[R-390] Re:Latest R390A Project

[Drew Papanek]

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