{"id":4788,"date":"2019-01-16T19:41:00","date_gmt":"2019-01-16T08:41:00","guid":{"rendered":"https:\/\/www.homebrewradio.us\/blog\/2019\/01\/16\/national-dial-and-gearbox-problem-resolved\/"},"modified":"2025-07-21T17:46:51","modified_gmt":"2025-07-21T07:46:51","slug":"national-dial-and-gearbox-problem-resolved","status":"publish","type":"post","link":"https:\/\/www.homebrewradio.us\/blog\/2019\/01\/16\/national-dial-and-gearbox-problem-resolved\/","title":{"rendered":"National Dial and Gearbox Problem Resolved"},"content":{"rendered":"
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Thanks to all who offered advice and assistance. With help from you guys — and especially from Pete Juliano N6QW — I think I have this fixed.<\/b>

<\/b> Pete was right — the problem was really with the variable capacitor. The one I was using was kind of stiff and irregular in its motion. I found another one in the junk box that was easier to turn (it has one set of ball bearings). This fixed most of the problem.<\/b>

<\/b> I also spent more time making sure the shaft of the cap lined up perfectly with the shaft of the gear box. This also helped a lot.<\/b>

<\/b> I realize now that some of the “stickiness” that I occasionally feel while tuning may be coming from the dial — not from the gear box. It looks like my dial took a hit that slightly bent one portion of it. It seems that the numbers have a bit of trouble clicking over on that portion of the dial. Some lubricant may help there. But I can live with it.<\/b>

<\/b> The receiver now tunes very smoothly and I can go right back to a frequency and find the signal exactly where I left it. There does seem to be a very slight difference depending on whether I “approach from above” or “approach from below” — but this is not a big deal.<\/b>

<\/b> Check out the pictures of the receiver and the VFO. Note the “cardboard from a coat hanger” coil form. The winding is held in place with nail polish varnish. I had planned on having the variable cap, the coil , and the associated fixed caps all in a box for better thermal stability, but the VFO is very stable even without the box. I have the VFO running 455 kc ABOVE the signal frequency. It runs from about 7455 kc to about 7800 kc. I could have set it up to run 455 kc BELOW the signal freq. That would have made it a bit more stable (it is easier to attain VFO stability at lower frequencies) but VFO is so stable that I probably won’t mess with it. I followed DeMaw’s rules: Physical stability, NP0 caps. For the NP0 caps, put several of them in parallel to get the desired capacitance value. Keep heat-producing active components away from the coils and caps. <\/b>

<\/b> Thanks again to Armand WA1UQO for giving me this amazing piece of radio history. And thanks to Tim Sutton for the big box that holds this receiver. <\/b>

<\/b> James Millen knew what he was doing. See: http:\/\/www.isquare.com\/millen\/millen-page.htm<\/a><\/b><\/p>\n

<\/a><\/div>\n","protected":false},"excerpt":{"rendered":"

Thanks to all who offered advice and assistance. With help from you guys — and especially from Pete Juliano N6QW — I think I have this fixed. Pete was right — the problem was really with the variable capacitor. The one I was using was kind of stiff and irregular in its motion. I found … Continue reading “National Dial and Gearbox Problem Resolved”<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":4789,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[42,7,321,41,100,57,53],"tags":[],"class_list":["post-4788","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-40-meters","category-demaw-doug","category-hamel-armand","category-juliano-pete","category-old-radio","category-superhet-receivers","category-vfo"],"_links":{"self":[{"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/posts\/4788","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=4788"}],"version-history":[{"count":1,"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/posts\/4788\/revisions"}],"predecessor-version":[{"id":4791,"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/posts\/4788\/revisions\/4791"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/media\/4789"}],"wp:attachment":[{"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/media?parent=4788"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/categories?post=4788"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/tags?post=4788"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}