{"id":4718,"date":"2011-11-17T22:52:00","date_gmt":"2011-11-17T11:52:00","guid":{"rendered":"https:\/\/www.homebrewradio.us\/blog\/2011\/11\/17\/amplifier-woes-help-me-help-me\/"},"modified":"2011-11-17T22:52:00","modified_gmt":"2011-11-17T11:52:00","slug":"amplifier-woes-help-me-help-me","status":"publish","type":"post","link":"https:\/\/www.homebrewradio.us\/blog\/2011\/11\/17\/amplifier-woes-help-me-help-me\/","title":{"rendered":"Amplifier Woes &#8212; Help me! Help me!"},"content":{"rendered":"<p><span style=\"font-size:130%;\"><span style=\"font-weight: bold;\">When I look in the mirror and I see a haunted, obsessed look in my eyes. My wife senses that there is something wrong in the ham shack. She is right. I have an amplifier that wants to be an oscillator. Help me exorcise these gremlins! <\/span><\/span><span style=\"font-size:130%;\"><span style=\"font-weight: bold;\">Guys, this problem is holding up the production of the next SolderSmoke podcast. <\/span><\/span><span style=\"font-size:130%;\"><span style=\"font-weight: bold;\"><\/span><br \/><span style=\"font-weight: bold;\"> <\/span><br \/><span style=\"font-weight: bold;\">My <\/span><a style=\"font-weight: bold;\" href=\"http:\/\/www.phonestack.com\/farhan\/jbot.html\">JBOT amp <\/a><span style=\"font-weight: bold;\">works fine into a dummy load, but when I connect it to an antenna, it gets unstable. Here are some more details of the symptoms: <\/span><\/p>\n<p><span style=\"font-weight: bold;\"> I am running the JBOT with a 5 element (two toroids, 3 caps) <\/span><span style=\"border-bottom: 2px dotted rgb(54, 99, 136); cursor: pointer; font-weight: bold;\" class=\"yshortcuts\" id=\"lw_1321570540_0\">low pass<\/span><span style=\"font-weight: bold;\"> filter (designed by Doug DeMaw and approved by Steve Smith). <\/span><\/p>\n<p><span style=\"font-weight: bold;\"> With the antenna connected, all is well UNTIL I raise the power out (by varying the input) beyond about 1 watt. Below one watt, the amp is working fine, and it stable. As soon as I hit the 1 watt point, the amplifier seems to break into oscillation. This does not happen into the dummy load. <\/span><\/p>\n<p><span style=\"font-weight: bold;\"> The antenna is a simple dipole fed by coax. It shows a low SWR. Even when I put an antenna tuner between the amp and the antenna and bring the SWR down to negligible levels, the instability problem persists. <\/span><\/p>\n<p><span style=\"font-weight: bold;\"> With the amp disconnected from all other circuitry other than the antenna and the power supply, if I just touch the input capacitor, it breaks into oscillation. This does not happen when the amp is working into the dummy load. <\/span><\/p>\n<p><span style=\"font-weight: bold;\"> I&#8217;ve bolstered the power supply filtering and decoupling. No luck. I tried some de-Qing of the transformers. No luck. <\/span><\/p>\n<p><span style=\"font-weight: bold;\"> Any suggestions? <\/span><\/span> <\/p>\n<p>Our book: &#8220;SolderSmoke &#8212; Global Adventures in Wireless Electronics&#8221;<a href=\"http:\/\/soldersmoke.com\/book.htm\">http:\/\/soldersmoke.com\/book.htm<\/a>Our coffee mugs, T-Shirts, bumper stickers: <a href=\"http:\/\/www.cafepress.com\/SolderSmoke\">http:\/\/www.cafepress.com\/SolderSmoke<\/a>Our Book Store: <a href=\"http:\/\/astore.amazon.com\/contracross-20\">http:\/\/astore.amazon.com\/contracross-20<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"<p>When I look in the mirror and I see a haunted, obsessed look in my eyes. My wife senses that there is something wrong in the ham shack. She is right. I have an amplifier that wants to be an oscillator. Help me exorcise these gremlins! Guys, this problem is holding up the production of &hellip; <a href=\"https:\/\/www.homebrewradio.us\/blog\/2011\/11\/17\/amplifier-woes-help-me-help-me\/\" class=\"more-link\">Continue reading<span class=\"screen-reader-text\"> &#8220;Amplifier Woes &#8212; Help me! Help me!&#8221;<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[84,66,68,235,25],"tags":[],"class_list":["post-4718","post","type-post","status-publish","format-standard","hentry","category-amplifier-theory","category-farhan","category-india","category-jbot","category-troubleshooting"],"_links":{"self":[{"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/posts\/4718","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/comments?post=4718"}],"version-history":[{"count":0,"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/posts\/4718\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/media?parent=4718"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/categories?post=4718"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/tags?post=4718"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}