{"id":6860,"date":"2013-03-27T12:49:11","date_gmt":"2013-03-27T19:49:11","guid":{"rendered":"http:\/\/rustybolt.info\/wordpress\/?p=6860"},"modified":"2013-04-01T08:26:50","modified_gmt":"2013-04-01T15:26:50","slug":"2013-03-28-tbd","status":"publish","type":"post","link":"https:\/\/rustybolt.info\/wordpress\/?p=6860","title":{"rendered":"2013-03-28 Built Several Germanium Joule Thiefs"},"content":{"rendered":"

\"\"<\/a>I went on a Joule Thief building binge for a few hours last night, making up some germanium Joule Thiefs after I found a small box of old unidentified germanium transistors that I had forgotten about.\u00a0 I used a small piece of the “Woodsies Squares”<\/a> thin birch plywood about 1\/2″ by 1″ (12.5 by 25 mm) that I got from the crafts store.\u00a0 I used the #60 wire size drill in a General #92 pin vise to drill the holes to mount the parts.\u00a0 The PNP germanium transistors had barely visible remnants of labels on the top; might have been Texas Instruments symbols.<\/p>\n

I got some of these transistors in a lot I bid on on eBay, for a very low price if I didn’t count the shipping (the seller, apparently not knowing what they were, called them resistors).\u00a0 The transistors are apparently from the first decade of the transistor, probably late fifties to early ’60s.\u00a0 They measured low gain, so I used a lower value resistor, 390 ohms for one JT, 470 and 560 ohms for the others.\u00a0 I haven’t completely assembled the third one, which will probably have another 470 ohm resistor.\u00a0 I had several germanium JTs working, but none were neatly assembled on a board, they were just tack soldered together.<\/p>\n

I used T231212T cores from Surplussales.com, with three conductors of 30 AWG solid enameled wire, about 6-1\/2″ (17cm) long wound trifilar.\u00a0 I paralleled two of the three to make the primary and the remaining single winding became the feedback winding.\u00a0 What really has me puzzled is why I had such a large discrepancy in the three coils I wound.\u00a0 All three cores were pulled from the same bag.\u00a0 I wound all three coils identical, with about 6-1\/2 inches of the same 30 AWG wire, trifilar.\u00a0 They all had about the same number of turns.\u00a0 Two of the coils measured 105 to 115 microhenrys, while the third measured 440 uH, almost four times higher.\u00a0 My thoughts were that the seller had dumped more than one type of core into the same bag and mixed them up, so that they were actually selling two (or more) different cores as the same part number.\u00a0 Or another theory might be that the manufacturer was selling this as floor sweepings or rejects, and the seller was hiding the fact that the parts were not new.\u00a0 Whatever the case, I may have to go through the whole bag of them and test each one, because I have several dozen still left in the bag.<\/p>\n

This morning, Mar 29, I dumped a bunch of the cores out and started measuring each one by slipping a short length of resistor lead in the clips of the LC meter through each core.\u00a0 This single turn measurement showed about 2 to 2.5 uH for most of the cores, but there was a pile of 20 or more that were ‘substandard’, many measured below 2 uH, some between 1 and 1.8 uH.\u00a0 Those were definitely out of tolerance so I bagged them separately and labeled them rejects.\u00a0 They’re okay for a Joule Thief, they just have lower inductance, that’s all.\u00a0 But still the seller gave the specs and these rejects clearly don’t meet them.<\/p>\n

In the picture the second from the left LED is glowing dimly, and the far right green LED is lit up brightly.\u00a0 This is connected to a Rayovac ‘Heavy Duty’ C cell that was purchased almost 25 years ago.\u00a0 Before I put it on the JT, it measured 1.52 V, less than when it was when new, but still good for lighting up the JT’s LED.<\/p>\n","protected":false},"excerpt":{"rendered":"

I went on a Joule Thief building binge for a few hours last night, making up some germanium Joule Thiefs after I found a small box of old unidentified germanium transistors that I had forgotten about.\u00a0 I used a small piece of the “Woodsies Squares” thin birch plywood about 1\/2″ by 1″ (12.5 by 25 <\/p>\n

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