Yes. BTW, did you ever swap the tubes between the two channels to see if the problem is with one of the tubes?

Okay. At least you are down to one board. Since the right one is fine, it is just a matter of tracking down the difference between the two. I would verify your ground connections on the screw headers are making contact properly (no cold soldier joints, etc...). Using a multimeter, can you...

I think you should do what fishski13 is recommending and take the entire input section, including the pot, out of the equation and see where things lie. I am a fan of wiring input signal grounds to the pot sperately and maintaining them separately all the way into the input(s) of the amp...

Interesting. Do you have the left and right signal grounds tied together at the inputs? If not, are they tied together at the pot?

The gloss requirement is the tough part. Otherwise, the material used to spray truck bedliners would meet your requirements. I've seen a fellow member use it on a set of speakers and I thought it turned out great. Looked good and is durable beyond belief.

At this point, I think you need to consider isolating each channel separately and see if you can narrow things down a bit. By that, I mean electronically disconnect one channel and see if both channels exhibit the hum independently. Even if they do, it should be easier, at least in theory, to...

You are not the only one confused. Did you follow the alternate grounding scheme or not? Follow the alternate grounding scheme and establish a reference. In this configuration, which channel exhibits a hum?

You connected the center tap of your transformer to what ground???

I would advise you first verify the hum is not internally generated before moving outwards. Be advised, I would NOT use your good headphones for ANY initial testing. There are plenty of cheap, disposable headphones on the market for this task. First, ground the inputs. I like to use a pair of...

I would also recommend you try the alternate wiring scheme for the signal ground as outlined on Alex's site. I personally had better success with the alternate wiring scheme.

You do not have to use an e12. You could just let the amp warm up and the bias settle before plugging in the headphones. I would advise you do that anyway, even with an e12. You need two e12 as the EHHA rev A boards have independent power supplies. One e12 for each supply. You could get by with...

Well, that certainly is not expected. What does your bias measure on each side?

I'll second TomBs recommendation, changing out the rectifiers as well as adding the snubber caps makes a significant difference in the noise floor of the amplifier. Using different rectifiers is a no-brainer. Adding the snubbers is quite straightforward if you attach them to the underside of...

The use of sockets should not have any bearing on the chassis height. The legs of the output devices would be trimmed appropriately to fit the heatsinks while retaining a tight fit within the sockets. Ideally, or at least how I would do it, the heatsinks themselves would not be soldered down...

Does he have a tube tester? If so, what parameter(s) does it test? Since you are most likely not testing the tubes at the operational parameters in which they will be used, the best you can do is approximate their relative performance against a known reference; hence the tube tester.