have the correct number of turns, including the po/swr sensor T4. Thanks / 73 Fraser G4BJM From: Geoffrey Mackenzie-Kennedy [EMAIL PROTECTED] To: Fraser Robertson [EMAIL PROTECTED] CC: Elecraft Discussion List elecraft@mailman.qth.net Subject: Re: [Elecraft] K2/100 current consumption problem - update Date: Thu, 3 Mar 2005 15:26:48 - Fraser, This is a very very long shot and probably daft! I see that the current drawn on 160m tracks that drawn on 80m until the RF output passes 80w.going up.From this I think that it is safe to say that the bad KPA100 is working as it should to that power output level. Above that it is either starting to flat-top for X reasons or its standing DC bias is changing perhaps towards Class A or the driver has run out of steam. Let me focus on bias change. Is it poissible that 160m RF above a certain output power level mucks up the PA bias oscillator or that some circuit(s) in the bias supply resonate at 160m thereby changing the DC bias to the PA.? There is a lot of PA output RF around, but it might be worthwhile to measure the DC bias voltage as you run up the PA power. Capacitor tolerances alone would move such resonances around greatly. Just a thought. 73, Geoff. GM4ESD - Original Message - From: Fraser Robertson [EMAIL PROTECTED] To: elecraft@mailman.qth.net; [EMAIL PROTECTED] Cc: [EMAIL PROTECTED] Sent: Thursday, March 03, 2005 2:21 PM Subject: Re: [Elecraft] K2/100 current consumption problem - update So far I haven't found anything wrong as such on #3764: The LPF components appear fine (value and condition), and check out ok with an MFJ analyser for SWR on receive. T1 and T2 and associated components appear ok. One thing; C83 is 1000pF, not 1200pF as per circuit. However I tried padding that with a 220pF SM and it made no difference. Looks like 1000pF was supplied with the kit. I've realigned the BPF on 160/80m, which was pretty much ok anyway. I've re-adjusted the bias, which was also ok. I've readjusted the pwr sense pot, again was ok. With the PA disabled the base K2 draws about 2.5A @ 10W op on all bands. With the PSU set to exactly 13.8V, and measuring the current (V across 10x0R1 6W in parallel, in series with V+) I get the following, into a 50R load. Current on the PSU display reads similar. Set power W Current A 160m Current A 80m 5014 14 6015 15 7016.516.5 8018 18 90 24 19 100 27 20 110 29 21 The actual power out is similar to the set power, to about 10%.So topband behaves ok up to about 80W op. This also happens from a cold start, so I don't think it's thermal runaway. No instabilities are apparent on a scope or spec. an. Any suggestions appreciated. Thanks / 73 Fraser G4BJM _ It's fast, it's easy and it's free. Get MSN Messenger today! http://www.msn.co.uk/messenger ___ 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
RE: [Elecraft] K2/100 current consumption problem - update
Fraser, If you have a 'scope handy, try cranking the power up to 100 watts on 160 and 80 and observing the CW envelope - if you see what looks like weak modulation on the top and bottom of the envelope pattern, you have a low frequency oscillation. If you do have that oscillation, the 'cure' has been discussed on this reflector - on the KPA100, put a 1K resistor across RFC3, and change R4 from 100k to 39k. I have worked on KPA100s having this modulation problem, but never related it to current draw before, but it is worthy of investigation. 73, Don W3FPR -Original Message- Thanks Geoff, the TR bias HV is 139V on RX. On TX at 70W out it's about 118V on 160m and 80m. With power flat out it's 113V on 80m and 109V on 160m. So I think that's ok. The voltage on U7B pin 5 and 6 is identical on 160m and 80m at full power at 675mV, so I think the PA bias current is behaving. G3VTT suggested the transformers, but they have the correct number of turns, including the po/swr sensor T4. Thanks / 73 Fraser G4BJM ___ 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
