VCO Oscillator Problems and T5
Posted by
Gottlieb, Jonathan on
Apr 25, 2005; 7:18pm
URL: http://elecraft.85.s1.nabble.com/VCO-Oscillator-Problems-and-T5-tp377563.html
I recently posted a note regarding the fact that I was stuck on the VCO Oscillator Test (p.60) of my K2, #4856. Don, W3FPR gave me some good suggestions, but nothing seemed to fix the fact that I couldn't get the oscillator to oscillate. I replaced Q1 and Q2 and the JFET. Still no oscillation. Being an attorney, not an engineer, I figured I better bring in a specialist, so I turned everything over to Andy, WA3LTJ (MSEE and avid builder) to see if he could get things working. After eliminating all other possibilities, Andy looked carefully at T5, which turned out to be the problem. Page 54 of the manual tells you that windings 1-2 will look *similar* to Fig. 6-15. Page 55 says that windings 3-4 must be wound *exactly* like Fig. 6-16. Being an attorney, I read the manual carefully. I wound 1-2 *similar* to the picture and 3-4 *exactly* like the picture. Note the difference between *similar* and *exactly*.
Here is where I went wrong: my T5 windings 1-2 were in the opposite direction as winding 3-4. If the directions of the two sets of windings are not the same, then the T5 connections are out of phase and the Oscillator will not oscillate. After rewinding T5 so that both 1-2 and 3-4 are exactly as pictured in Fig. 6-16, everything is working great. Am I the only one who has had this problem? (Maybe I'm the only lawyer who has tried to build a K2). I think Elecraft should include an errata that says *both* windings of T5 must be look exactly as pictured, or at least make sure the windings start and end in the same directions.
Jonathan Gottlieb
WA3WDK
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