[quote name='peted' post='510275' date='Jun 10 2009, 03:37 PM']I would suspect the cable if the head is silent until it's plugged in.
How is the hiss with no cable, and the valve drive + volume at full?[/quote]
With the valve dial on full and the input and output on full with no cable attached it is silent.
With a cable plugged in, the valve, input and output set at 9pm, you can hear a hissing sound. If I turn the valve to full, or increase the treble dial, the hissing gets louder. I have tried different cables and there is no difference in the hissing sound