This circuit has three possible conditions. Where the cap is unconnected, or switchable to either live or common wires in the event that incorrect polarity is applied to power the amp. So logic dictates that if the cap can be switched out it was never intended as a safety device.

Some famous products simply connected the circuitry directly to the mains and caused many a shock and death. But the Gibson has incorporated wiser circuitry.

The first point at which safety is introduced is with the fuse, which will blow if it senses current beyond its designed use. This will work in both polarities.

The ac works at 60hz, a resonant frequency that can become a dominant sound in the amplifier. So the cap helped reduce its presence. Canny engineering can achieve a marked improvement.

Also the cap is not a stand alone thing. The cap and the transformer form a circuit. Its ability to filter is integral to the value of the coil in the transformer, which is acting as an inductor. So it is an LC filter.

It would need a lot more maths and physics to understand more about it, and I didn't achieve the headpiece for that.

But if its a fundamental thing to the balance of the whole system, it would need to be retained.

Using: Dell 3268 i3, 8 GB ram, windows 10. Biab version 2017 standard package, no extras.