Hi, Hope you don't mind me commenting, , as I'm not a Rhea owner, although I have read virtually every archived post present here about the Rhea, as at one time I had thought of purchasing one. I ultimately went with the Sutherland PhD instead.
Seems many have had Tube issues with this Unit, with Tube noise, noise, etc, and it made me reluctant to worry about rolling tubes, and the expense of tube rolling-experimentation to get a proper satisfactory combination.
Also don't profess to be any valve-tube expert, but from what I can gather from your post, V1 through V4 all use 12AX7 Tubes, correct? (I'll leave others to comment if other Tubes-Variants such as he 5751-CV4003 can be used.)
I'd gather that a tube with low noise, low microphonics are paramount to the best operation in the Rhea, and it is my thinking that a well built Tube with triple Mica spacers may offer better performance with lower noise- microphonics?
Perhaps give the "lowly" Shuguang 12AX7 C-9 production try? These are nicely made triple mica blackplate tubes (with halo getter), and appear to be a very decent tube, especially considering a quantity of 4 will run you about $24.
I'm not sure just how important tube matching is with the Rhea (I gather it is), and I believe there are those out there who could match these (or even Cyro if you desire) for a minimal fee.
Might be worth a try for the small outlay of cash before you indulge in the 'Funkens, Amperex, and the like? Hope this helps, Mark
The most important characteristic about the tubes used in V1 and V2 is that they must be very quiet. The Rhea is inherently noisy and putting noisy tubes in v1 and v2 will make it much more so.
To each his own, but I found that in the end the best overall sound with the Rhea was achieved using the stock tubes. Everything else I tried either rolled off the highs or the lows.
Try a search on "Rhea". I know there is a thread in the archives on rolling tubes in the Rhea.
Best of luck,
I've also heard on noise issues with Aesthetix Saturn Series units. From everything I've read, I'd agree with Dan_ed, use the Aesthetix stock tubes in the 12AX7 positions. The Aesthetix can sound very good, but is picky with tubes. Some have had success rolling the 6922's in the Calypso, but recommend staying with the stock 12ax7's.
Here are comments from Jim White of Aesthetix regarding the 12ax7's in the Calypso, thanks to Jadem6's review of the Calypso on AudiogoN:
I emailed a draft of this review to the distributor who in turn forwarded it on the Aesthetix. Lucky for all of us, the president and founder of Aesthetix took the time to help us learn how the tube problem arose, how they solved it and the enormous quality control they employ at the factory. Please take the time to read his response.
Dear Mr. MacRae,
Thank you for the detailed and insightful review of the Calypso, and your tremendous patience!
Regarding the tubes, a bit of history:
I originally designed the Io around the Sovtek 12AX7WA, then went to the 12AX7WB when it came out, because I thought they sounded better. For many years, the Io was sold that way, with very few problems with the 12AX7WB. When I set out to design the Calypso, I based its gain stage around the same tube, based on that past successful experience. The operating conditions are identical to that used in the Io (plate voltage, plate current, etc.) For about the first 6-8 months of production, we had almost no tube problems with the Calypso. Then, they started cropping up, as noise like you encountered. This was our worst nightmare, because we thoroughly evaluated the units before they shipped. They were going noisy after leaving our facility. We immediately started burning the tubes in longer and testing more thoroughly and stringently, but with little success. I looked into alternatives, but no tubes of current manufacture worked properly or to my satisfaction, so we stayed with the Sovteks and continued trying to find ways of culling tubes that would go noisy. Near the end of last year, we finally found a 12AX7 of current manufacture that sounded good and would remain noise free. We have since switched to that tube (Teslov E83CCS), and our tube noise issues have been drastically reduced.
Every tube that we use is tested. First we test them at the same operating conditions that they will be used in our units, and write down the pertinent characteristics. Then, we go through and match the tubes for gain and other parameters. They are then installed in production units and again tested for noise, matched gain and other operating characteristics. Next, the units are burned in for 100 hours and we evaluate the noise a few times during this period. Then there is a final listening evaluation that includes noise testing. The same basic procedure is used if we are replacing tubes in the field.
One aspect of all of my designs that contributes to more demands on the tubes is that I do not use any form of global negative feedback, as I believe it is damaging to sound quality. Feedback greatly reduces noise, distortion, tube matching requirements and output impedance. If the Calypso had global feedback, many of these tube problems would not have exhibited themselves. It is my decision that it is worth the pain and trouble to test and match tubes to achieve the sound quality described in your review.
As you wrote, the Calypso is a simple circuit. It basically consists of input switching, volume control, gain stage (12AX7), output stage (6922). Therefore, anything that happens in the 12AX7 goes directly to the power amp and will be heard.
Thank you again for your wonderful review, I enjoyed reading it.
Thanks to everyone for their input.
I rolled all the 12ax7s (v1-v4)with Brimar CV4004s and started getting what sounded like feedback from the speakers. I then switched v1&v2 back to stock and that worked out well. The sound is different to be sure. Most Lps sound better but I'm not so sure about a few. I'm assuming I have to give the tubes some breakin time so the sound should open up a little more.
I may also roll the 12ax7's in the Calypso to see if that makes a difference since it seems the CV4004 matches well to the 12ax7wb. From what I have been able to research the 12ax7wb is simply a higher quality 12ax7wa. I can't seem to find old 12ax7wb's. Is it is a modern tube variant of the 12ax7?
As for v1&v2, I'm not optimistic about finding good replacements. I need to find 12ax7lp's. I'm assuming that lp stands for long plate. I've seen Mullard long plates but am wondering if there are other options. I'm guessing these have to be very well matched.
I'm also curious what Rhea owners do when their tubes start to pop after warranty is up. Can you order a new set of stock tubes from Aesthetix?
I'm under the impression that yes, Tubes can be gotten directly from Aesthetix for your Rhea, and this in many ways may be the best, and easiest plan of attack for yourself.
They'll no doubt know exactly what works best with thier units, and ease the difficulty, and expense, and time of rolling NOS Tubes.
I would imagine matching does become critical with NOS Tubes, as one "assumes" the Tubes one is getting are fresh, without countless hours apon them.
With brand new fresh tubes, I'm not then so sure just how important matching is, and I'm doubting channel imbalance would then be an audible problem?
Again, I'm no expert, and welcome oter's comments about just how critical matching is with brand new fresh tubes? I also assume the most critical matching in the world will not in any way mean that a particular tube is going to be compatible, nor will guarantee that said tube is a quiet, and a good sounding tube. Mark