Some H.H. Scott amplifiers and tuners have a Hum Adjustment control that is designed
to minimize 50/60 Hz noise on the tube heaters. The factory adjustment
"...This control is set to minimize hum output and has been adjusted
at the factory for the tubes supplied with the amplifier. When tubes are
replaced or aging occurs, readjustment may be required if noticeable hum develops.
Turn this control carefully until hum is minimized. For the laboratory, use
the following procedure:
A. Turn the (input) level control to zero and put a
resistive load across the output terminal. Connect an oscilloscope in
parallel with the load.
B. Adjust the hum control
for minimum output on the oscilloscope."
You can also perform the Hum adjustment using your hears:
input cables and leave only the speakers connected. On an integrated amp, set
the Input Selector switch to phono and turn up the bass while turning down the
Use the Stereo Selector switch to choose the channel under adjustment, i.e.., LEFT INPUT. Adjust that channel's HUM Adjustment for the faintest hum.
Repeat for RIGHT Channel.