So I bought the Willsenton R-800i

I do experience the hum issue as well and I don´t know if it´s been there from the beginning or not, at least I noticed only after quite a while. After checking all possible component, cables, tubes etc. I also blame it on the tranformer. When I listen closely that´s also the place where it seems to come from. Unfortunately it´s louder with the Elrog 300Bs I´ve been using. Great tubes, but the hum is, well, it´s there. And it´s bothering me to the point where I found it difficult to listen to music. Well, having said that it´s still in the range where my girlfriend just shrugs, it´s basically not noticeable when music place (except for very quiet parts). There was some other issue with them and I´m waiting for a replacement pair, maybe that will change something.
I guess with that hum issue we´re entering real high end territory. If all parts are high qualtiy it just costs more. Considering value for money the R800i is hard to beat.

The RFTs would be really cheap, like under 10€ a piece, so I´d be ok with them not being a revelation.

Thanks for the info on the blue light in the 5U4C, that´s very helpful!

I’m sorry to hear folks have significant audible hum.  That’s frustrating. 
 

I have almost zero hum. I have to put my ear right above the transformer and it’s barely audible still. I think the transformer is potted. 
 

Have you sent a video of the hum to China Hifi?  I’d do that. They may be able to help.  I’d ask them if the transformer is potted too. 
 

I’ll look inside at the transformer when I open the unit up. 

Have already contacted China HiFi, here’s their response, “ Vacuum tube power amplifier and transistor power amplifier are different.  It's normal thatr hear the huming within 1-1.5m.”   So…I believe it is a function of quality of parts, particularly the transformers, and implementation, i.e., the build.  I’ve read the transformers are potted so not viable to upgrade with a mod.  

I have about 700 hours on my 300i, and it’s gotten slightly worse with time on the amp.  It’s much more noticeable with the 99 dB Klipsch Forte’s than the 92 dB Focal’s.  I think it would be unacceptable with LaScalas.  Yes, we’re beginning to migrate from really good mid-fi to more resolving, and expensive hi-fi!  That being said, I’m happy with the Willsenton with its noise floor vs price.  A high end build with much better parts would likely run $10k-$20k, depending on manufacturer.  It comes down to system synergy, the 300i has enough headroom to push 85-90 dB speakers with ease, that would be one solution.  Also with lower gain 12AT7s, I’ve found the hum isn’t noticeable at my seating position even between tracks.  Roll in a noisy high gain 12AX7 and the hum returns.  

As much as I hate to admit, Klipsch Heritage series may not be the best match for the Willsenton 300i.  My Inspire KT88 is a match with the Klipsch , dead silent! Problem is Dennis only builds a dozen or less amps a year. At the moment he has a 300b SET on ebay for $4,250, it won’t last long, maybe 48 hours. 

Anyway, glad I bought the Willsenton, great soundstage, deep bass, warm mids and crystal clear treble with the right pre stage tubes.  Sitting here right now listening with low level volume, a touch of boost at certain frequencies with a Klark Teknik DN360 studio equalizer and loving the mellow yet articulate sound emanating from the Focals.  

Cheers
 

I run Klipsch Heritage Cornwall IVs with the 800i 805 and it's near dead silent. Plus, if it were a transformer hum, the efficiency of your speakers may not matter--it would put that noise into the room without the speakers. 

Since you are running super efficient speakers, you could try going down from the 12ax7 to a 12au7 (that's the lowest gain in that 12 volt tube variety).

New to the thread but not the Willsenton 800i.  My amplifier creates no noticeable hum at what I consider normal listening volumes. My normal listening volume? Loud enough that you could, but wouldn't want to have a conversation. It would require some yelling.

I've rolled a few tubes in mine but I do want to say that this amplifier from the factory has a pretty good tube set in it. I think most would be 100% happy with how it sounds doing absolutely nothing to it. I also want to say that I purchased mine through China HiFi. Living in Boston, MA in the United States, DHL delivered the amplifier in 3 days after it was shipped!!! It took China HiFi 2 days to get it out the door. Outstanding!! The double boxing and packing materials were very well thought out and I'm not sure what else they could of done to safely ship it. Mine made it to my door safely. 

  Back to rolling tubes.  I have bolstered the midrange, added some definition to the high end and didn't hurt the low end at all. I based my selections off of recommendations because this being my first tube amp I do not come from a place of experience. The 12AX7 is now a Telefunken ECC83 EK, I changed the 274B but never noticed any audible difference with the tube I tried. The 805A I installed a set of Linlai Gold Elite E-805 and the 300B, I tried both a WE300B by Psvane and Genelex Gold Lion match set. I settled with the Genelex tube because the additional $450 for the WE300Bs weren't worth the extra $$$. Though they both sounded differently I liked them both differently. And last but not least I installed a set of Shuguang Cv-181 Black Treasures in the 6SN7 spots. This may be the biggest improvement of anything.

  Listening to voice forward recordings like Diana Krall's, When I look into your eyes, You feel her breath on the microphone. The holographic staging of the instruments is so defined. The realism of the piano as it plays from left to right across the room and cymbals that feel like you could reach out and mute them. It's very impressive. But them to spin Bridge of Sighs by Robin Trower, listening to Eye of the Eagle and Bridge of Sighs, it just blows me away how well it handles the 70s style rock guitar and Robin's almost horse voice then settles down to the heavy bass riff to end  Eye of the eagle. The beginning of Bridge of sighs showing off it's holographic strengths ringing around you. Again, strong baselines, great rock guitar riffs and Robin's voice just showcased as not all amplifiers can. The songs never sounding muddy or straining. Somehow throwing all that music at you but not being tiring. Displaying details out of the albums I didn't hear before. 

 And all this through a set of 87db KEF R3 Meta and an SVS Micro 3000 sub. It's a fantastic tube amp!