Here's the Kay 703-C with the rear panel removed.

This amplifier has 3 Instrument inputs.  I'm guessing microphone, guitar, and iPod.

Here's the amplifier chassis pulled out of the cabinet.

After using test jumpers to attach a couple good filter capacitors across the old ones, the hum was reduced.

It was apparent that replacing the old caps would at least diminish the hum.

In this photo, you see the old, triple-section filter cap on the right, with its wire leads snipped.

The three blue caps in the center of the photo are the replacements.

Zooming in, you see two small 75 ohm resistors (violet-green-black) soldered across the smallest blue capacitor.

This is the power tube's cathode-bias resistor.  The cap is the AC bypass.

The two 75 ohm, 1/4 watt resistors wired in series replace the original 150 ohm, 1/2 watt resistor which had drifted off value.  The 150 ohm part wasn't readily available.

Here's a portion of the schematic with the four replaced parts circled in blue.

For the full schematic click here:  KAY 703-C SCHEMATIC IN PDF FORMAT.