I had the same exact experienced as you faced..
I ordered pair of monos 300b PSE at about 3k.. I fabricated my own top plate and added some components and sent to him.
When I got the system back in Jan 2019, it was a total dissapointing.
Hooked them up, and there was sound and no noise.. That's a bit relief..
However the workmanship and material used is totally bad. The placement of components is rather scattered.
So I decided to rebuild the unit.. I tried to get schematic from him but he provided not accurate and many missing info.
He even condemned me not to do anything if I'm not familiar.
Yes, I'm not familiar with tube amp design but I'm good at electronics and DIY stuff.. Then he was not cooperative..
I then started to draft the schematic from the system. I asked many stupid question from others and friends..
And I'm almost done with them now.. And prayed and hope it will be good..
I then tried to find info on this Ken from various search..
I find out that he is Vietnamese lives in Japan, that's trigger me why he does speak like a Jap in his email.
He collect old audio system, recondition them and sell. He also collect tone arms and sell them. These items are good to buy with careful clarification and know what u are getting.
On the tube amps he build are just based on clone and some own modifications. Workmanship sucks. And totally not recommended to consider.