Have had best SQ using 807 tubes.
Tried EL34 and did not like any. I have a bunch of 6L6, 6V6, and 6P3S-E / 5881 / 6L6GC. I am very curious if these would work, it’s an excellent tube and possibly hidden gem in its performance based on how good it works on different amp I have that’s actually specked for it…

Currently running KT66 and all seems fine along with great sound quality and character.

A friend of mine let me check out his McIntosh MC60, which he had recently purchased on ebay. He's a rookie in stereo equipment, and when I told him that he had bought a mono-block, he was a bit disappointed that he would have to find another one for a full stereo setup.  But I told him I would be glad to check it out, to make sure everything worked.

This amp came stock with it's original tubes, KT88s and I believe they are original General Electric...couldn't really tell though as the labels were rubbed away, or what was a sticker was gone. But they were not reproduction tubes.  In fact all the tubes, were original.  Telefunken 12AX7s, GE 5U4G ...just amazing.  Nevertheless, I thought it would be fun to try the KT88s on the Rachel, to see if they had life in them and what the sound would be.

At first it took a little bit of time to let them come up to current, but they made it to 40mA, except for one tube seemed to have a bit of an issue.  Some gentle taps and movement in the base seemed to do the trick and she was up to 40mA.

I then put on some music, XTC's Ball and Chain 45rmp 12", and what I was treated to was a very detailed high end, and lows...well it seemed somewhat revealing.  I could hear the skin and air of the kick drum and it's resonance, was one of my initial impressions.  The highs were silky...I was just in awe of what I was hearing.   Non-fatiguing sound as I just didn't want to turn off the system ( had to as I had "responsibilities").  Everything I listened to, from CDs to vinyl just seemed to really come to life.

This tube replaced a pair of Seimens GrooveTube EL34s that I've had since the late 80s that were originally used on my Marshall amp. But that's one set of the many tubes I've put into the Rachel.   I have tried 807s, 6L6s, KT77s and various brands of EL34s.  All have their own characteristics and quite good and pleasing, but these KT88s made me hear something different than those other tubes.

All I got to say is that I really don't want to give these tubes back to my friend, but will have to soon...but in the meantime, these KT-88s seem to be my favorites.
I'm looking at prices for replacements.  Originals are totally out of my price range at this time, so I see there's Gold Lions out there, which I think I could swing...but these are not NOS so I'm not really sure if I should take the plunge.

I've had my Rachael for almost a year now and it is connected to Forte 1 speakers with Crites crossover and tweeter upgrades.

In this time I have rolled the following tubes:

Power:  NOS (New Old Stock) RuMil 6N1P-EV and NOS JAN (Joint Army Navy) Phillips ECG 6922 (NOS RuMil 6N2P-EV on the way).

Rectifier: Nesstone 5U4G, Telefunken GZ34, JJ GZ34S/5AR4, Philips JAN 5U4GB, PSVANE 5AR4.

Output: Decware EL34, Nesstone EL34, TungSol EL34B, Shunguang EL34B, JJ EL34-II, JJ EL34L, new prod Mullard EL34 (Electro Harmonix 6CA7 Fat Bottle & Preferred Series 6CA7 on the way)

On the Power Tubes I frankly heard no obvious difference between the 6N1P and 6922.  Will see if the 6N2P-EV mades an audible difference.  Anyway, with 3 sets of Military NOS power tubes I should be set for life.

With the Rectifiers the Telefunken was obviously more dynamic and punchy than the Nesstone. I liked it much more so kept it in for a long time.  When I tried the NOS JAN Philips 5U4GB I was quite surprised of the tonal difference it imparted. Mids were noticeably more richly tonal as well as have a smooth liquid nature to them.  The PSVANE was also quite nice and very close to the Philips JAN tubes being just a little less tonal on the mids and a little less liquid. Still far nicer though than the Nesstone or Telefunken. The Philips NOS JANs are fairly easy to find and in same price category as the PSVANE and given their military hardening should last quite long I am hoping. Would recommend either the PSVANE or the NOS JAN Phillips.

On the EL34s, the Nesstones were fairly flat sounding and the Decwares more relaxed than I prefer.  The Tung Sols were somewhat dark. The JJ EL34-IIs and Mullard EL34s were nicely dynamic with excellent bass and good all arounders. The JJ EL34Ls were very dynamic, much more so than any of the others and bass punchy and tight, so just outstanding. I like the Mullards and JJ EL34-IIs a lot and find them great across generas.  The JJ EL34Ls though are really something special and can really rock!  So I switch back and forth between these depending on my mood.  I am quite looking forward though to trying the Electro Harmonix 6CA7 fat bottles and supposed to be quite similar to the NOS GE 6CA7 Fat Boys (which I may eventually try but expensive usually being $150 each).

So in sum my favs of all these are the 6N1P-EV or Philips JAN 6922s, no preference.  For the rectifier the Philips NOS JAN 5U4GB PSVANE 5AR4.  Finally for EL34s the JJ EL34-L and then either the Mullard new production or JJ EL34-IIs when I want a less punchy/dynamic presentation.

Overall am finding the Rachael a thoroughly wonderful unit with plenty of power for my Forte 1s or Tekton Lores or Omega SAMs.  Tube rolling has been fun and not too expensive given just 2 EL34s and showing nice alteration of the sound signature so can tweak it to preferences.