Quick power cord question:

Hi Ho  Silver Away!

Don't ever do that again.

Who knows why the tubes are brighter?
Not exactly strong current affairs. 

silly season persists

The filaments are usually 6.3 or 12 VAC unregulated. If you really want to do a quantitative test, put a voltmeter on the filament supply and measure the value with the old and new cords.

What sisemans said. 

The true test, is to replace the kettle power cord, with your .99999 Silver
DIY, boil some water and make a cup of tea. Is it a better tea than the one with the 1.50$ original power cord?

For your attention:
Silver conducts only 5% better than copper. 
Silver cost is 130 times more than copper. So you did a bad deal...
You could gain the same conductivity with 5% more cross section in the copper wire, for 130 times less the price!
I don't know about silver, but copper that goes to the electric industry, is by STD 99.98% pure copper. The rest 0.02% has no significant on conductivity. 

I don't know about the law in your country, in mine, you need to have an electrician certificate to do a power job. If someone get shocked from a none certified cable, it is punishable with jail time.