So I bought the Willsenton R-800i

I must admit that I still have to find the time to put the stock tubes back in. I started rolling more or less right away when I got the amp so I can´t say for sure if the Cossor is better than the factory 805 (now I´m using PSVane Acme 805s). It´s really on my list to check again how the stock tubes and some others I used for a while hold up against the combination I´m using at the moment. It´s been giving me great pleasure for months now so anything that may be a step back takes time I prefer to spend otherwise. I´ll get to that at some point.

But here´s two things I did do recently:

Before I realized that the stock tubes are 6H8C too I bought two pairs of the same for cheap online and put them in. One was really good and I during the past couple of weeks I double checked: It´s difficult (for me) to tell them apart from the Sylvania GTBs I also own. Both very sweet. The other russian pair seemed bland in comparison. But that´s what I heard about old russian NOS: Sometimes the quality is really good, sometimes not so much. For $10-15 a pair it´s definitely woth taking a shot. Now I have to put the stock tubes back in to see how they hold up.

Only today I received a JJ EC803S which I´ve been listening to for a while now. I´m curious because I heard praise for the ECC803S and that JJ is using the old Telefunken production machines. Sure it´s not broken in properly yet, but it sounds very nice already, less linear or analytical than the Telefunken it replaced. Let´s see how it will perform in the long run.

As you can tell, I´ve been tube rolling rather impulsively. I should sit down and take notes like I did in the beginning when I tried the first few 6SN7s and 12AX7/ECC83s. Now that the 300Bs and 805s are properly broken in it´s high time to roll back and compare. I can be more helpful for the discussion then.

Hey @chmaiwald , I've been there!  I had a Primaluna that could take a host of power tubes. I rolled, and rolled, and.... I got so lost but in the end I did figure out the takeaways. 

One thing that I learned was to listen to each tube swap and give them a fair chance.  It's easy to like something because it cost more or is highly reviewed. But everything is system, room, and listener dependent. I have a lot of 6 Cifte 12au7s (French military) that were very pricey--~$120 a tube.  They are amazing, yet in my system at that time I didn't need more air on top and things got to be too much.  Great tube to waken an overly warm or too thick tube system. 

I learned this again with my Manley Chinook phono stage.  There's nothing wrong (and soooo much right) with Electro Harmonix 6922s, which Manley uses in the stock units. For several years I neglected those tubes and created a stock pile of NOS stuff.  When I went back to the EHs a couple years later, I realized why Manley selected them--very quiet, full spectrum equality, and so on.

As to the Willsenton, my early opinion is the 300Bs are of great quality. They are drivers too so they aren't going to be as noticeable to most of us.  The 805s--I'm not sure on these. The Russian version of 6sn7 are good but pretty bright and highlight the midrange focus of the amp. In my system, they are a touch too much.  

So, the only current "roll" I have going on is Philco- Sylvania 6SN7GTBs.  They sound great!

Finally I found the time to do some tube rolling. It really started bugging me when I wrote recently that I didn´t properly compare the new ones I´m using with the stock tubes for example.

To cut a long story short: The tube combination I was running before still sounds best to my ears. Still some things I heard surprised me.

I listened to five tracks:
Bob Marley & The Wailers – „Natural Mystic“
Lee Morgan – „The Sidewinder“
Bastarda & Sutari – „Tam nad puszczaj“
Zbigniew Wodecki with Mitch & Mitch – „Wieczór już“
Phoenix – „Tonight“ (feat. Ezra Koenig)
I left out rock music because I wasn´t in the mood today. Also Guided by Voices, which I was tempted to include just to see how well a decidedly badly recorded piece of music is handled.

The source was my old Rotel RCD02 CD-player, I took the EQ out of the chain. Speakers as always Cornwall IVs.

805

Cossor – instruments more seperated than with others, sound a bit sharper (quicker transients it seems)
stock Willsenton (I think PSVane Hifi) – fuller sound, more bass boom (low end), overall nicer than Cossor
PSVane Acme – lush, general pleasant, round bass, coherent, voices glow

300B

stock Willsenton (I think PSVane Hifi) – slightly boomy and muddy compared to Elrog
Elrog – more presence and glow, overall just nicer

6SN7

PSVane CV–181 T2 – very good, but sounds maybe a bit too thick, less laid back, nice highs and lows
GE GTA (NOS) – deep low end, overall really good, not 100% clear, good presence in lower highs
6H8S (NOS) – relaxed, defined, maybe a bit generous with highs, beautiful but not very 3D
stock Willsenton (6H8S NOS) – coherent, lots of low end, very similar to other 6H8S
Sylvania GTB – relaxed but forward, sweet, I´m sticking with this for now, but GE and the 6H8S come close

Next up will be another round with the 12AX7/ECC83s, maybe the rectifier too, but I´m done for today.

Further observations:
– Replacing any tube makes a difference (rectifier the least). The overall sound did not change dramatically when changing the 805s and 300B, but enough to go from really good to great.
– Only the combination of the PSVane Acme 805s and Elrog 300Bs made the overall sound just sweet and glowing.
– I was surprised to find the Cossor least appealing of the three pairs I own. Surprised because I paid about $200 for them and they turned out to be less pleasant than the stock ones.
– No surprise concerning the 300Bs though. It would be really interesting to compare them with Western Electric and Takatsuki. Feel free to get in touch with me if you have a spare pair.
– The stock 6SN7s are also really convincing, better to my ears than the GE GTAs and the also pricey CV-191 T2 from PSVane. My first choice remain the Sylvania GTBs though, they do their job better overall. But just a bit so if they start failing at some point I won´t be desperate.
– I guess it´s because the Cornwall IVs lack a bit on the low end while overemphasizing the highs for my taste, but the sound is most pleasing when I put the EQ back in the chain and push the lows just a tiny bit. The other bands stay untouched, except for when I sometimes bring even the highs up a tiny bit. I know it sounds like a contradiction to what I wrote about before, but both help to make the sound fullest along the whole spectrum. The stage widens as well, it´s always a surprising effect, when I turn the EQ off and back on again.
– I still have to try other 6SN7 NOSs, if only they weren´t all so expensive.

@chmaiwald , GREAT write up. Thank you very much.  I know everything is system dependent and subjective but I'm going to pause on buying Cossair 300Bs based on what you say--may not be worth it.  

Also, fyi, I run two subs with CW IVs. You are correct in that CWIVs are not bass monsters despite their size.  I love the sound of two subs tailored into the lower octave only.  

Finally, I heard back from China Hifi today.  They said that 120ma is the maximum you should bias the amp. They have no recommendations on what's ideal. They said that 100 ma (where mine maxes out with full bias) is fine and you can go lower.  

As such, 120 ma is the limit.  Your mileage may vary, but you may want to turn your bias down from 120 to (a) see how it sounds) and (b) avoid running the power tubes so hot to save life.  

My Carver Crimson has a recommended top end bias of about 100 ma, but Bob Carver says he likes the sound best at around 80ma.  Interesting. 

At any rate, the manual uses ambiguous language and I have now confirmed that 120ma is not the recommended bias setting but the maximum bias setting a user should use. 

@jbhiller  Yes, I think you are saving money not buying the Cossors. And the PSVane Acme really shine but they do cost a lot. Luckily we won a court case this year about a faulty installation. It dragged on for years but in the end the decision was in our favour and the other side paid in time. Otherwise I would´ve had to save much longer for these and the even more expensive 300Bs. My limited experience now is in line with what I read elsewhere: The expensive ones do stand out. So far I have not read about a cheaper secret contender. That´s different from the 6SN7 and 12AX7 positions, where even I could name some that can make you very happy for cheap compared to the expensive holy grails of (usually) NOS tubes.

Thank you for passing on the info on biasing. That´s really helpful and I will try it out as soon as possible. I never bothered to try other values since I thought that 120ma is the only one I should aim for. Improving tube life and (possibly) the sound at the same time – irresistable.