The lamp will glow when you have bias current flowing. So not a problem.
Just remember to make sure the adjustment is still correct when on full mains as it can change with the higher supply voltage.
The centre pin of the resistor pack will go to the speaker output and so measuring from speaker + to that centre pin would always show as 0 volt. If the manual says to do it that way then it is wrong. You have to measure across one of the resistors which you seem to be doing.
8mv will about 36 milliamps current
A buzz a loud buzz, a quiet buzz. It needs quantifying and checking. Does it change with the volume control for example.
If the resistor is in series with a relay coil, sitting there running hot day in and day out, it could turn brown into violet easily. Discoloration is a sign of long term (over)heating. And if it does read 490 ohms that pretty much confirms that it’s running too hot - values tend to go *up*. Probably using 1/2 watt carbon film when they really needed 2 watt MOX or WW for long term stability.
mmm i will,eventualy, trouble is i have 17 nads yet to fix
oh by the way the buzz dissapeared with those 10 loose joints
sorry yes composite