I haven't used either tube, but am familiar with their reputations, especially the CCa.  But my experience with 6922/E88CC tubes (like the CCa) has not been good on my UFO25. They were some of my favorite input tubes on my UFOs, but for whatever reason I haven't had good results with them on the 25s. PCC88s match much better for me, and in your position would consider the Lorenz before the Siemens.  FWIW €200 seems like a lot for the PCC88, but maybe that is where the market is these days.

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Yes . I have the other 3 and like them a lot. The Mullard is on the warm side with more emphasis on the low frequencies. The TFK is my favorite, super transparent and linear from top to bottom. The Philips is in between, a little warmer than TFK and a little more linear than the Mullard. I would get them all, then report back on what you think.

Ok. Tubes arrived earlier today and popped in the Telefunken PCC88 first based on your description, CAJames, and to be perfectly honest I'm a little in shock.

There is a considerable sonic improvement compared to the stock tube from Decware. It's like I'm actually getting that "holographic" sound that people always bang on about. Part of me wants to attribute it to "new gear syndrome" but I mean everything sounds fantastic so it's difficult to deny that something is going on. This is the first time I've rolled an input tube on my UFO25 and frankly I'm surprised to see it make such a difference. These PCC88s are a bit of a revelation it seems.

Curious to try out one of the other three tubes but I'm enjoying this TF (paired with a RCA Globe Type 80 and Cryotone EL84s) so much that I may just stick with it for now. Why ruin a good thing? Haha

It's funny that you mention the bias switch. I've been going through a bit of a crisis of faith with it recently haha. Since getting the amp a few months ago (and also with my previous UFO2.1) I always preferred it set to the Low position. However I recently removed the isolation feet from my speakers (Omega Junior 8 XRS) due to WAF and it's like everything significantly dipped in volume as a result.

So, rather than just turning up the volume (which I tried but found that I needed to push it much higher than I liked) I flipped the bias switch to High and found that it improved things significantly - more punch, dynamics and presence in the music. No matter what tubes I rolled it didn't make a difference. I also thought it perhaps might have something to do with the amp seasoning but that seems a little implausible as it's not something I ever experience faith my UFO2.1.

I'm surprised that the isolation feet really made such a difference in this situation. In fact, I have a different, more discrete, set arriving next week and am curious to see what result it will have.

Btw, and please excuse my ignorance, but is it the input tube that most affects the bias switch on the amp? Or is it any tube?

Just to follow up on what Lon said, when you change the height of your speakers you also change the frequency response at your listening position. The volume may be a little lower as well, but I think it mostly "sounds" lower because you are hearing a different mix of high/mid/low frequencies, and I suspect you are getting less bass then you were with the footers. You kind of proved that by turning up the volume but not liking the sound. So when you flipped the bias switch you also changed the frequency response of the input tube, probably in a way that compensated for the change in your speaker placement.

Thanks gents. Of course the height of the speaker would affect volume, can't believe I didn't think of that! Will be interesting to see when these new footers come in next week if things will go back to how they used to be. Not sure of they're the same height as the ones the boss disapproved of, but I imagine they're still taller than the stock Omega spikes (which do in fact look lovely but I feel just don't gel with my suspended wooden floor very well).

Thanks for the tip on the Tesla E88CC - I see there someone here in Norway selling a matched pair for ~160€. Not sure if that's a fair price? Might be a little rich for my wallet right now after having just spent a tidy sum on all those PCC88s...

Just for fun I rolled in my EL822s to replace to see how they managed with the TF PCC88. Sounds decent but isn't wowing me quite as much as the Cryotone EL84s did. I'll give it an couple more sides and switch back I reckon. Tube rolling is fun but boy is it like a neverending multiverse of possibilities.

Guys,

Are the Tesla E88CCs yellow or white label? Or both (either)?

So I went shopping and picked up a pair of Siemens labeled Telefunken PCC88s (TFK made tubes usually have a raised diamond mark on the base, "mit <>") for a pretty decent price (by 2024 standards). If\t took awhile for them to breakin, a long while actually, but now they are sounding really good. Exactly what you'd expect for the typical "German" sound: transparent, dynamic and linear. Some people might say they lack tube warmth, and to them I say to each their own.