[AMRadio] Screen bypass caps (was DX-100B on Phone - bad audio distortion /oscillation)

[wb3fau at att.net]

You  have to understand Heath, Rick.  They   got deals on surplus parts.
 OK  on the screen bypass  caps, again surplus deal  on  parts.  0.001 would  be fine.   The  micas  as you say,  may not actually be mica.   There  were some called micamold,  these  were  molded paper.  Keep inthe back of your mind,  " this is 50+ years old".  1625 modulator tubes- 
military surplus...Russ.

--- On Thu, 12/15/11, Rick Poole <wa1rkt at arrl.net> wrote:

> From: Rick Poole <wa1rkt at arrl.net>
> Subject: [AMRadio] Screen bypass caps (was DX-100B on Phone - bad audio distortion /oscillation)
> To: amradio at mailman.qth.net
> Date: Thursday, December 15, 2011, 8:38 PM
> 
> Any particular reason those 0.0013-uf screen bypass caps in
> the 
> DX-100 finals aren't something more common like
> 0.001?  I mean, it's 
> not like they have to resonate with anything.
> 
> Oh, by the way, all you guys that told me to replace the
> screen 
> bypass caps... just discovered that one of the screen
> bypass caps 
> wasn't even soldered on the ground end.  It looks like
> it has been 
> like that since the day it was first assembled, 50+ years
> ago.
> 
> I am closing in on the problem.  I backed out of the
> SB-10 mod and 
> now when I put my scope probe on the wire running from the
> output of 
> the driver to the grids of the finals, the problem seems to
> go 
> away.  There's a 47-pf mica cap between the grids and
> ground and I am 
> replacing that.  But, I thought micas were supposed to
> be safe from 
> "old capacitor disease".
> 
> Rick WA1RKT
> 
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