[Elecraft] K2/100 #4198 PA Stability Problem?

Wed May 5 03:33:00 2004

RFC10 was actually on top of the socket rather than beneath it, but I've
moved it and no change. Yes - the box has the shield kit with clips (and
I did sand the side panels!), although in and out of the box and shield
on / off makes no odds. The oscillation is actually quite stable -
moving hands - screwdrivers around makes almost no difference. I said
that the LF frequency increases slightly with frequency - I meant power!
And it seems to get less as the PA warms up. PA or ALC I wonder?
=20
Andy

	-----Original Message-----
	From: Don Brown [mailto:[email protected]]=20
	Sent: 05 May 2004 03:20
	To: [email protected]; Andy
Cook, G4PIQ
	Subject: Re: [Elecraft] K2/100 #4198 PA Stability Problem?
=09
=09
	Hi
	=20
	Did you mount RFC10 down as close to the circuit board as
possible and against the back panel. It should be setting on the diodes
on the board. Also does the KPA100 have the shield mod that adds the
ground clips if not you need to add the new shield and the solder lugs
that go from the antenna socket to the shield.
	=20
	Don Brown
	=20
	=20

		----- Original Message -----=20
		From: Andy Cook, G4PIQ <mailto:[email protected]> =20
		To: [email protected]=20
		Sent: Tuesday, May 04, 2004 7:37 PM
		Subject: [Elecraft] K2/100 #4198 PA Stability Problem?

		Was feeling very smug with myself yesterday having
finished the K2/100
		in decent time, but having put it on air in a local
contest last night
		and getting some grim audio reports, I've found that I
have a problem!
		Since adding the PA, above around 40W on 80m (and maybe
just a hint on
		160) I get rough AM on the carrier (spreads a long way -
probably pulsed
		if I looked on a scope) at a few hundred Hz. Exact
frequency rises a
		little with frequency . Sound like LF instability in the
PA. On SSB
		makes the audio quite rough - on CW spreads with these
sidebands.=20
		=20
		Before I go round applying the usual tricks of extra C
and snubbing R
		here and there, any suggestions? Have checked for
obviously bad grounds,
		wrong components, removing shield, increasing R98 on RF
board, extra
		1000uF C from Z1 to ground, but none have a significant
impact. Any
		leads?
		=20
		73,
	=09
		Andy, G4PIQ
	=09
	=09
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