I'm not clear if this is the right place to post this.
I designed and built a 2A3 amp.
6SL7 input tube in SRPP directly coupled (Loftin White) into 2A3 running about 50mA bias, AC heaters.
I have a hum in the right channel with no input connected that goes away once the volume pot (100K, Alps Blue Velvet) reaches about 1/3 volume. To clarify the noise is there from 0 -1/3 at constant volume then quickly fades out and it gone up to full volume.
My first assumption is this has to be a ground issue, but I'm unclear how that could be only on the right channel.
I'm at a bit of a loss as to where to start to try and track this down.
Everything is grounded through a busbar running down the center of the amp.
Any Suggestions
I designed and built a 2A3 amp.
6SL7 input tube in SRPP directly coupled (Loftin White) into 2A3 running about 50mA bias, AC heaters.
I have a hum in the right channel with no input connected that goes away once the volume pot (100K, Alps Blue Velvet) reaches about 1/3 volume. To clarify the noise is there from 0 -1/3 at constant volume then quickly fades out and it gone up to full volume.
My first assumption is this has to be a ground issue, but I'm unclear how that could be only on the right channel.
I'm at a bit of a loss as to where to start to try and track this down.
Everything is grounded through a busbar running down the center of the amp.
Any Suggestions
Moved to Tubes / Valves forum. 
Where is the bus connected to the chassis?
Is the input socket isolated from the chassis?
Post some photos.
Is the input socket isolated from the chassis?
Post some photos.
Not currently, but it's an easy fix and I'll try it.
but what stops me suspecting this is the fact it's just the right channel, and both inputs are next to each other.
And this it's what's really confusing me, if both channels were impacted I'd assume it was an isolation issue.
In the corner, but also where power comes in.
In effect at both ends.
Note the tidiest build ever, note it has 2 independent power supplies, the extra purple wire running to the 2A3 socket for the left channel is the center tap for the 2.5V supply, it's disconnected. The extra wire to the 6SL7 heater is a ~50V lift to keep the Heater/Cathode difference in spec.
The two terminal strips at the top are all ground, that was my first thought, but I've tried directly connecting them, and there is no change.
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Only ground the bus at the power end of the chassis. Isolate the other end of the bus from the chassis.
Also isolate the input jacks from the chassis.
Also isolate the input jacks from the chassis.
The switch should go near the power entrance, and shorten its wiring. What is it for?
That could be the main source of hum, so try that first.
Maybe you can lift the terminal strip near the inputs from the chassis, at least for a test.
Looks like the RCAs are insulated already, no? There seems to be several ground loops
due to the top terminal strips.
That could be the main source of hum, so try that first.
Maybe you can lift the terminal strip near the inputs from the chassis, at least for a test.
Looks like the RCAs are insulated already, no? There seems to be several ground loops
due to the top terminal strips.
It's not a switch on the thing on the top right is the headphone socket
Bottom two jacks are power.
They deliberately weren't (obviously not my best call), the ground connection was under the isolation washer.
They are both lifted, they just don't look that way in the image, there is insulation under each, and a wire run across the bottom to turn them into effectively remote bus bars, it was just easier than trying to route everything to the center of the Chasis.
I don't think so, with the inputs lifted, it basically just a tree.
The center bus runs out to the two terminal strips that act as an additional bus.
Though it retrospect, it wouldn't be that hard to run all the lines individually back to the bus.
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This should be ok if the terminal strips are secure.
Theoretically, the best way is with both input sockets bonded directly to the chassis, but in practice this is hard
to make work well. So almost universally the inputs are isolated.
Theoretically, the best way is with both input sockets bonded directly to the chassis, but in practice this is hard
to make work well. So almost universally the inputs are isolated.