In the photos and wiring diagram for the SP14 the chassis has no safety ground connection and could become live in certain fault conditions. The exception is Roy's latest build photos posted in November 2013 where the bus bar wire appears to be connected to the chassis earth screw on the back next to the phono input jacks which makes sense to me. If I'm correct, in all the other builds, that screw is connected to the chassis but nothing else and therefore ineffective and the chassis is not safely grounded.
I started building my SP14 before I saw Roy's latest build photos and have earthed the chassis at the IEC socket and connected it to the bus bar wire via a "High Current Safety Loop Breaker ", also known as a "Hum-loop block network", which consists of a 10 ohm/5 watt resistor in parallel with a 100nF capacitor and a bridge diode to by-pass fault currents. When a ground loop is created it will now have a 10 ohm resistance in series with it, which should reduce power supply ground-loop currents to negligible levels, according to Valvewizard. See the links for details:
The Valvewizard article also gives good reasons why the ground-chassis connection should be close to the inputs as is the case in Roy's latest build photos. When I have finished my build I will report the results.