K2 4777 Good news/Bad news and questions

[Mike Monger]

Hi Fellow Elecrafters,

First off I would like to thank all who responded to my questions concerning soldering the lugs/tabs of slug tuned coils.  And, about how long it might take Elecraft to send a replacement for a missing part.  As for the missing part and replacement, it was ten days for me to receive mine, from the day I reported it missing.  It was 4 days before they got it shipped out (since they had gotten behind) and took 6 days to get here (TN from CA).  So, all things considered, not to bad.


Here is my good/bad news report on progress with K2 4777.  Got the missing component today and got it installed, finished with all the resistance checks (all seemed to be in range), VCO voltage checks (none of the voltage checks were less than 1.5 volts or greater than 6 volts).  Setting up filters, alignments etc all seemed to go well.  Thus, I would say that is all good news.  

Now, the bad news.  In the process of doing my first VCO voltage check  my DMM ground probe (I am guessing) fell over from where it was attached to one of the ground points on the RF board and shorted to something.  Since, smoke started to rise.  Upon inspection, I found that R82 (an 18 ohm resistor) to the left of the noise blanker on the schematic and in the 12 volt supply line was burned/blackened.  Needless to say, I was sickened.  But, I continued on with all the tests/alignments.  Since, I could not see how that particular resistor would have any effect on what I was testing/aligning.  And, all was well.

Questions are:

1.  If I recall correctly, BFO frequency range was to be between 9.7/9.8 to some amount higher, I came up with 9.5 or 9.6, is this significant or are we splitting hairs here?

2.  Concerning the smoked resistor,  is it imperative that I replace it with an 18 ohm resistor?  Or, can I opt to replace it with the closest standard value I have on hand (which is either a 15 or 22 ohm)?  I ask this, since I don't know the design criteria.  But, (from what little I know about design) I know that often (when a circuit is designed) the values that are calculated (for a particular component) are often replaced by the closest standard value that is on hand.


Thanks In Advance,

Mike
KT2E
K2 4777

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[Dan Barker]

I don't know enough to be sure, but here's my stab in case noone else chimes
in.

r82/r83 appear to be a voltage divider for q22.

If r82 becomes 22ohm, then r83 ought to go up 122% also.

Another thought, since there's lots of room on that part of the board.

Use 2 of each (15, 22), series/parrallel and make 18.5. Then order right
part and put it in when it shows up.

   +-- 15 --- 22 ---+
---|                |---
   +-- 15 --- 22 ---+

or two 33's or two 4.7's and a 10, or ....... whatever.

Dan / WG4S / K2 #2456


<snip>

2.  Concerning the smoked resistor,  is it imperative that I replace it with
an 18 ohm resistor?  Or, can I opt to replace it with the closest standard
value I have on hand (which is either a 15 or 22 ohm)?  I ask this, since I
don't know the design criteria.  But, (from what little I know about design)
I know that often (when a circuit is designed) the values that are
calculated (for a particular component) are often replaced by the closest
standard value that is on hand.
</snip>

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