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Greetings, TA. This is my first post, so apologies in advance if a similar thread already exists (I could not find one via quick search)...
I just broke my piggy bank on a Schiit Mjolnir 2 "tube hybrid" headphone amp. To its single-stage analogue (RCA) inputs I've connected a turntable by way of a Bellari VC-130 single-tube phono preamp (the Mjolnir does not include a separate phono stage). So far they seem to coexist nicely, but I want to replace the stock tubes in the Mjolnir with some different (older) makes. So I'm wondering how important is it --- sonically and/or electrically --- that the single 12AX7 tube in the Bellari match up with the two 6922 tubes in the Mjolnir 2? Or should I not worry about any cumulatively negative effect from using completely different tube brands/years in each of the two preamps? If / when possible, any feedback or suggestions from the TA veterans out there would be appreciated!
I don't know the architecture of the Schiit, but if they are the main source of amplification, which is not unusual in a headphone amp, then they should be matched.
I forgot to mention that this site had some really good private sellers of used tubes. I think you should take a look, I have been pleasantly surprised. However let me reiterate that the 6922 was not made in the kind of quantities that the 12A_7s were, or so I am told. Sadly not a lot of current manufacturers use 6DJ8s which are more abundant.
Thanks, Mechans, for your further thoughts. According to Schiit, the Mjolnir II accepts both 6992 *and* 6DJ8s. They also indicate that the stock tubes can be swapped out "for anything in the 6DJ8, 6922, ECC88, and 2492 families," so hopefully that will broaden my choices. Right now I have installed Schiit's (stock) 6BZ7 tubes, which sound decent enough. But I have not yet compared them to anything else. But I'm still wondering, are the differences between the 6BZ7, 6DJ8, 6922, ECC88, and 2492 tube families merely formal/superficial, i.e. simply a difference of name/description? Or are there important structural differences between them which, while potentially significant sonically, nonetheless allow them to be completely interchangeable in an amp like the Mjolnir II?
I don't have any experience with the 6BZ7. It's name congers up an octal but obviously isn't one. Will you hear a difference if you roll the tubes? I certainly do in many cases, but not all circuits really permit that. Have you tried rolling some other tubes in other gear? what's been your experience with that? None of that tube family is warm IMHO, but try to get some used Mullard/Philips 6DJ8s, you might them.
No, I have not yet tried any different tube types in either my Bellari (phono stage) or the Schiit Mjolnir II, so I really can't be certain that my ears will hear whatever differences do exist, esp. if there is some other part of my audio gear that is weaker than needed to take full advantage of tube differences. But I am anxious to try out a Mullard -- such as the Philips 6DJ8 you mentioned -- as soon as the opportunity presents itself, and will report on the results (for whomever that might be of interest). Thanks again, Mechans, for your suggestions in that regard!
The 6922s are not easy to find at a low price, I am afraid a real world pick would not fit into your budget.
If you want to damn the torpedoes, then look for white label USA Amperex some are designated E88CC, another fine tube is the Siemens 6922. Mullard made several styles of the 6922ranging in warmth knowing that most 6922s are not really warm, to sparkling. The tube I use is the CV-2493, Upscale Audio once carried them, they are not a budget tube.
There is an old FAQ on 12AX7s you should be able to find on this site. It concluded that 5751s were the way to go, but for a Phono pre it's probably not because of the reduced gain. Old stock Mullards are warm for the most part esp. 1950s long plate Blackburns. Philips also made Amperex, Valvo and Miniwatt. Your best buy for a British tube might be Brimar.
Thanks, Mechans, for those very helpful suggestions. I'm prepared to spend more on a tube if / when I can be fairly certain that the upgrade is sonically evident to my own ears, but I'm certainly not willing (or able) to spend hundreds of dollars on a single tube if the improvement is less than staggering. From what I can see on ebay and various online vendors (via Google searching), tube prices are all over the map, and the variety of types & brands & years & other production details are simply overwhelming. But at some point I definitely would like to try out one of the British makes you mentioned (Mullard or Brimar), so thanks again for those suggestions. And I will also search the site for the FAQ thread on 12AX7s you cited.
Thanks very much to all who responded to my post. Glad to know that mixing tubes across pre-amps should be fine.
Yes, dirtyvinyl, I, too, would be interested in hearing a critique of the traditional presumption about matched tubes, so please do post a message to that effect if / when you recall where you read it. I'm still only just begun to *try* to explore the physics of vacuum tubes, but from what I've read and seen online, there does seem to be a consensus about the importance of "matching" tubes.
So if I understand your post, Interstage Tranny, it sounds like the different tube types might actually be better (although I don't know, technically speaking, why that may be). And *thanks* kindly for your detailed suggestions about tube choices. Thus far I've been relying on the stock tubes in both the Bellari and the Schiit Mjolnir, but I already ordered a Russian "Groove tube" for the Bellari and a pair of Russian 6N23P-EV NOS tubes for the Mjolnir. All were fairly inexpensive ($20 for the Groove tube, $30 each for the two 6N23P-EV), but hopefully they will begin to give me an idea of sonic differences across tube brands. In any case, I will be sure eventually to try some of the other tubes in that price range which you suggested (Telefunken, Sovtek etc.). As you noted (wisely, I'm sure), I think I first need to see if I can even discern any significant improvements from one brand to another. My ears are not young and may have already deteriorated to the point where difference among tubes may not be as perceptible as they should. That said, thus far I'm *really* enjoying the sounds coming out of this Schitt Mjolnir hybrid headphone amp, and, of course, I would like to get the best sounds out of it that are financially feasible...
Thanks again, and I will definitely follow up if & when I have some post-worthy observations about the new tubes in my (sonic) life.
If you are worried about cumulative effects, choosing different brands with different construction internally will avoid any inherent distortion products from being additive. Since these two tube types usually differ in construction, it is probably not a concern.
You don't mention the current types installed or factory types either. I know folks who enjoy the genuine Sovtek 12AX7 LPS for their Bellari. If the 6922 tubes are Chinese, Russian or American, you might try some UK, Germany or Holland sourced vintage types. Do not be afraid to buy good used tubes, if they are guaranteed to please by the seller, or the bay.
Only you can decide which tubes are best for your applications and fave music. It really does not matter what tubes anyone recommends. It is your happiness and enjoyment at stake.
Consider value versus cost, at first. For example, the "classic" vintage fave was the Telefunken ECC83/12AX7, either early "ribbed plates" or "smooth plates" types. Beware of the non-genuine smooth plates, which lack the pressed in glass, diamond and date codes on the bottom of the tube between the pins. These later "copies" do not have the same quality. Anyway, at $40. or more per good, used Telee tube, the Sovtek LPS can be procured and guaranteed for under $12. each. Will you enjoy the Telee that much more ? It is only a possibility...but, perhaps...Then again, maybe you will prefer the Great Britain or Holland made "small plate" types of classic 12AX7/ECC83 which can be bought for around $30. each these days. There are lots of golden oldie and newly made types to consider.
Now, the 6922 family have many more modern and vintage choices due to the possibility of using 6DJ8/ECC88, 7DJ8/PCC88, 7308, then the various manufacturers and types of each through the years.
While some of us treasure the sound of the earliest versions of both tube types of concern here, your craving may differ. That is why I say to start out "easy" and make sure you can discern the sonic differences, which can then influence your possible splurging in the future.
When you have some subjective thoughts on differences, by posting again later, there are some wizards and distributors on board here who will jump in and recommend more, based on your subjective observations.
Enjoy the audio journeys...
Someone may respond with a more technical explanation but..
Typically, reserved for power tubes without bias adjustment for each individual tube.
I even read somewhere years ago, an engineer/designer questions the validity of "matched" tubes and how flawed the idea is.
I wish I had a copy of that article. Probably would provoke interesting responses.
Diversity is good.
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