[R-390] Low gain 0.5 MC through 7 MC

[Barry Scott]

Sensitivity on the lower 7 bands is significantly lower than on 8 MC and
up.  I can see this very readily with the signal generator as input and,
with the output level remaining the same, switching from any of the first 7
bands to 8 MC or higher shows a significant (approximately double) rise in
the radio's dB meter.  It's also noticeable just listening to stations.

The common factor seems to be V203 (1st mixer) and I suspect that tube
might have low gain (possibly gassy?).  Is that a reasonable thing to start
with?  I don't see how something affecting the AGC would affect all the
paths to V203's grid and so I was thinking the tube itself might be the
problem.

Thanks,
Barry - N4BUQ