[R-390] Microphonic Parts?

[Barry]

Hi Mike,

I looked for "microphonic" and "vibration" in that article and didn't find anything.  Is there a particular section that talks about this?

Thanks,
Barry - N4BUQ


 On Sat 14/04/12 12:37 PM , "MICHAEL TALLENT" mwtallent at comcast.net sent:
> Yes, ceramic capacitors can be microphonic see this for more info--
> http://www.edn.com/contents/images/6430345.pdf
> Mike T  W6MXV
> 
> ----- Original Message ----- 
> From: "Barry" n4buq at knolo
> gy.net>To: r-390 at m
> ailman.qth.net>Sent: Saturday, April 14, 2012 1:25 PM
> Subject: [R-390] Microphonic Parts?
> 
> 
> >I know that tubes can be microphonic.  Is it likely
> for passive components >to be microphonic as well?
> >
> > I have an old Marconi LCR bridge that I'm trying to
> get working correctly > again (it doesn't want to stay NULLed in R mode). 
> Whilst poking around at > the input of the first amplifier (an EF86) with a
> small plastic stick and > looking for bad grounds or solder joints, I noticed
> that a very light > tapping on the components connected to the control
> grid causes quite a lot > of noise at the detector (as observed on the
> scope).>
> > The components that seem to cause the most noise
> are a 1M resistor and a > 470pF cap.  The cap is connected directly to the
> grid and the resistor is > connected on the other end of the cap to
> ground.>
> > I've loosened and retightened the ground points at
> the tube base and > gently pushed on the solder joints but nothing
> seems to produce this noise > like the tapping does.  Tapping the tube itself
> produces a small bit of > noise, but not nearly as much as these
> components.>
> > Is this "normal"?  I tend not to think so, but the
> control grid of the > first amp is a pretty sensitive place to go
> knocking around on so I'm not > sure if this might just be expected
> behavior.>
> > Not directly related to an R390 but I know you guys
> are a great source of > help for things like this.
> >
> > Thanks,
> > Barry - N4BUQ
> >
> >
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