I recently aquired an R-388. Its in good condition but
I found the S-meter read very low. From the entries in the
archives of the Collins Collector's List this seems fairly
common. I found that the problem was R-163, a 160ohm
resistor in series with the meter, it had increased in value
to over 200ohms. After replacing it with a good 160ohm film
resistor the meter works normally. There is also a 100 ohm
resistor, r-170, between the meter + side and ground. The
voltage to ground from the screens of two IF stages through
this resistor establishes the reference point for the meter.
I changed this resistor also but the old one checked good.
Evidently this resistor is critical because even though the
difference between the two resistors was only about five
ohms the zero adjustment had to be reset a fair amount.
The meter now goes up to about 95 or higher on maximum
signals and off scale with manual gain.
I am posting this in case it proves of help to someone
else with a similar problem.
FWIW, the meter on the 51J series reads decibels above
the AVC threshold. This is not an absolute level but is
approximately 2.5 microvolts on all but Band-1 (the BC band
where the receiver is delibrately desensitized). This is
different than the meter on the Hammarlund Sp-600-JX, which
reads carrier level and is calibrated in db above and below
one microvolt. When these receivers are working right the
meter is surprizingly accurate.

--
Richard Knoppow
Los Angeles
WB6KBL