First post here but wow! Those are massive beasts! Look forward to seeing how you will incorporate them into the circuit.
I have now officially read this entire thread over the past couple of weeks and thought I would join the conversation.
I have had my R8 for about two weeks now. Bought it second hand from eBay for a great price. It came with the stock Willsenton El34 set except in the 6sl7 position that had new Tung Sol.
At first I had some issues that I had trouble tracking down. Apparently the seller had been running KT88 and then swapped back to EL34 mode, put the tubes back in but did not re-bias for EL34. I stupidly did not immediately check the bias with my bias meter but noticed that according to the internal bias meter that they were biased pretty hot! So hot that that evening when the lights were lower I noticed that one of the tubes was red plating. At that point I shut the amp down turned bias all the way down and got out my Weber bias rite meter. Checked bias got everything back to a normal range and did some listening over the weekend.
I was less than thrilled with the sound going to my Wharfedale Linton's. Seemed incoherent, shrill, etc. I was undeterred and prepared for this and began the tube rolling shenanigans.
I ordered a set of new Tung Sol EL34B from Tubedepot.com along with a set of Nos Sylvania 6SL7GT. I also ordered a single NOS RCA 6SN7 for the voltage regulator position. Experience tells me that even though that tube is not in the signal path I might get more consistent voltage feeding the other tubes.
Started with the Sylvania tubes. Sounding much better than the current Tung Sol, unfortunately had some audible hiss from one of those so back they went and put the TS 6SL7 back in. Luckily Tubedepot responded quickly and made it right with zero questions or fuss. They are great to work with.
Next put in the Tung Sol EL34B and biased with the Bias Rite. Sound was noticeably better. Warmer, more coherent, sound stage that made sense, etc. At that point I left it alone and was trying to enjoy the music. Something still seemed off though.
After a couple of days I noticed that the screen print logo on V1 and V4 of the TS EL34 had darkened noticeably. Uh oh. Knew something was amiss. I was already suspicious that my Bias Rite was not giving good readings and it turns out that one of the two probes was reading about 20 mA too low. I suspected that the other was working properly so I rebiased all tubes using the single probe to about 34mA. And there it was the famous tube imaging and soundstage locked in. Go figure lol.
I also ordered one of those Nobsound testers from Amazon to use as a confirmation that the one probe of the Bias Rite was working as expected and it was. I have to say though that my meter readings on the internal bias meter are fairly different than other folks here. I definitely don't trust that meter.
I have been listening as is for the past week and a half and am enjoying the sound but it is still a little bit brash in the highs with my speakers and large open room with high ceilings and wood floors. Not an ideal listening environment but it can sound good with the right system.
I currently have more tubes otw. Some Melz 6H9C metal base along with some other Russian cheaper 6sl7 and 6sn7 variants. Also going to be checking out some NOS american 6SN7 and 6SL7 that will be sent as part of the exchange for the bad Sylvania tubes. Took a swing on some JJ 6CA7 since they are so cheap and are reported to be a little darker sounding.
Lastly I've ordered parts to try some of the @Fruit mods. Have some Russian PIO caps for the bypass. Haven't ordered new filter caps yet but that is high on my list. Couldn't believe the stock were only rated at 450V. My plate voltages hover between 448-452 so plan to do that quickly.
I'm definitely not an expert, but I do love rebuilding, tweaking, etc audio equipment. For the price paid I have no hesitation about modifying this amp. It will be incredibly easy to work on as well, just wish there were a true schematic.
Apologies for the long first post but happy to be here.