Seems you are using a tube based rectifier instead of the the solid state rectifier shown in the schematics.
That will significantly drop all the voltages, starting at point A.
Using a quick PSU Designer II simulation I get about 40 volts lower using a 5U4G vs. 1N4007 in full wave mode.
Are you using the same series resistor values on the output of the rectifier that are shown in the ZKIT-1 schematic? 1K and 6.8K?

This time I built the zen exactly as shown in the Decware videos on youtube; same values throughout, tube rectifier and still had hum.

yep, I had read and tried that, thanks! Even though the transformer has a center tap... I also installed all kinds of wires between the volume pot and the rca ground lugs.
With the diodes in place I had the same hum, however I did not measure the voltages for fear of electric shock I got over that fear yesterday.
I somehow take it for granted that low power supply from the psu WILL cause hum, am I wrong?
two quick questions: should I lower the 1k 6w to increase voltage and if so, by how much? I have other 1k 6w resistors on hand.
And second: I replaced the 2x 20uf electrolytic caps in series with one 15uf film cap. I do not understand the idea behind those 2 electrolytics, except perhaps to bridge a long distance inside the chassis????
Thanks

Sorry but I do not have the tube experience to know whether the low voltage "would" cause the hum.
I suppose it's possible but I would expect high ripple on the B+ supply or noise on the inputs to be a more likely cause.
I do know that from my reading you should ground everything at one point, AND ONE POINT ONLY to the chassis, not have several places around the top plate grounding components. That includes the RCA connector mounting I believe. Possibly a common point of error.
The series electrolytics effectively double the voltage rating of each, while halving the capacitance to 10uF. A single high voltage 15uF cap will be fine there.
To raise the voltage levels you can reduce the series resistors values some but I would be careful not to go too far too quickly.
Placing another 1K 6W in parallel with the original one may raise the voltage too high and damage something.
I would need to run a simulation to see what is a good choice to try.
Do you have any other 6W resistors on hand?

please run the simulation if you have a moment, it might mean a breakthrough in a cold case

could go down to 800ohm, if I solder 1k and 2x 10k in parallel

I see, so after all 500ohm instead of 1k in that position seems ok? I can go straight for that. Yes, I loathe measuring voltages! I'm off to soldering those in then. I will use a kiwame 5w 1k, i think 5w should be ok? what do you think?

otherwise I have those 6w 1k mexican resistors that Steve uses, DALE I believe, they seem to be covered in tar

yes, i always discharge the caps, Even the itsy bitsy ones, just to be safe  I'm off to soldering then, will post results right after the headphone test. Your help is priceless, thank you again

I see what you mean, however I swear it does not   I have just added the 1k on piggy back, connecting cables

So voltage is most likely not the issue.
You can check to see if the volts did go up some as I simulated if you want.
So I would look for grounding issues.
Where in the picture is your central "star" ground point?
And, have you pulled both inputs off the RCAs and tried running the volume up and down to see if the noise is coming from the inputs or after the preamp tube?

I have just swapped the input tube to 6922. same hum.

Could I have a faulty transformer?

hum is the same in both channels, I'm going to do the input tube trick now

It's beginning to tell me I don't know what I am doing  :)
Unfortunately we have only eliminated a couple of possible sources and there are a few that are hard to isolate.
Sorry but I am running out of ideas.
You say this is the same on all your Zen amp builds?
How many would that be?
Seems possibly the problem is outside the amps.
Do your speakers have powered subs?
Is there any hum using a different amp but all other components and interconnects being exactly the same?

that should read: lowered to 10uf

Hi Core32,

I have used resistance in parallel with the headphones to lower the impedance to 8ohm (headphone imp. is 62@). The hum remains the same. I have to use above 100ohm in series with the headphones to get rid of it. I don't know what that does in terms of mismatched impedance, but Steve seems to say it doesn't matter, as he suggested I use as much as I need to get rid of the noise.
So maybe you re right, this is as much silence as I can obtain from the amp. I am glad you helped me get the voltages on track, i will measure them this week end. Thank you very much!