Crack + Speedball low hum and RF noise

[Tofu]

Good afternoon folks,
I finally have my crack with speedball complete, ran into some issues during the build process that were mainly my fault and I was able to work through (painted wrong side of top plate, miswired the octet socket on initial build, tripped a fuse, had a capacitor leg break during speedball upgrade), and everything is working great now aside from two small issues.

First, there's a very low hum which is present regardless of RCA input and volume knob makes no difference. It's low enough that I don't notice it when music is playing unless it's a very quiet piece and even then it's largely ignorable. My guess is this has something to do with either my mains power or something with my wiring/solder joints.
I went over every joint and made sure it had plenty of solder and wasn't a cold joint, I did this during speedball upgrade as I couldn't get readings off the large board, but I think the capacitors were charged and that caused an issue, eventually was able to get good readings.
Is there any way to test if it's the house mains aside from taking it to another physical location? Or would that require more expensive testing equipment

Secondly, I have some RF interference noise if I use a Genalex Gold Lion ECC82 tube, however If I use the stock RCA tube then I only get the above low hum. tried the same troubleshooting for the noise, it ignores volume knob and RCAs (my first thought was ground loop noise coming from my laptop somehow), but nothing seems to affect it.
While I don't mind using the RCA tube it makes me a little sad I can't really use a tube I paid 30-40 bucks for. Could the tube itself be bad somehow?

Otherwise I'm quite happy with my build so far (and yes I know, mirrored is highly discouraged, but it's working and wired per the manual), need to apply more sealcoat to the wood to get some gloss going, but I'm super stoked with how the stain turned out (picture makes it look more dull than it really is). Paint on the top plate has a couple of blemishes but ah well, I can live with it. Attached some pictures for review, since then I've changed the RCA cables to ones with 90s on one end, looks much cleaner though did nothing really for the sound.

[Paul Birkeland]

You could try adding this to see if it helps at all:
https://forum.bottlehead.com/index.php?topic=11676.0

Since you did not follow the kit layout, your mileage may vary in terms of how quiet you can get it. 

[Tofu]

You could try adding this to see if it helps at all:
https://forum.bottlehead.com/index.php?topic=11676.0

Since you did not follow the kit layout, your mileage may vary in terms of how quiet you can get it.

Gotcha, yeah, also thought it might be something intrinsic to the layout since it's not the stock layout.
Thanks for the suggestion I'll make the order and see if helps, if not then ah well I can live with it, I quite like the volume knob being on the right for some reason.

Since I want to save on shipping cost I'll probably get some cap upgrades as well, currently looking at Panasonic EZP-E50107MTA 100uf500VDC
From what I'm reading I'm not 100% sure if it's worthwhile to upgrade the power supply caps, can anyone chime in on their thoughts? Otherwise I'll probably just get a couple spare stock-like caps in case I break another leg.

[Thermioniclife]

The caps they use in the power supply are well suited for the purpose, and good quality,no need to replace them.
The only upgrade that may make a difference would be to use polypropylene in oil but the physical size of them are tremendous.
Picture the size of a beer can or larger.

[Paul Birkeland]

If you want to use those for coupling caps, go for it!  You may find that you can find something a lot smaller that carries a low voltage rating, but then again maybe not. 

[Tofu]

The caps they use in the power supply are well suited for the purpose, and good quality,no need to replace them.
The only upgrade that may make a difference would be to use polypropylene in oil but the physical size of them are tremendous.
Picture the size of a beer can or larger.

Gotcha, that's kinda what I figured, thanks for the input.
I'll just grab a spare or two to have on hand.

If you want to use those for coupling caps, go for it!  You may find that you can find something a lot smaller that carries a low voltage rating, but then again maybe not.

Yeah, I feel like I could find smaller that would be just as good, but that would require hours of research into brands, types, ratings, etc..
These were used in another build and work well apparently, and the square shape makes mounting a little easier, so figured I'd save myself some time.

[Tofu]

I have now completed my cap upgrade with bypass caps, and also implemented that diode mod and it seemed to help... at first.
Most of the time I have the noise issues are later at night when everything is quiet, lo and behold it came back same as ever, which made me a sad panda except this time I noticed something.
When I put my hand near the tube, the noise went away, which makes me think that the tube is picking up some sort of RF interference, and after setting everything I could to airplane mode, disabling wifi, etc.. I finally found makeshift solution:
I put a steel cup upside down over the tube, and noise was immediately gone. There's the faintest hum of a low frequency, but that's easily ignorable. As a side note, I don't know if it's the caps or the diode mod, but putting the volume pot to 100% I no longer have any noise, though that was never an issue, just an interesting finding. (Would previously get a small amount of noise but I can't even push the volume past 50% without getting too loud)

With all this in mind, would there be any heat concerns with the tube enclosed like this? I may eventually find some way to make a small faraday cage for the tube as an REI cup over the tube is pretty goofy, I'm open to ideas if anyone has any.

Finally I have my sonic bliss, sans annoying blips from god knows where.

[Doc B.]

An IERC tube shield over a bayonet style tube socket ring would be a solution. Or find a tube that is less RF sensitive.

[Paul Birkeland]

Do you have grounded outlets where you are using this amp?  Did you paint the bottom side of the chassis, are the screws tight? 

When your hand by a tube starts wildly changing noise you are hearing, I immediately start to think that there's an earthing issue at work.

[Tofu]

An IERC tube shield over a bayonet style tube socket ring would be a solution. Or find a tube that is less RF sensitive.

I'll have to look into it, looks like a good option. Currently still recovering from the amp and upgrades before looking into more tubes to roll.
Is this what you're referring to? https://www.tubedepot.com/products/9-pin-miniature-socket-with-shield

Do you have grounded outlets where you are using this amp?  Did you paint the bottom side of the chassis, are the screws tight? 

When your hand by a tube starts wildly changing noise you are hearing, I immediately start to think that there's an earthing issue at work.

Plug is grounded, bottom of plate is bare, bell end had paint sanded off around the screws, all screws tight. I'd be inclined to agree if my hand introduced noise, rather than eliminate it, but I lack the knowledge/experience to say for certain.
There is a cell tower about half a block from my house which may be contributing to it.

[Paul Birkeland]

A tube shield may be just the ticket.  The generic new shields with bases that you can buy at all the major tube suppliers have the appropriate piece of metal to mount in place of the right that holes the socket to the chassis.  The shield that Doc B. recommended should slide right over that metal collar and may indeed be just the ticket for what you're experiencing. 

[Tofu]

Received the tube shield, it was a little tricky getting the new base cover on but it did solve the interference issue, plus I got it in red so it matches my build nicely.

Only issue now is the hum seems to have gotten worse, or it's just more noticeable without the blip noises, and it's louder on the right channel.
I looked through and re-soldered anything that looked suspicious, paying extra attention to the right channel, I verified the ground path, no resistance at all points in the sticky post about checking ground.
I also tried cleaning up the contacts using a brass brush and no luck.

My only suspicion is the 12AU7 tube itself, as when I originally built my crack I made a wiring mistake and connected pins 2 and 3 on the 9 pin socket, could this have somehow damaged the tube itself?
Part of why I suspect the tube is that tapping the tube will change the sound and sometimes make it go away for about 10-20 seconds.
Sadly I don't have any tubes to swap out and verify this yet, though I do have a Russian 6N13S on the way that supposedly will arrive the first or second week of June (overseas ordering is an act of extreme patience)

[Paul Birkeland]

Connecting pins 2 and 3 could have done something weird to the tube.

If you tap on it and the noise goes away, that does tend to suggest a soldering issue in the amp or really dirty tube pins.  Certainly trying a second 12AU7 is a good idea.