From this To this

I have also wired output tranformers as autoformers.   First I moved primary GND tap to unused pin next to old pin.     And then used jumper wires to connect it to 300 ohm pin.  

I made adapters for 6E6P tubes     First I tried 6E5P tubes and liked how they sound, but heaters resistance was so low it triggered heater regulators overcurrent protection when tubes were cold. To get around this I turned amp on with one tube plugged in and let tube warm. Then turned amp...

Diffence in sound was about same when I changed bias LEDs. I measured transistors hFE using multimeter, for 2N5087's it was about 330 while BC560C's measured about 590. For anyone doing this mod, BC560's have different pinout, so they go backwards on board compared to 2N5087's. I used...

I wanted to try increasing CCS impedance, so I changed 2N5087 transistors to BC560C. I also changed bias transistors to BC560C. And again sound got better.

I am not very good at describing sound, but I can hear new things from music and everything seems little bit clearer. Plate voltage increased about 10V, it is now around 180 and 170V. I am using Russian 6N15P tubes and plate voltage with these tubes is higher than any other tube I have tried.

I changed bias setting LEDs (D10, D11) to green ones (http://www.mouser.com/ds/2/239/_100_LTL2R3KGKNN-53107.pdf) and sound got better. With standard red LEDs bias was 2.25V now it is 2.47V.

I noticed that power transformer was making more noise because metal box was touching it. So I moved C1 further away from transformer and made little bit bigger box.  

It was audible with Sennheiser HD800 in high Z setting. With Denon D2000 I didn't hear any hum. With music playing I didn't notice it but when music paused it was quite noticeable.  

Power transformer box has those perforations only on top. Box is touching transformer from one side because C1 is so close to transformer. There is dielectric material between transformer and box. IEC inlet side and two other sides have small gap between box and transformer for air flow...

I just used some leftover sheet metal pieces which I had and welded them together. Power transformer box I tried to make so that there would be some ventilation. Its inside dimensions are few millimeters bigger than transformer itself and there are small feets which leave gap between circuit...

Today I made box for power transformer and now hum is gone. I also tried only shielding power transformer and leaving output transformers naked. It did reduce more hum than shielding only output transformers. But there was still very small amount of hum left, which disappeared when...

I have grounded those heatsinks. With only heatsinks grounded there was noticeable hum. When I added that metal box hum was reduced to level where I have to listen closely to notice it.  

Here is my attempt to reduce hum It is grounded metal box that covers output transformers. It almost completely removed hum.