[Elecraft] Question about K2's Q7 and Q8 Final Amp

[Brian Wruble]

A question on this subject...  I had the same problem, after I installed the
100 watt amp and put everything back together.  I solved it with new pads.
The only symptom was a failure to develop output power.  It was awhile ago.
It may be that the thing refused to power-up at all, I just don't remember.
There was never any smoke, no loss of the finals.  When I loosened the
screws holding Q7 and Q8, everything worked.  After I replaced the pads, I
was able to properly tighten the screws with no problem.

I have assumed there is protective circuitry so that a short to ground would
not blow anything.  Was I just lucky? I don't have the schematics in front
of me, so I can't look to see for myself.  My K2 lives a few states away.

Thanks for any insights.  73 de Brian W3BW 

-----Original Message-----
From: elecraft-bounces at mailman.qth.net
[mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Terry Bassett
Sent: Monday, October 04, 2004 10:39
To: elecraft at mailman.qth.net
Subject: Re: [Elecraft] Question about K2's Q7 and Q8 Final Amp

On Monday 04 October 2004 08:16, redmen1969 at optonline.net wrote:
> Hi,
>
>   My K2 has been working fine but I decided to fix it anyway...hi.
>
  The K2 manual warns that whenever the heat sink is
> removed and replaced you should verify that the collectors of Q7 and Q8
are
> not shorted to ground.
>

> Tom, WB2QDG
> K2 1103

Hello Tom,

	The way I blew one of mine was due to a very tiny fragment of metal
shaving 
getting  installed along with the heat transfer pad of Q7, I took only a
very 
short time to let the smoke out.  
	This happened quite some time back, so I can't remember what I was
doing or 
trying to accomplish, but I'd say if you've done anything to Q7/Q8 and can't

find the short to ground.   It "might" be something like what I did.
Believe 
me it was a tiny, tiny fragment, but when Q7 was tightened down it made 
contact and did its damage.

	Just a bit of my experience that you can check and maybe gain from.

73,

Terry  KA9TXE
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