I'll second that shielded cable does absolutely nothing to quiet a 5E3. Keep it simple. Separating the pre and power amp grounds is pretty important. I didn't use the brass plate on the couple of builds I did. If you're placing another parts order try 30-16-10 on the filter caps. Lowering the filtering on the preamp doesn't add any hum and helps the amp respond in a looser, more interesting way. If the bright channel is a little harsh try changing the .005 bypass cap to 47pF. That lets just enough highs around the volume pot to prevent it from sounding dull when turned down.