[R-390] {Collins} R390/URR Restoration

[Roy Morgan]

On Jun 1, 2013, at 11:29 AM, Steve Bartz <sbartz at verizon.net> wrote:

> I recently acquired an R-390/URR serial #1961 in reasonably complete condition. ...
> The AGC circuit is not working at all.  In going through the IF deck and testing individual components I found that R554 is a funny shaped 470 ohm molded resistor with round ends and a rough body. All the schematics I have show this to be a 2.2K resistor.  It is in the cathode circuit of the AGC amplifier, V509. 

Here is a scrap of info from a Hollow State News, issue no. 36.  This is about the R-390A, though, so carefully compare component numbers etc.

"There is one anomaly that I discovered. R-554 coming off Z-503 is schematically 2.2K. In four IF decks, the installed
value was 470 ohms (and looked original). I temporarily removed this resistor and used a substitution box to
experiment. It seemed that the 470 sounded much better than the 2.2K or any other value for that matter.
[Metz, Issue #36, pg 5]"

Roy

Roy Morgan
k1lky at earthlink.net
K1LKY Since 1958 - Keep 'em Glowing!