I see you installed both the 68K and 220K on the output area, I normally don't install the 68K ones but I don't think that is the problem. I have seen them supply 68K for the ones in the 220K position, are you sure those are correct? It sounds super distorted like the output is overloaded.

Can you share pictures of your build with as much detail as possible. And yeah something is seriously wrong!

Yes, you are creating a virtual center tap with the two 100ohm 2W resistors. On that tag strip, one end of each resistor goes to each of the heater wires, the other end to the star ground point.

But no, you can't just tie the grids together, you have to sum the channels with a resistor network. Google will show examples of this.

I can't recommend highly enough buying a real mono cart and make sure it's actually a horizonal only cart that doesn't read vertical movement for use with mono vinyl. Vertical compliance is fine, but some mono carts are just stereo carts with the outputs summed. The AT33mono is a real mono cart I swear by. https://dgmono.com/mono-cartridge-database/

I did find some shorter world's best cables that were made with some sort of special low capacitance wire. That worked good, but yeah just normal. RCA cables are usually way too high. Capacitance.

There is none added, the loading is set by the cables as you noted. I see all these pre-amps with dip switches to add capacitance and almost no modern carts need anything more than what the cables provide and honestly, you have to be careful as many cables will over load the cart due to their high capacitance!

Thanks for the post!! I'm excited about working on your 2A3 amp!

Yes, that would work too and doesn't need to be MBB.

Yep, that would work too. Make sure it's a MBB or "Make before break" switch, sometimes called a "Shorting" switch. You don't want the cathode to go open between the two positions. It probably wouldn't kill anything, but it's best practice.

Yeah, that appears to be just a normal inline ma meter. You could add a simple bypass switch to the meter so it is bypassed when not being used to check the current. A DPDT could be used to bypass two meters.

As you said, they all sound different so it's very subjective! Part of this should be based on an honest assessment of your power needs. I find most people overestimate this, including myself! A 3-4W amp will provide all the power I really need.

I would not want to leave a meter in the signal path, maybe if it has a bypass switch?

It's looking great!!!

That's all fine.

Yeah sorry about that, this forum now has so many spam posts daily I had to set every post needs approval. It's starting to get overwhelming :(

Ground one lead and the start looking for DC, first on each side of the choke and then on the other large resistors and try to see where the voltage disappears.

No sure where you got the spec that choke is only rated for 20V. It's rated for 300V.

And if those don't resolve it, there is something about that PC board causing it.

To understand how wiring/layout can impact a tube amp, just look at my recent mod series on that nosound 6P1. Some simple wire routing caused the amp to start oscillating. This noise you talk about could easily be related to the PC board trace layout. If swapping the tubes from left to right doesn't cause the problem to move to the other channel, the only thing left is how the amp is constructed. The main change you made it appears was this PC board. And my point was you didn't mention the fairly large change in the amp design until several posts into this thread and still don't seem to think that is related to the problem. The only other thing I could see might be related to the output transformers you used, try swapping them left to right and see if the noise/problem follows them.