"Joe" wrote in message
...
Thanks for the tip, Richard. I will look for this issue
next time my
R-388 has its turn at the main listening position.

73,
Joe

It was interesting that the problem turned out to be so
simple after some tail chasing.
I've checked the meter performance since replacing the
resistor. The R-388 meter does not have an absolute
reference, rather it indicates the level above the AVC
threshold. The handbook states this as being about 3 uV on
all bands except No.1 where it is higher. I think this
probably varies somewhat with the particular tubes in the
set and also probably from band to band. On my test, made at
about 4 mhz and checked at about 10 mhz, I found the
threshold to be about 2.5uV
On my receiver the scale is fairly linear up to about
60db and above that is compressed but the meter will go off
scale with enough input. The saturation point seems to be
about 300 to 500 milivolts on bands higher than No.1. Didn't
check it there.
I found that there is a rough correspondence between the
audio decibel scale and S-units assuming S-9 = 50uv
0 RF = about S-4.5
Audio scale
S-7 = -1db
S-8 = -4db
S-9 = -2db
S-9+10db = 0db
S-9+20 = +2db
S-9+30 = +3db
S-9+40 = +4db

At least gives you a sort of reference since S units are
not very exact anyway. Note that the audio level scale is
not co-incident with the RF scale so the level differences
in db don't match. The numbers are simply easier to spot
than those on the RF scale plus the audio scale is uppermost
for some reason.




--
Richard Knoppow
Los Angeles
WB6KBL