[R-390] Weak Stage Gain at First Mixer

[Barry Scott]

I've been testing the stage gain per the manual at the first mixer
(R-390/URR).  While I can get -7v at the DIODE LOAD in the 0.5-1mc
range and almost the same in the 1-2mc range, as I approach the 7-8mc
range, the the gain drops off by a few volts and it takes more than a
few microvolts to get to -7v in those ranges.

As a test, I removed Z219, Z220, and Z221 and, making sure the radio
was in one of the lower bands, I injected a signal at pin 3 of Z221.
I increased the SG voltage until there was -7v at the DIODE LOAD and
then moved the injection point to E209.  Essentially, I wanted to see
if there was anything between those two points, specifically C312)
that might be attenuating the signal.  With the injection point at
E209, the voltage amplitude increased at the DIODE LOAD by about 1.5v.

I'm not sure if that's normal but I tend to think it shouldn't have
made that much difference.  Does it sound like this might be pointing
to a problem or should this be considered more-or-less normal?

Thanks (and continuing to grab at straws for this...),
Barry - N4BUQ