M. Gregg wrote:
NB your DC supply will need to be referenced either to a B+ voltage lift or a false centre tap across the supply with ground ref or voltage lift.
It depends if the tubes are "stacked" or where a cathode is at higher voltage above ground.
If you don't it will hum.
This is an important step to removing you hum/buzz, create a "vertual" center tap on the 6.3v winding of the transformer using 2x 100 ohm 0.5watt resistors, one resistor on each side of the winding to ground. I personally have forgotten to do this many times in the past, with AC heaters you will get a lower frequency hum (60hz I believe) with DC heaters it will be a distinctive "buzz" around 120hz? plus harmonics injected into the supply. It can sound like you have a bad ground when you turn your volume up but it is actually noise being injected through the cathode into the grid it seems... some one else could probably elaborate or correct me on that.
Put 0.1uF caps across (parallel) to the diodes like suggested as well as 0.1uF caps across each electrolytic and you should be
