[Elecraft] Q22 post mixer amp problems

Mon May 5 13:23:01 2003

I also found that my K2 had very low gain at first. I could barely hear only a few signals.

Finally, using DC voltage measurements, I found that Q22 wasn't conducting any current. Even though the solder joint on the emitter
lead looked good with a 3x magnifier, it wasn't. After resoldering the emitter, everything worked fine.  Several people have
reported a problem with Q22. I wonder if there might be a film on the leads?

73/ Bob - AG5Q

----- Original Message -----
From: "Wallace, Andy" <[email protected]>
To: "Ken Wagner" <[email protected]>; "Elecraft Reflector" <[email protected]>
Sent: Monday, May 05, 2003 8:14 AM
Subject: [Elecraft] Q22 post mixer amp problems

> -----Original Message-----
> From: Ken Wagner [mailto:[email protected]]
>
> 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
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