Tubes preamp variety
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Yeah, but it's also ubiquitous, and there weren't a lot of other high-gain dual triodes.
These guys have a good selection. I can't find it on their site now, but I believe they will match tubes, though I can't imagine why you'd need to with the 12AX7. Far more important to match output tubes in class AB.
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9,909 Posts
It's in a DAC where it'll be used as a cathode follower as there's no need for gain. There are still much better tube available such as the 6DJ8 or 6H30 for this role. Tubes in DACs are a gimmick and the 12AX7 chosen because it's widely available, cheap and has a low plate current which reduces PSU costs.
Seldom even worth doing there. Matching is typically only done at one plate voltage and current, not much use when the loadline is across the entire width of the characteristic curves and with the reactive load of most speakers, it's a very fat line.
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Ok the reason I mentioned for use in a d to a converter was the fact that a lot of sovteks fail in a very short time. Last time I bought this type tube. (Cable Company) they sent me amprex they stated in this application they would be a good choice & be durable, which they were . The unit came with unmarked Chinese tubes
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Thanks
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9,909 Posts
Not in my experience. EH and Sovteks were my standard replacements when servicing guitar amps and vintage audio unless the person requested something specific.
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65 Posts
Those old tubes are indeed more durable--plenty of audio buddies of mine have replaced the import tubes either due to early failures or, they just sound like crap. I have a small amp here that came with three of those no-name chinese tubes, and after about an hour at temperature they start to smear the highs. Drop in some vintage new old stock Mullards and it's a completely different amp.
Check out the tubes over at Upscale Audio--the prices are a bit high, but at least the owner has heard these tubes, and there are user comments as well. (If anything, it's a good place to window shop.)
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1,038 Posts
Could you explain in detail why you think 12AX7 is the worst tube used in audio?
High output impedance and distortion?? How about 5751??
Not trying to start a war here, just trying to learn more about tubes as I just recently got into the world of tube sounds..
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9,909 Posts
Plus high noise, and too much gain for most applications.
Marginally better.
No, it's a fair question and whilst I think tubes are by and large a waste of time for audio, I would encourage strongly trying to understand the engineering behind tubes and why circuits are designed as they are. Better tube and topology choices at the design stage will make a far, far greater difference than tube rolling. Morgan Jones' Valve Amplifiers is a must buy as is Building Valve Amplifiers. He explains design choices very well in the examples in VA as well as a bajillion other useful things for the novice to know.
Just because you play with evacuated glass bottles, don't be a Luddite and use SS in companionship. Regulators, constant current sources and rectifiers are much better in SS, easy, cheap and small and work better in most instances than a glass implementation. Some hybrids are spectacular.
When you know more, start reading John Broskies Tubecad blog. There's about 16 years of very well written and thought out articles, innovating and explaining like few ever have.
... or ECC83, IIRC?
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9,909 Posts
It's a 12AX7. English nomenclature.
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Upscale Audio offers new high-quality low-noise russian-made Mullard branded 12AX7s for only $24.95 each and will match pairs at no charge.
They also have 10 or so other 12AX7 choices available.
Anyone that says the 12AX7 is a low-quality tube is extremely uninformed. When used in well-designed circuits, it will give excellent performance.
Understanding its characteristics and designing the circuit well is critical.
One of the best preamps I ever had, the Harman-Kardon Citation, used several of them and it was excellent.
The 6DJ8 and 6H30 are unquestionably lower-noise tubes, however.
The 6H30 is the best there is for premium preamp designs, and is used in the Audio Research and other SOTA preamps.
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