[Swan] 500-CX Tech Assist Needed

Sat, 28 Feb 2004 21:16:51 -0600

Try tightening all screws  holding things down to the chassis.  Maybe you
have a poor ground connection due to a loose screw.
Lee, w0vt
Houston
----- Original Message ----- 
From: "Dan Hatcher" <[email protected]>
To: <[email protected]>
Sent: Saturday, February 28, 2004 4:56 PM
Subject: [Swan] 500-CX Tech Assist Needed


> Folks:
> Hopefully, someone can provide help to solve a most unusual problem I'm
> having w/ a really nice 500-CX.  Radio had been working fine and then
> .........
> In receive, on 80 & 40 M, it breaks into an oscillation when I adjust the
> P.A. GRID control.  On 80 M, any position of the PA GRID will cause a
raspy
> oscillation but it will peak at a certain setting; on 40M, the
oscillations
> occur over a narrow range of PA GRID control movement.    20/15/10 M seem
> normal.
>
> Problem seems independent of dial frequency or any other control - loading
> (coarse/fine) has no effect on the oscillation.
>
> I've not read any problem like this in the Swan Compendium or Newsletters.
>
> I've checked the receive RF amp (6BZ6, in this variation of 500-CX) &
mixer
> (12BE6) tubes  & the xmit driver (and swapped them out w/ known good ones
> also).  I've cleaned the 500-CX power connector pins,  tried 2 other power
> supplies, measured the various voltages (seems within tolerance) & even
> resoldered all tube socket pins on the rec amp/mixer - all w/o success.
>
> It appears as though some feedback path exists in the mixer area - I can
> duplicate the effect w/ the rec amp tube removed, which doesn't make much
> sense at all, since the PA GRID control effects the receive signal path as
> applied to the rec RF amp.
>
> I would appreciate any insight you Swan lovers might have - maybe I'm to
> close to the problem & am overlooking the "obvious".
>
> 73 & thanks in advance
> Dan KD3CQ
>
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