Grounding gear
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Hi gang,
I know grounding has been flogged on this Reflector before but I have a question to ask the collective about a problem I have struck. A while ago, I managed to convince an interested party to buy a second hand K2/100 complete with KAT100, that came on the market at a good price. I knew the set as I had built it myself and had every confidence in it, however not long after the new owner took delivery, I received a report that it had gone "bang" and smoke had come out of it, and it wouldn't work anymore on the KPA100. The amplifier was sent up to me and it was found that 2 of the T/R 1N4700 diodes were short-cct...the smoke had been provided by R40 burning out. The amplifier had been previously been bought up to the latest specs, but C64 hadn't been changed to the larger value now specified, so I suspected that must have been the culprit. I replaced the diodes, resistor, Cap,and ZVN4424's (just in case) and tested the amp as OK on anything I had here. The amp was returned and has run for a month or so, until I received notice that it was playing up again. The problem arose on the same antenna as before, which is a 40/20m vertical, that apparently the KAT100 has always had a bit of trouble finding a match on, and once again, when TUNE had been initiated, all the LED's on the ATU lit up and the set locked up.....it was apparently tried a couple of times before the fuse in the 13.8v lead blew. It sounds to me like RF feedback upsetting the rig and causing the amp to oscillate? Now.....in this particular shack, the chap does not ground his gear, but rather uses counterpoises on his long wire ( connected to where I am not sure) and radials on the vertical ( which I presume are above ground as it is a roof mounted vert), but no ground wire connected to the K2/100 or KAT100. Am I right in assuming a "ground" connection on the K2 "may" help? ( Elecraft provide the terminals?)....I would have imagined the set shouldn't "take off" under any reasonable circumstances, but when RF feedback (as I suspect) comes into the equation anything can happen. Any ideas?? Regards.....Ron ZL1TW _______________________________________________ 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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Hi Don,
You are absolutely right about it being C31 that required the change, and that indeed was the one that I did change . I made the mistake in my note by looking at the circuit I have all the mods shown on and picked the wrong one to mention.....DUH. Thanks for picking that one up... Cheers....Ron ZL1TW ----- Original Message ----- From: "Don Wilhelm" <[hidden email]> To: "Ron" <[hidden email]> Sent: Tuesday, September 11, 2007 7:15 AM Subject: Re: [Elecraft] Grounding gear > Ron, > > It is C31 that must be increased to .2 uf or larger (.22 uf is the proper > value), not C46 as you stated. > Was that a typo or is that a possible cause of the problem? > > I do not think grounding the K2 will help. Yes, without the change to C31 > the amp can oscillate - at about 660 Hz. Look at the path through the new > inductors (15 uHy) and series capacitors (4700 pf) through the T/R switch > and you will see that, save for C31 acting as a bypass, there is a nice > series resonant path from output to input, and it is resonant at about 660 > Hz. C31 must be increased to act as a good bypass at the 660 Hz > frequency. > > 73, > Don W3FPR > > Ron wrote: >> Hi gang, >> I know grounding has been flogged on this Reflector before >> but I have a question to ask the collective about a problem I have >> struck. >> A while ago, I managed to convince an interested party to buy a second >> hand K2/100 complete with KAT100, that came on the market at a good >> price. I knew the set as I had built it myself and had every confidence >> in it, however not long after the new owner took delivery, I received a >> report that it had gone "bang" and smoke had come out of it, and it >> wouldn't work anymore on the KPA100. The amplifier was sent up to me and >> it was found that 2 of the T/R 1N4700 diodes were short-cct...the smoke >> had been provided by R40 burning out. >> The amplifier had been previously been bought up to the latest specs, but >> C64 hadn't been changed to the larger value now specified, so I suspected >> that must have been the culprit. I replaced the diodes, resistor, Cap,and >> ZVN4424's (just in case) and tested the amp as OK on anything I had here. >> The amp was returned and has run for a month or so, until I received >> notice that it was playing up again. >> The problem arose on the same antenna as before, which is a 40/20m >> vertical, that apparently the KAT100 has always had a bit of trouble >> finding a match on, and once again, when TUNE had been initiated, all the >> LED's on the ATU lit up and the set locked up.....it was apparently tried >> a couple of times before the fuse in the 13.8v lead blew. It sounds to me >> like RF feedback upsetting the rig and causing the amp to oscillate? >> Now.....in this particular shack, the chap does not ground his gear, but >> rather uses counterpoises on his long wire ( connected to where I am not >> sure) and radials on the vertical ( which I presume are above ground as >> it is a roof mounted vert), but no ground wire connected to the K2/100 or >> KAT100. >> Am I right in assuming a "ground" connection on the K2 "may" help? ( >> Elecraft provide the terminals?)....I would have imagined the set >> shouldn't "take off" under any reasonable circumstances, but when RF >> feedback (as I suspect) comes into the equation anything can happen. >> Any ideas?? >> Regards.....Ron ZL1TW >> >> >> _______________________________________________ >> 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 >> >> > > > -- > No virus found in this incoming message. > Checked by AVG Free Edition. Version: 7.5.485 / Virus Database: > 269.13.12/997 - Release Date: 9/09/2007 10:17 a.m. > > _______________________________________________ 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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