Tube rolling experience in Aesthetix Callisto Sig

After a week with the Callisto Signature line stage, I was eager to hear the potential of this unit that Albert Porter has praised the last few years. As is quite evident, Albert has put much time and effort to get his Aesthetix units finely tuned with various NOS tubes and other wire and component updates.

After a brief review of his Audiogon writings and some recent email tips he sent me, I thought I’d try some of his ideas in my Callisto. His suggestions 2 years ago, when I got the Io, was to replace the stock Sovtek 12AX7’s with Telefunkens. The result of that was breathtaking in the improvements of bloom and decay. I did not update the EL34s in the Io’s power supply at that time as I was so content with the 12AX7s and I was pretty much out of money by then. But after tonight’s experiences with swapping the EL34’s in the Callisto, I will do this very soon for the Io.

Albert’s recommendations for the Callisto was to start with the EL34s in the PS. He wrote that this would be as dramatic as the Telefunkens in the Io. This is quite a bold statement but a statement that caught my attention. He then suggested trying a few different 6922s. I sensed that his advice to replace other tubes would be beneficial but only after the EL34s and 6922s were addressed first. I looked around Audiogon and hunted down various tubes recommended by Albert and managed to find a few sets to ultimately try in the Callisto.

The tube compliment in the Callisto is as follows:

Audio Chassis:

2 6SN7
4 6922
2 12AX7

Power Supply Chassis:

2 EL34
6 12AX7

The first tubes to arrive were a quad of Amperex 7308 (6922), a quad of Siemens 6922, and a pair of Sylvania 6SN7. The EL34’s that I was so eager to receive were still to come. Rather than wait for those, I went ahead and put in the quad of Siemens. Right away I could hear a ringing sound in the left channel when raising the level. Oh nuts, microphonics! I swapped the Siemens around to determine the troubling tube but now the ringing was gone. Perhaps a tube was not fully seated. Two nights later and still no ringing, so for now, this is not an issue.

I truly could not hear much of a difference with the Siemens vs. the Sovtek 6922’s. Late into the night I went back to the Sovtek 6922s and they sounded mighty fine but I detected a slight unnaturalness to the piano overtones that made them sound a little electronic. I then put in the Sylvania 6SN7 which brought on a very slight reduction in midrange forwardness. I put the Siemens back in and ran with the Sylvania tubes for two nights awaiting the EL34s.

Finally the Amperex-labeled EL34s arrived. I went back to all stock tubes and put the EL34s in the P.S. Oh my, oh my, I was so surprised and yet I was not. There was instantly so much grain removed. Vocals and piano came out from the fog! I had dynamics like not at all with the stock Electro Harmonix EL34s. I honestly do not remember differences at the frequency extremes as I was dumbfounded by how the mids were now so incredibly clear. What a wake-up call!

After 10 minutes or so I found the sound to be too fatiguing. The new EL34’s brought on so much energy but now there was a tonal imbalance with exaggerated midrange and ringing that was not at all to my liking. But remembering Albert’s comments that changes in some places would show “issues” elsewhere until they too were addressed, I kept a positive outlook on this adventure. I had detail with the Amperex EL34’s that I simply did not want to give back!

I had not tried the Amperex 7308 (6922) so they went in next. Yikes, lots and lots of midrange warmth. It was as if I put in a Cardas Golden Cross IC between the Callisto and CATs. Now there was even more tonal imbalance with too much midrange warmth. And there was even more of a sharpness to the initial strike of piano notes that had me running to cover my ears. I could see how this would be a good tube for overly dark systems but oh my not in the Callisto here anyway. A return to the Sovtek 6922’s took the sound in the right direction but now I was more aware of this initial-strike-of-the-notes problem. I did not have this problem with the stock EL34, or at least it was not so evident.

Next up was a return to the Siemens 6922. Wow! Now you’re talkin’. Piano now sounded much less electronic. There was space between the notes. Whereas the improvement of the Siemens over the Sovtek 6922 was subtle with the Electro Harmonix EL34s in the P.S., this difference was now a significant refinement with the Amperex EL34s in the P.S. The system now had detail in the mids that had only existed before in the trebles. But there was still a wee bit of a fatiguing nature to piano notes in the initial strike rather than in the overtones. This was almost like a sharp twang. It was not serious but still noticeable. And this was not a character I had noticed of the Callisto with the stock tubes. Clearly the Amperex EL34’s brought on much dynamic and authority characterizations, but they also unmasked remaining problems elsewhere.

So the Siemens 6922 was a huge step in the right direction with the Amperex EL34s in the P.S.

Remembering the subtle improvements of the Sylvania 6SN7 when using the stock EL34 tubes, I wasted no time putting in the Sylvanias. Big big smile! Once again, the subtle refinement heard with the stock EL34s was now huge with the Amperex EL34s in the PS.
The added presence from the initial strike of piano notes was nearly gone! It was so close. But there was no denying that it was an addition to the sound that was not there with the stock tubes. Other than this very minor issue, there was a wonderful tonal balance as with the stock tubes but now with much more resolution in the mids. The music had structure and definition and placement that was not at all present with the stock tubes. And finally I noticed a little more extension in the bass. Perhaps this was because the fatigue elsewhere was now gone.

So the Sylvania 6SN7 brought me even closer to tonal and musical nirvana.

With the piano now much more out in the open, occupying more of the presentation, I was wanting more body and dimensionality to the sound. The detail was there like never before but because of this detail, the volume of space of the piano notes was a little bit reduced and lacking in presence than I would have expected by this time. But I was clearly getting greedy.

With one pair of tubes still to play with, I put in the Telefunken 12AX7s. Initially I heard no difference. And still an hour into listening, I really could not hear a difference. Finally a return to the Sovtek 12AX7 and the annoying strike of the piano notes returned! As minimal as it was, it was clearly there! I had not even noticed it was gone with the Telefunken as I was so busy focusing on the bloom issue. But indeed, when I returned to the Sovtek 12AX7 I heard a reduction in the bloom of the piano as well. It was not so easy to hear this improvement with the “step up” to the Telefunken, but a return to the Sovtek and the difference was immediate.

So the Telefunken 12AX7 not only removed another layer of the Sovtek fatigue but also brought on a little more dimensionality that I wanted.

Now I have a huge improvement in musicality like I simply could not have imagined from the replacement 10 tubes. I would be very surprised if the second P.S. would bring on the dramatic improvement in dynamics and resolution like this tube update has done.

So what did I learn here:

1) Albert was absolutely right on when he said the EL34 tubes would be THE significant change here.
2) No matter what type of tube it is, i.e., 6922, 12AX7, 6SN7, Sovtek tubes absolutely have a house sound. There is a definite fatigue in the initial attack as well as overtones in a highly resolving situation. And these tubes are not very high in terms of resolution.
3) Unless you can also replace ALL of the Sovteks tubes in the audio chassis, I do NOT recommend changing the EL34’s. The EL34 change not only brought out more of the potential of the Callisto but also brought right to the forefront the additive weakness of all the Sovtek tubes. And the result was a step in the wrong direction until corrected by changing the other audio chassis tubes.
4) There is little gained by replacing the tubes in the audio chassis as the refinements brought on by the tubes here will be masked by the mediocre dynamics and resolution capabilities of the stock (Electro Harmonix) EL 34 tubes in the P.S. Again, Albert was right: there is a definite pecking order.
5) There is much to be said about a matched set of tubes for any given product. Just throwing around NOS tubes and expecting magic to immediately happen will only result in immediate frustration.

With the audio chassis now retubed with non-stock tubes to match so well with the EL34’s, I can put the cover back on the audio chassis and not worry another minute on this for quite some time. Perhaps the replacement of the six 12AX7 tubes in the P.S will bring on some benefit, but for now, I am very pleased with the outcome.

This “updated” Callisto has all the dimensionality of before but now with dynamics and detail that would knock the socks off anyone, including JD. 8-)

A note to Guido: I think I finally found that Bosendorfer.

And Albert, I now owe you 2 deluxe strawberry cheesecakes.

John