{"id":516,"date":"2016-08-03T19:52:41","date_gmt":"2016-08-03T22:52:41","guid":{"rendered":"http:\/\/va1der.ca\/?p=516"},"modified":"2017-08-28T09:02:32","modified_gmt":"2017-08-28T12:02:32","slug":"face-meet-egg","status":"publish","type":"post","link":"https:\/\/va1der.ca\/index.php\/2016\/08\/03\/face-meet-egg\/","title":{"rendered":"Face, Meet Egg"},"content":{"rendered":"

So, as I wrote in my last post<\/a>, I had taken my Heathkit SB-104A radio offline due to suspected power supply problems.\u00a0 Under load it appeared to be sending AC directly through to the radio.\u00a0 It turns out this wasn’t the case, that a couple of issues are at at work here:<\/p>\n

    \n
  1. The SB-104(A) is prone to sending RF and the modulated audio signal back up the 13.8V rail.\u00a0 This “talkback”, as it’s known, is a well known SB-104A issue and is addressed in several QST articles.<\/li>\n
  2. My “shack” has terrible, terrible, terrible<\/strong> AC noise and it’s obviously leaking into my radio.\u00a0 Which was then getting onto the 13.8V rail through the same mechanism the talkback audio was.<\/li>\n<\/ol>\n

    So, yes – it’s not my power supply after all.\u00a0 What’s particularly embarrassing is how long it took me to figure this out.\u00a0 I didn’t have anything handy on my bench with which to test the power supply under load (except for the radio itself which I wasn’t going to risk), so I pulled the filter capacitors out to test figuring they had to be the culprits.\u00a0 When it looked like they were good, puzzled, I began preparations to test every part of my power supply if need be to determine where the trouble lay.\u00a0 I was even writing a blog post about it – I was going to title it “combat troubleshooting”.\u00a0 My workbench, while increasingly well kitted, is woefully short of those odds and ends parts most old-time hams have which let them whip together pretty much any kind of test circuit they need at a moment’s notice.\u00a0 So I was going to do a bit of “combat troubleshooting” and (as Matt Damon said in a great movie recently) “science the shit” out of my power supply to work out where the problem was with a minimum of equipment.<\/p>\n

    That’s when it occurred to me, it should actually be quite easy to test my power supply under load – I don’t need load resistors, a few automobile headlight bulbs in parallel should be just the trick.\u00a0 And wouldn’t you know it, when I hooked them up to be the load, what did I see but a beautiful, stable, exactly 13.8 volt DC line without even a whisper of ripple.<\/p>\n

    Face, meet egg.<\/p>\n","protected":false},"excerpt":{"rendered":"

    So, as I wrote in my last post, I had taken my Heathkit SB-104A radio offline due to suspected power supply problems.\u00a0 Under load it appeared to be sending AC directly through to the radio.\u00a0 It turns out this wasn’t … Continue reading →<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":[],"categories":[24,25],"tags":[],"_links":{"self":[{"href":"https:\/\/va1der.ca\/index.php\/wp-json\/wp\/v2\/posts\/516"}],"collection":[{"href":"https:\/\/va1der.ca\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/va1der.ca\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/va1der.ca\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/va1der.ca\/index.php\/wp-json\/wp\/v2\/comments?post=516"}],"version-history":[{"count":7,"href":"https:\/\/va1der.ca\/index.php\/wp-json\/wp\/v2\/posts\/516\/revisions"}],"predecessor-version":[{"id":535,"href":"https:\/\/va1der.ca\/index.php\/wp-json\/wp\/v2\/posts\/516\/revisions\/535"}],"wp:attachment":[{"href":"https:\/\/va1der.ca\/index.php\/wp-json\/wp\/v2\/media?parent=516"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/va1der.ca\/index.php\/wp-json\/wp\/v2\/categories?post=516"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/va1der.ca\/index.php\/wp-json\/wp\/v2\/tags?post=516"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}