+++++++++++++++++++++++++++++++++++++++ Date: Fri, 06 Apr 2001 08:37:01 -0700 From: Eric Swartz WA6HHQ - Elecraft Subject: Re: [Elecraft] No 30/20 output on K2 #1981 Hi Randy, Executive Summary: Low Power + High Current on only 20/30M = Check the 20/30M LPF for faults. Since you only have low power only on a couple of bands, the Band Pass (BPF) and Low Pass (LPF) filter sections would be the most likely candidates. 20/30M share their BPF/LPF filter sections, as do 17/15 and 12/10. 160/80 share their BPFs but have separate LPFs. 40M has a separate BPF and LPF from the others. You mentioned rewinding T2, which can't hurt but as you noted was not the problem. T2, when its secondary windings are scrunched too close together, tends to roll off power output (with LOWER current drain) on 15M and above. So its effect is more gradual and usually not limited to just two bands. **** So, if you have low power output with HIGH current (on only two related bands) the LPF is the most likely culprit. You need lots of drive through the working BPF into the PA section to get the high current, so the LPF must be blocking your output. **** (And for completeness, if you had low output with LOW current the 20/30M BPF would be the most likely cause. When it is bad the drive is limited to the PA's, reducing power AND current.) In both cases the problem is usually poorly tinned toroid leads (PTTL). Occasionally we see swapped caps, solder shorts or poor solder connections. 73, Eric ================== Randy Rathbun wrote: > I went ahead and yanked T2 and rewound it. It is honestly the best looking > toroid I have ever wrapped! Don also mentioned some other things to look at > - diode directions, solder joints. Alas, it did not solve the low output. > It did not make things worse, either. Things stayed just the same. After I > noticed that I had one of those "a-ha!" moments. > > I tried 80. Got output. Same with 10, 12, 15, 17. Then I switched to 20. No > output and got the HiCur message and the rig showed 0.1 out. Same with 30. > > So, now it looks like something is shorted in the 30/20 section. ++++++++++++++++++++++++++++++++++++++++++++++ Date: Fri, 6 Apr 2001 10:06:26 -0700 (PDT) From: agtaylor at llnl.gov Subject: [Elecraft] Re: No 30/20 output on K2 #1981 You might try replacing the 4.7pF cap couling the two tuned circuits in the 20/30m bandpass filter. It was bad, causing low output for me when I built S/N 157. Also, Bob N7XJ reportedly had the same problem with his FT unit S/N 0013. Those little caps are amazingly fragile. Let me know if it helps. Allan K7GT - -- Allan G Taylor agtaylor at llnl.gov ++++++++++++++++++++++++++++++++++++++++++++++++ Date: Mon, 9 Apr 2001 15:43:36 -0700 From: "Randy Heise" Subject: Re: [Elecraft] No 30/20 output on K2 #1981 Hi Luigi: Can't speak for T2, but it sure did seem to matter on T5! Gary lead me thru that whole section and I still had no oscillation from the VFO. I finally realized that I had 'inverted' the secondary .... i.e. if you look at fig 6-16 on page 51 of the manual (rev c) my secondary winding went underneath at 3 and out the top at 4. Pulled it out, re-wound the secondary as shown and everything was fine. Could it have been a bad solder job? Maybe.... but I had reheated those pads 4 times. Doesn't seem like from the circut that it should have made a difference, but it sure seemed to! So who knows?? Randy AA6XM - ----- Original Message ----- From: To: Sent: Saturday, April 07, 2001 10:29 AM Subject: Re: [Elecraft] No 30/20 output on K2 #1981 Hi Eric, One question on T2 that has come up a number of times... Does it matter in which direction the secondary is wound? Luigi W7DZN +++++++++++++++++++++++++++++++++++++++++++++++++++++ Date: Mon, 9 Apr 2001 19:52:14 EDT From: LHLOUSEK at aol.com Subject: Re: [Elecraft] No 30/20 output on K2 #1981 Hi Randy, <<>> The dots on the schematic for T5 (near lead 2 and 4) are there to indicate=20 that phasing of the windings is important. =A0Note that on T2 there are no d= ots=20 but there are dots on T3. =A0According to the notation then, it is important= =20 for T3, T5 and T6 but not the others. =A0 Also, from analyzing the schematic for the VFO you can see that the leads 2=20 and 4 of T5 for example, are AC coupled to the same portion of circuitry=20 (Q18) so their relative phases would be important. =A0That is not the case f= or=20 T2. =A0People have wound T2 both ways and have not noted any difference in=20 power or operation of the unit.=20 The diagram for winding T2 is ambiguous so I would like verification of the=20 correct way to wind T2, if there is a correct way, or to say it doesn't=20 matter if it makes no difference. =A0Looking carefully at the photos in the=20 manual it appears to me that T5 is wound in a way that is different from=20 either way that I can interpret the diagram. Lou =A0W7DZN +++++++++++++++++++++++++++++++++++++++++++++++++ Date: Fri, 13 Jul 2001 21:44:19 -0400 From: Michael Ardovino Subject: [Elecraft] 20m Low Power + Quirks Hello Fellow K2 Builders, I ran into a snag during transmitter alignment of my K2 #2118. I cannot get more than 2.7w out on 20m. All the other bands check out ok with at least 10w rf. My readings using K2 internal wattmeter into a 50ohm dummy load are: 14000khz 2.6w 14100khz 2.7w 14200khz 2.3w 14300khz 1.7w 14350khz 1.3w I have tried adjusting L8, L9, C21, & C23 several times and the 2.7w is maximum (13.3v, 1.38a). I have verified correct parts placement and reheated all pertinent solder connections in the 20/30m BPF and LPF. There is also a quirk I discovered when checking xmtr output levels. ONLY after transmitting on 20m first[using TUNE], then switching to either the 30m or 17m band with the POWER set to 5w, the power out jumps to 15w on 30m and 17m. Switching back to receive, then TUNE a second time without changing bands or power setting from 5w, while on 30m or 17m will output 5w. Transmitting via the keyer results in a slight variation of the above scenario. The power jumps to 15w on 30m/17m but stays at that level until the band is changed. I may have more than one problem here and could use some help, any suggestions? Mike - N2EAB miketa at worldnet.att.net ++++++++++++++++++++++++++ Date: Sun, 15 Jul 2001 17:49:02 -0400 From: Michael Ardovino Subject: [Elecraft] 20m low power fixed FYI, I resolved my 20m low power problem with the 20 turn technique of C21 and C23 as suggested on the builders resource page. I missed seeing that info the first time I looked. Both 20m Band Pass Filter trimmers are very "touchy", the initial settings of mid-position didn't yield any power out and the final settings are nearly at maximum capacitance for both. The proper tuning of this BPF also appears to have removed the quirks(power jumps on 17m and 30m) I had experienced. I am extremely pleased with how well the kit is designed and am enjoying building it. Thanks Eric and Wayne. Now on to some contacts and then the options :) Mike - N2EAB K2 #2118 +++++++++++++++++++++++++++++