{"id":872,"date":"2012-01-21T08:17:59","date_gmt":"2012-01-21T16:17:59","guid":{"rendered":"http:\/\/rustybolt.info\/wordpress\/?p=872"},"modified":"2012-03-14T18:54:47","modified_gmt":"2012-03-15T01:54:47","slug":"2012-01-21","status":"publish","type":"post","link":"https:\/\/rustybolt.info\/wordpress\/?p=872","title":{"rendered":"2012-01-21 Power Transformer for Line Operated Tube Equipment"},"content":{"rendered":"

I see a number of good designs for vacuum tube (thermionic valve) regenerative receivers in the Yahoo group Regenrx<\/a>.\u00a0 Tubes are hard to obtain and notoriously inefficient; reasons why they would be my last choice for a receiver.\u00a0 But one area they have a big advantage is for use in a ham or SWL receiver connected to an antenna.\u00a0 When a solid state receiver is connected to an antenna, it requires a well designed protection circuit to prevent a nearby thunderstorm from damaging the sensitive transistors.\u00a0 A tube receiver is relatively immune from this kind of damage – tubes are very rugged and hard to damage.<\/p>\n

But back to the receivers in the group.\u00a0 One schematic example can be seen here.<\/strong><\/a>\u00a0 It uses the \u00a8All American Five\u00a8 set of tubes with filaments connected in series and connected directly to the AC line.\u00a0 This is commonly known as a Hot Chassis because of the shock and safety hazard of having the AC line voltage directly connected to the chassis.\u00a0 Even the antenna could become a Live Wire if the chassis is hot.<\/p>\n

I assume that the primary reason for using this design is that a power transformer is very expensive, nowadays and in the past.\u00a0 I have seen power transformers selling for hundreds of dollars (US), and one for a 5 tube receiver could cost as much as a hundred dollars.\u00a0 I think few people know that there is an alternative that will give them a source of isolated B+ at a few tens of watts for about twenty dollars.\u00a0 Along with this solution, they also get a source of filament voltage that is isolated from the AC line.\u00a0 First off go to www.frys.com and search for power transformer.\u00a0 You will get a list of a few pages, and there are several choices depending on the voltage and power level you want.\u00a0 I chose this one<\/strong><\/a> because it gives over 30 watts for about 22 dollars. You need to buy two of them.<\/p>\n

The way to connect these is as follows.\u00a0 One of the power transformer primary windings is connected to the AC line, through a switch and fuse of course.\u00a0 The second transformer\u00b4s secondary winding, in this case 18 volts AC, is connected to the first transformer\u00b4s secondary winding.\u00a0 The primary of the second transformer will then have the AC line voltage fully isolated from the AC line or \u00a8mains\u00a8.<\/p>\n

Let\u00b4s say the five tube radio requires 25 watts of AC power.\u00a0 You can connect the power plug directly to output of the above two transformers and run the radio, with no modifications whatsoever, from the fully isolated AC.\u00a0 If the builder wants to put this into his design, there are several other ways to run the receiver, more like one with a conventional power transformer.<\/p>\n

Instead of using the series string filaments, the builder could use one of these transformers to furnish 6.3VAC or 12.6VAC to all of the tube filaments.\u00a0 The two transformers above would then be used to furnish the B+, but since the power needed would be less, a set of smaller transformers could be used.\u00a0 By the way, you don\u00b4t have to use one from Fry\u00b4s; these Philmore transformers and ones like them are available from other electronics dealers, Radio Shack for one (Catalog #: 273-1511).<\/p>\n

I personally would use mostly solid state components for much of the receiver.\u00a0 I would then use a hollow state fire bottle (tube) for the front end that is connected to the antenna.\u00a0 I would get the 45 to 90 volt B+ by adding a voltage multiplier to the output of the power transformer.<\/p>\n

One disadvantage of this arrangement is that it can take up more room on the receiver chassis.\u00a0 One way to reduce this is to fabricate a U shaped strap of metal and use it to mount the second transformer over the top of the first transformer. \u00a0 I’m sure that the builder can come up with even more ideas to keep his tube project isolated from the AC line.<\/p>\n","protected":false},"excerpt":{"rendered":"

I see a number of good designs for vacuum tube (thermionic valve) regenerative receivers in the Yahoo group Regenrx.\u00a0 Tubes are hard to obtain and notoriously inefficient; reasons why they would be my last choice for a receiver.\u00a0 But one area they have a big advantage is for use in a ham or SWL receiver <\/p>\n

(Read More…)<\/a><\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[8,6,7],"tags":[],"class_list":["post-872","post","type-post","status-publish","format-standard","hentry","category-audio","category-electronics","category-radio-frequency"],"_links":{"self":[{"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=\/wp\/v2\/posts\/872","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=872"}],"version-history":[{"count":13,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=\/wp\/v2\/posts\/872\/revisions"}],"predecessor-version":[{"id":1539,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=\/wp\/v2\/posts\/872\/revisions\/1539"}],"wp:attachment":[{"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=872"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=872"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=872"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}