Vintage preamp/amp power cords

One of my early mods long ago, replaced the factory cord. Only my approach was, long as I got the soldering iron out.... hardwired the new one in.

This was back when I wasn't really even sure it would make a difference. Now I would still recommend hard wire if you have one you know you have heard and know you will be happy to live with. Anything other than that you need to audition several, and that means iec.

Safety, unless you see signs of overheating or fraying or cracking, you can just forget that one except if it helps as an excuse to rationalize what you should be doing for sonics sake. Even something as basic as Synergistic Research Master Coupler will be a profound improvement. Hardwire one of those directly to wherever the existing terminates inside the chassis, huge improvement.

Adding an IEC inlet will not help anything. It will only add another point of (I^2)*R (or more precisely, (i^2)*z) power transfer loss. You will not want to put an over-sized power cord on your equipment either, as it lessens the ability of the power supply’s filtering circuitry to reject noise proportionally as the cord impedance drops (ie false economy). 

I don't know sleepwalker65 if you're one who has yet to realize the value of a good power cord, or you can't see the forest for the trees. Either way, check it out: The improvement going from old oxidized lamp cord to a new high end power cord is many orders of magnitude greater than any possible losses from adding another connection. Heck you could twist the wires by hand and still be better off with a good power cord. You could for that matter throw ANY aftermarket power cord on there and be a whole lot better than the old lamp cord that's on there now.

I agree that the cleanest way is to avoid using an IEC socket, and instead replace the cord straight into the power supply.

Don't go crazy on wire size either. If you must increase the hole size, make sure you secure an appropriate grommet.

@millercarbon everyone knows that aftermarket power cords are for people who have nothing else to occupy their time. It’s very simple: meet the demands for current supply without a significant voltage drop. As I said before, some voltage drop over the power cord is definitely desirable, as the input impedance of the power supply should be lower than the power cord above 60Hz.