VCO Oscillator Problems and T5

[Gottlieb, Jonathan]

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
_______________________________________________
Elecraft mailing list
Post to: [hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
 http://mailman.qth.net/mailman/listinfo/elecraft   

Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com

[Mark J. Schreiner]

One of my fellow local hams is also building a K2 now.  He got his before I ordered mine after we had discussed this for some time.  I'm glad he ordered his first, because it was the kick in the butt that I needed to order mine!  Anyway, I got off the ground running with assembling mine first, although he wasn't too far behind.  When he got to the point where he started winding the torroids (and I was already done with mine) he asked me if it seemed to me like they were all being wound "backwards".  Well, for any of the inductors that are just inductors it doesn't matter as there isn't any phase relationship to this, just one "goesinto" and one "goesouta" lead.  I guess he wound his backwards and crossed over the leads to fit into the hole pattern on the board.  I did warn him to make sure that if he winds them backwards to do so consistently when winding the transformers for the exact reason that Jonathon found out!

Also, even with winding "exactly" and "similarly" I still had to tweak the spacing of the windings slightly on T5 (I think it was) to get the upper and lower band edge voltages set correctly during one of the alignment steps.

Glad you (and your MSEE friend) got it figured out!

Mark, NK8Q
K2 4786

>From: "Gottlieb, Jonathan" <[hidden email]>

>Subject: [Elecraft] VCO Oscillator Problems and T5


>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?

_______________________________________________
Elecraft mailing list
Post to: [hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
 http://mailman.qth.net/mailman/listinfo/elecraft   

Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com