Just to make sure that I understand, does the hum come from both channels? And have you shorted the inputs when you test the amp? If the hum comes from one channel only then that would lead in a different direction.

Good point about the volume control. FWIW, I see that there may be another hole for the volume control to be mounted right about the input on the board. This would move the sensitive signal wires away from the AC, at least better than they are now. I know, it is a tighter fit, but the reasoning will prove itself. You could even remove the volume control from the present place on the chassis, away from where it is now, just to see if it has an effect on the hum.

I have rebuilt my amp and chassis (see pics).  I used a different POT, with solder lugs but same specs as orig.  

I also grounded the POT to the board (see pic).  This helped - about 40% better now.

I still have hum that increases with volume, even though the preamp driving the input is connected but powered off.

When I disconnect both RCA inputs, there is a slight hum but it does not increase with Volume.  

Here are some measurements on the new amp:

A = measured - 343 vdc, s/b 346 +/- 10VDC

B = measured - 310 vdc, s/b 309 +/- 10 VDC.

C = measured 10 vdc , s/b 10.25 +/- 2 VDC.

D pin 3 6922  measured 2.38 vdc,  s/b 2.6 +/- 1/2 VDC.

D pin 8 6922 measured 2.4 vdc, s/b/ 2.6 +/- 1/2 VDC

Output Tube Bias current - calculated by measuring the voltage drop across 150 ohm 5W resistor = 66 mA

Any feedback is greatly appreciated.  Thanks.

ok I'm reposting the pics of version 2 of the amp.  Thanks for reaching out.

Actually, pics 2, 4, and 5 show 120Hz signal awhile pic6 at the speaker terminals shows a 60Hz signal. I've read that 120Hz hum may indicate ground loop problem. Any ideas here??  Thanks in advance.

All in all, there is only one thing that keeps poking me in the side, and that is about the volume control. I am also going to tell you that it isn't real likely that this is your problem, but I think that it needs replaced and the wires as well. The reason that this is on my mind is that before you can move on, the possibility of this being an issue has to be dealt with first. Let me just say that it takes less heat to solder finer wire (which is all that is needed in this case) than it does thick wire, such as you have used here. You might find that 22-24 gauge solid core wire will be easier to work with too. Stranded wire can 'reach' all over the place and make contact where it shouldn't. Secondly, changing the control itself will give you an opportunity to buy a better pot. Yes, I am being picky here. It is just that the better pots are more robust and some are sealed to prevent dirt from entering the pot. Since you are into the piece working things over, this is a chance to rectify two things that, while not necessarily the problem, don't help in the overall scheme of things. I am not sure that a pot needs to be grounded if it is already making contact with the chassis, but since you said that there was reduction in hum after doing this, it throws more of my concern in the direction of the pot to begin with.

Just a suggestion, why not drill the pot hole out a bit. You’ll be left with an oval hole. You can real thin Teflon washers at the big box store, simply hide the enlongated hole with the washer. I really admire the work you’ve done, I made a set of rca’s last night and that tops out my stress level for having the solder station on. It cramps my neck up something fierce.

Today, I performed an experiment.  I disconnected the POT entirely, and removed all wires from the POT including the ground wire.  Then I soldered it directly to the board - of course the POT is now upside down so the volume orientation is flipped - turn POT to the left to increase the volume instead of decrease it etc.  Just wanted to remove wiring 100% from the equation.

Unfortunately, the noise is still present with no improvement.

Admittedly, it's only noticeable during extremely quiet music (and track transition dead space) but it still bothers me and I want to get to the bottom of it. I'm a perfectionist

So, I have to conclude one of 3 things:

1. I have a cheap POT
2. I am hearing inherent noise in the design (hard to accept)
3. I may have a ground loop problem.

Next step is to install the ALPS 100K POT - I've read good things about the quality.  Should be better than my $2 POT (no PUN)

Regarding the possibility of a ground loop: I have the ground from the IEC directly connected to the chassis.  I have board GND connected to the chassis via one of the screws holding my Power Transformer to the chassis, only a couple inches away.  Any concerns there??

As always, many thanks to everyone for your comments and feedback.

You will hear very slight 120hz hum at speaker cone, louder or soft depending on speaker efficiency, but at a fixed level, independent of volume. This is from the power supply and normal. Loads of threads about adding capacitance choke etc if that’s your thing.

My experience is that those little pots are notoriously fragile. I would suggest physically removing pot for testing. Put a 100k from input to ground when you do this. You can use an external volume at source. Sometimes grounding the case of the pot helps, even the heat of soldering to the case can cause problems tho… Wiggle the pot and its body with amp playing…. If you still have the loud hum I’d check / reflow solder joints everywhere, if it varies in volume you may have a ground loop somewhere.