You can buy them on Amazon I believe.
You can also use a monitor that has one built in, like most CRT computer monitors. Put the CRTs face to face, turn on the computer monitor and it will degauss itself, and in turn can degauss the TV with the same magnetic field.
Do some consumer TVs have built-in degaussing coils?
Yup, some have it for sure. If you can get into the service menu there may be an option for it.
Check in the service manual if you have a copy.
Would something like this work?
https://www.ebay.com/itm/273557522858?hash=item3fb14c89aa:g:eaMAAOSwZddb6WNg
Also, how would you get into the service menu on a Dynex DX-R20TR?
Maybe… I have never used one, so I’m not the right person to ask.
I don’t know how to get into the service menu, you would need to find a service manual online.
My Xbox 360 PSU did this to my CRT. So it’s not just speakers. It’s anything with a magnet or anything generating enough electric interference.
What exactly is positioned lower left of your TV? Unless that’s moved this will keep happening.
I recently got this TV; it was like this when I picked it up. I have moved it to a place where there is nothing below the TV, and it’s still there.
Sure thing. It won’t go until it is treated.
But good to know it’s not caused by your setup.
Nearly all color TVs have built in degaussing coils. That’s the “bwonk” you hear when you turn on the TV.
If you have a discolored corner it’s likely not fixable. If it’s fixable at all it’d require doing work inside the TV to adjust magnets and likely adding on “bodge” magnets which would ruin the geometry of the screen.
Still some uncertainty there. 
I would not trust those.
You really need one that is in the shape of a ring, but I’ve been looking for one myself for some time and not come across a good one, so no idea where to direct you to buy one either.
I’m pretty sure just moving the purity ring would move that little amount of discoloration out, though if you do this beware that it may also knock about your geometry so you’d want to get access to a service menu of sorts first.
My old 240v to 110v step down transformer used to do the same sort of thing to my PVM even from over a metre distance away… So do ensure it is away from anything that could could cause EMI, but it also wont go immediately after moving. Hence power cycling a lot can help as it should trigger a degauss if one is built in as already mentioned.
As for getting into the service menu try out these instructions:
https://factory-reset.com/wiki/Dynex_Service_Menu
Let us know if these methods work and if possible give us some screen shots of the service menu as it could give us a better idea if it would be possible to fix via it.
I tried both codes when the TV was off as well as when the TV was on and it didn’t bring me to the service menu. I will try power cycling it.
I contacted Dynex, and apparently this TV is lacking a service menu. I put my other CRT right in front of it and have been using the other TV’S built-in degausser. I’ll tell you if I get good results.
Huh. That’s a neat trick, hopefully it works.
It doesn’t seemed to have worked. I ordered a degaussing coil online.
off question, but - the speaker on my CR has seemingly gone out. i’d not noticed since it’s hooked into the receiver, but now that i have a partner playing on it (while i use the HDTV for ps5/switch etc) i need another option. what’s a good standalone option here? just need small speakers/etc i could maybe piggyback off the stereo AV ones or something similar
The degaussing coil came, and it doesn’t seem to have fixed the issue. Do used consumer CRTs often have issues?
It could have been knocked over or dropped by the previous owner. Have you tried placing magnets on it yet?
