The amp is 99% functioning, but has a strange issue where the volume and tone pots interact and affect voltage (I measured plate voltage in the video but voltage at B+ nodes also affected) and create lots of loud noise. This only happens on the top 5% of the volume pot, when tone pot is also turned all the way up. With tone rolled back, but volume at full no issue. With volume rolled back and tone turned all the way up, no issue.
The following are the original schematic, a voltage chart comparing 2 of the same type of amp - but one working and without this issue (#1), to this amp (#2). The voltage chart says ef86 xtra, but this isn't that circuit, they just have the same tubes so I used that chart. And a video showing the problem using my DMM measuring plate voltage at the el84 v4.
Any ideas of what it can be? Any tests I need to complete to explore the problem?
![Image](https://i.imgur.com/9KHvhjL.jpg)
![Image](https://i.imgur.com/YMqzhJP.jpg)
https://youtu.be/thw_kuXHLIo