[Elecraft] deaf receiver...

[John Webster]

Hi Andy and others on the list:

Thank you for your very informative post.

I have just completed construction on my K2
to the point of Alignment and Test part II.

All has gone extremely well so far. However,
I have a deaf receiver.  There seems to be
two problems:  low RF sensitivity, and low
audio.  The latter problem is clear: good
sounding signals but very soft.  I have to run
the audio gain full open to hear at comfortable
levels in my headphones (I've tried several).
I know there has been much discussion on
this issue but any quick pointers to start my
quest would be much appreciated.

The other problem brings me back to Andy's
post.  Just by chance I happened to put my
finger on the body of Q21 (the RF Preamp
a 2N5109--the same transistor as Q22
which Andy talks about) and the signal level
shot up remarkably.  I mean from nothing on
the S-meter, to S9 plus 20 etc.  Audio still
soft, but clearly good signal reception is going
on.  What gives here?

Could this be a similar problem to that which
Andy found with Q22 (residue on the leads)?
Or does it indicate some other problem and
my finger just acts as a bypass route around
the real problem?

Any help would be greatly appreciated.

PS.  Even with the two above mentioned
problems, I can clearly hear the superiority
of the K2 receiver on 40m compared to my
Kenwood TS-850 (not a bad RX in its own
right!).  The signal on the 850 sounds NOISY
full of junk, almost difficult to copy, while on
the K2 it is clear and perfectly readable.  In
fact I'm quite blown away by the difference.

Now to get these problems solved . . .

73

John, N6JW

----- Original Message -----
From: Wallace, Andy <awallace@mc.com>
To: Nate Lewis <nlewis59@attbi.com>; Elecraft Mailing List
<elecraft@mailman.qth.net>
Sent: Friday, July 11, 2003 4:32 AM
Subject: RE: [Elecraft] deaf receiver...


> -----Original Message-----
> From: Nate Lewis [mailto:nlewis59@attbi.com]
>
> I've got a mostly-deaf K2 that seems to think that all signal
> or noise is S3 at best, on all bands, and puts out very quiet audio.

Hi, Nate. My K2 also had very low sensitivity. I checked many things
"by the book" and was still scratching my head. One thing which would
really be an improvement to the K2 documentation would be some
oscilloscope snapshots at important stages in the rx, with a known
signal injected at the antenna jack. The difficulty I found was
that using a signal generator in the troubleshooting section and
looking at the voltage levels using the Elecraft RF probe, I didn't
see much that was off the listed values.

Since I assembled my kit using a binocular microscope, I was pretty
sure it wasn't a workmanship issue. However, since the problem seemed
to be in the post mixer amp area, I resoldered Q22, RFC11 (on its
collector) and C161 (the IF coupling cap out of Q22). This seemed
to fix it. Unfortunately, I shotgunned all three at once so I don't
know which it was! All three had solder joints that looked perfect.

I wound up rewinding and reinstalling the RFC and replacing the cap
anyway, just in case.

My suspicion is that Q22 was not soldered well, and from talk on the
Reflector afterwards, my thought is that perhaps Elecraft has a
batch of those transistors which may have residue on the leads. I don't
have the message handy but I believe someone else saw that.
No way to verify though it may be worth Scott taking a look in the stock
and checking. Or they may have already been used up...

Anyway, I'd check that area. I'm cc'ing the list in case anyone else
has had trouble around Q22 and can speak up.

My K2, before the fix, took over 350 uV in the antenna jack at 7 MHz for an
S-9 reading. Now, it is 110 uV or less, and the other bands match
pretty well what the QST review quoted (see the Elecraft site
for the review).

Andy

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