[R-390] Re:Latest R390A Project

[n4buq at knology.net]

On Tue, 17 Oct 2006 16:39:45 -0400, "Drew Papanek" 
<drewmaster813 at hotmail.com> wrote :

> 
> Barry wrote (snipped for brevity):
> 
> >Switching to SLOW causes the IF voltages to increase substantially 
(maybe a 
> >factor of 3 or 4 times that of MED or FAST).  It seems to distort just a 
> >little on SLOW mode as well, particularly on strong BC stations.
> 
> The classical cause of that problem is leakage in the 2uF chassis-mounted 
> AGC
> integrator capacitor.  I experienced that problem; replacement with an 
> under-chassis
> mounted new film type cap cured it (left old disconnected cap in place on 
> chassis
> for appearance sake).
> 
> >I then watched the AGC voltages last night.  All three postitions yield 
> >very close to the same value (about -2.5V if I recall correctly).
> 
> How close is "very close"?  Because of the large number of gain-
controlled 
> stages
> in the R-390A, a small change in AGC voltage has a relatively large 
effect 
> on gain.
> It doesn't take much leakage to drag the AGC voltage down just a smidge 
> thereby
> causing the problem you report.
> 
> Drew

Probably less than 0.2V.  I figured a badly leaking cap would have made a 
greater change than that but maybe not.  I plan to replace it.

Thanks,

Barry - N4BUQ