[R-390] IF alignment questions and noise issue.

[Roy Morgan]

On Jan 17, 2015, at 10:05 PM, Dennis Wade <sacramento.cyclist at gmail.com> wrote:

> Good evening,...
>        Noise issue:  The RF deck ... now seems to develop a "bacon frying" sound several minutes after a
> cold start.  I've isolated the noise to the RF deck...
>           Any ideas on how I might isolate the noise to a stage in the RF
> deck?

Dennis,

The RF deck has a three test points, labeled E-208, 209, and 210.  If you short these in turn to ground (using a capacitor since at least of them is the mixer grid and has DC bias voltage on it), you will find where the noise is coming from.  Or, you can simply pull the tubes one at a time beginning with the first RF amp.

Most likely you will find that you have a leaky silver mica cap.  Out comes the RF deck for surgery.

Roy

Roy Morgan
RoyMorgan at alum.mit.edu
K1LKY Since 1958