From my audio log:
"When I got Io back from repair in 2017, it came with a full new tube set that I ordered from the factory.
Earlier, I had used NOS tubes in the most important positions (V1-2), but these had become noisy.
The new tube set from Aesthetix used new JJ signal tubes for positions v1-v6.
I had used Telefunken NOS in V1-2.
I quickly realised that the new JJ tubes were indeed very low noise. Plus one to Aesthetix - these were clearly selected for low noise.
Yet they weren't as musical as the Telefunkens.
So what to do.
I first reinstalled the Teles in v1-2. Living with the larger background noise. Then I got tired of it.
I invested in four Philips Herleens for v1-2, and have not looked back. Or: not so much.
The Teles may be slightly better overall, but the Herleen have a bit of "rock foot", and both are above the JJs (and Sovteks) in musicality.
So, since the Herleens are low noise (even if not quite down to the selected JJ low), I don't regret. Also, since the Teles - real low noise - are now very hard to get.
Since the Philips Herleen NOS worked well in v1-2, I also ordered Herleen 6922 in V7, and RCA NOS 6sn7 in v8 (heerlen E88CC and RCA 6SN7GTB).
These have now replaced the ones in the tube set from Aesthetix in 2017 (v7 - Electro Harmonix, v8 Russian 6HA7).
This is where the jury is out to lunch, - a rather good and extended lunch, I would say.
Does it sound better? I wish I could invite you over, to listen.
It is maybe a bit leaner and also purer than I got from the Electro Harmonix plus Russian v7-8 combo. I associate Electro H with rather limited sound, but the Russian is really a contender
from way back when, and was included in the Io tube set for a reason, I believe. However my experience with RCA output tubes are generally good, so maybe this will come to the forefront, here also.
The NOS tubes are possibly unused, and need run-in.
For reference, the tubes I try in v7 and v8 now, are Philips Herleen 6922/e88cc and Rca6sn7gtb)."
My impression from reading Albert Porter's very valuable advice, years ago, was that the best idea was to move from v1 to v2 and so on downwards (from his "long" post, not reproduced above).
First, get the Io to sing in terms of the input from the cartridge. Then, change tubes downwards in the chain. Be aware that upstream and downstream tubes tend to go together differently, some match well, some dont. So he gave quite complex advice. I don't know why, exactly, but it seems that he later changed to an Allnic phono pre.
My general impression is, even if Philips tubes from the Herleen factory aren't quite up to Telefunken standard, they are very good, and clearly above new production including Psvane, Sovtek, JJ and china (where I have tried them).
They do well in the v1-2 position - low noise, and more musical than the factory-supplied JJs.
Also, I think, in v7. I am not sure, however, if this is better than with the factory-supplied EH and russian 6ha7 in v7-v8. A bit better, clearer - maybe.
Some have associated RCA with "mud", but the impression here (v8), rather, is a more "slim" sound. I use RCA NOS in various positions, and don't agree that they generally sound muddy.
Sorry for not being more precise, but in my rack, I cannot do easy AB-testing.