The instructions for how to use the hum balance pots was left out of the Stereomour II manual. Manuals dated 09-21-18 or later will have these instructions.
Connect the black lead of the meter to the black binding post of the right channel. Connect the red lead of the meter to the red binding post of the right channel.
To find the lowest possible position on the hum pot, you will also need to connect a speaker to the binding posts
Set the meter to read AC volts. If your meter does not autorange, set it to the lowest AC millivolt (mV) scale. Turn the volume pot all the way down to short the input. This will help keep outside electrical interference from affecting the reading on your meter.
Install all tubes into their respective sockets.
Turn the amplifier on let it warm up for a minute or two. Then slowly adjust the hum balance potentiometer behind to the four pin tube socket to get the lowest reading possible on the meter. This should be between 0.8 and 2.0 mV depending on the tube used.
Repeat this process for the left channel tube.