Looking good ! I've build quite a few of these (one a couple of weeks ago yet to be posted) and they don't hum.
Things to try ... make up a shorted out set of RCA plugs and power up the amp with the inputs shorted.
If the hum is gone, the problem is before the amp. What are you feeding it with? If it's a preamp, does
it have any connection to ground via TV Cable or a computer with a grounded cord?
If the hum is still there with the inputs shorted, dress your wires to keep any AC away from audio,
including the feedback connections. You might try lifting the chassis ground from the ST-35 board.
Using the terminal blocks makes things easier if a mod needs to be done later, you can remove the
board from the chassis in about 20 seconds.
You might want to grab some stainless steel 1/4" machine screws from the hardware store, it will
make the top of the chassis loook much nicer than the zinc flathead screws, and the chassis won't
get scratched up when the screwdriver slips.
... tom