[K2]: Low Transmitter Output

[Les Rabe]

  I've spent the last 4 weeks or so with a problem I noticed in
Alignment and test Part III on page 78 of the manual.  I've been
monitoring some of the posts here which have been very helpful in
keeping me on the right track with the debugging.  My own K2 would only
produce 1/2 watt of output when I tuned L1 and L2.

I finally realized that the current was stopping right at Q6, and after
having spent the last 4 weeks trying to find bad solder joints and
poorly tinned toroid leads I grabbed some courage and pulled Q6 out of
the circuit and tested it.  It was shorted.

My question is this:  What should I test to assure myself that I won't
just burn out the new part?  It is perhaps possible that Q6 was bad all
along or damaged during construction, but it is also possible that
something in the circuit caused the failure.  R50 was also bad.  There
were no sparks, smoke or burning smell anywhere when the rig was turned
on and I haven't found any damage to suggest a major electrical event.

Thanks.

Les
AB9WN
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[Don Wilhelm-4]

  Les,

Your implication that an active device failure is a rare occurrence is
correct.
Is your Q6 a 2N5739 or a 2N2166?  If it is a 2N5739, change R46 from the
270 ohms value to 330 ohms to reduce the base current and also the
heating of Q6.

73,
Don W3FPR

On 10/5/2010 8:46 PM, Les Rabe wrote:

>    I've spent the last 4 weeks or so with a problem I noticed in
> Alignment and test Part III on page 78 of the manual.  I've been
> monitoring some of the posts here which have been very helpful in
> keeping me on the right track with the debugging.  My own K2 would only
> produce 1/2 watt of output when I tuned L1 and L2.
>
> I finally realized that the current was stopping right at Q6, and after
> having spent the last 4 weeks trying to find bad solder joints and
> poorly tinned toroid leads I grabbed some courage and pulled Q6 out of
> the circuit and tested it.  It was shorted.
>
> My question is this:  What should I test to assure myself that I won't
> just burn out the new part?  It is perhaps possible that Q6 was bad all
> along or damaged during construction, but it is also possible that
> something in the circuit caused the failure.  R50 was also bad.  There
> were no sparks, smoke or burning smell anywhere when the rig was turned
> on and I haven't found any damage to suggest a major electrical event.
>
> Thanks.
>
> Les
> AB9WN
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>

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