[Elecraft] Re: Q22 post mixer amp problems

[Ken Wagner]

Hi Andy:
Sure... no problem. The previous K2 was #920 which was before RFC11 became a
do-it-yourself item. It was a small ceramic rf choke. I don't really know
exactly what caused the problem, but R82 and RFC11 went up in smoke. It
happened when I was installing a new KNB using #920 as a test bed. I
probably shorted something that caused Q22 to draw too much current which
caused R82 and the l'il rf choke to fail. The fix was to install a new R82
and wind a new RFC11 using a a FT37-43 and 20 turns of wire. I don't really
think that there is anything wrong with the 2N5109. It is just so easy for a
l'il piece of clipped wire or somesuch to get right where it shouldn't be
and cause something like this.
73, Ken K3IU
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
----- Original Message -----
From: "Wallace, Andy" <awallace@mc.com>
To: "Ken Wagner" <kewagner@ids.net>; "Elecraft Reflector"
<elecraft@mailman.qth.net>
Sent: Monday, May 05, 2003 09:14
Subject: Q22 post mixer amp problems


| > -----Original Message-----
| > From: Ken Wagner [mailto:kewagner@ids.net]
| >
| > I noticed that the gain was  *way* down and
| > that the Rx current draw was now 480ma. It smelled kinda hot as well.
| > Sometimes prior problems are helpful. On an earlier K2, I had
| > a problem with > the Post-mixer Amp circuit and this was
| > producing somewhat the same
| > symptoms, except for the increased current draw.
| > I removed Q22 figuring I would have to replace it.
| > I  checked Q22 with a meter and it seemed OK. I put it
| > back in. Now it works just fine, thank you. I could spend hours
| > speculating what was wrong, but I won't. It works fine now.
|
| I find this _extremely_ interesting - can you tell me what you
| found on the previous rig, as well?
|
| When I built my K2 (#31xx) a few months back, I had problems
| in the exact same area. Resoldering Q22, RFC(16?) and a nearby
| cap brought it to life. (Unfortunately I didn't try one at a time.)
|
| The symptom was that the rig was fairly deaf; no abnormal
| current draw but to get S-9 with the preamp off I had to
| inject about 350 uV at the antenna jack!
|
| After resoldering, measurements very closely matched those in
| the ARRL K2 review. Been fine since. I did rewind the RFC
| and replaced the cap just in case, but left Q22 in.
|
| So this is interesting - wonder if something is up with the
| batch of Q22s in stock?
|
| Andy
|
|