Hum is probably caused by mains transformer but reflected on audio transformers. Try to move around T1. I doubt that heater voltage can cause hum with 6BC8. Of course that trim have to change voltage of 3 pin regulator.test - wired one channel, with regular two deck pots. it works! but I have this hum that is a bit annoying. the trimpot on the heater board has no effect on the voltage, should it ?
Measure the voltage before regulator. If you have 6.3V unloaded and you measure big drop after loading than your transformer can't do the job. If you don't have a big drop when it's loaded try to skip (short) the 1. 0.22ohm resistor, it may help a bit to reach 6.3Vfilament voltage is only around 5, 7 volts, can't get this higher ?!?
Pynta Studios said:Did anyone see this: http://dripelectronics.com/660.html?
Seems like a very cool way to get it done with good parts and much less soldering!