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I have a DAC with a tube output. It was originally designed for 6922's. Not being a big fan of the 6DJ8 "family" and seeing 6922/6SN7 adapters, I thought "why not?".
Then I looked at the 600ma filament current, which led me to the 6SL7. They sound excellent, but I'm concerned about the difference in grid resistance and longevity. I was told to check the voltage at the tube side of the output cap, and that 100v (+/-10%) and I would be "good to go" (measured voltage is 102.3v).
Any thoughts or suggestions would be appreciated.
Rikkitik, what is it about the 6DJ8 or the 6922 that you are not fond of?
Not asking to be confrontational--just curious.
I guess the biggest failing (for me) would be my difficulty in finding one that "does it all". IME, certain Amperex have very nice mids, but weak/rolled off bass. Siemens (Germany) have nice extended (though somewhat "bright) top end, decent bottom, ok mids. Old Tesla "32's" have nice bass, mediocre in the remainder of the spectrum. Those are just a few of what I've tried, but it kind of makes my point.
Plus, due to their popularity (6DJ8/6922 family) there's tons of counterfeits on the market to hopefully avoid. The '75 Reflektors are the closest I've found, but lots of those are counterfeit as well.
I've never heard old Tele's, for the same reason I've never heard TS BGRP 6SN7's, they are so expensive and hard to come by, why go there. It seemed like 6SL7's might be a way to go.
But as others have mentioned, 6SL7's are not the "drop-ins" I had hoped. They do actually work and sound great, to an extent. Their gain is fine, but voltage swings on peaks are exaggerated and harsh.
I intend to look further into circuit mods/adaptation, but that may be a dead end street.
Maybe give the JJ gold pin E88CC a try if you haven't. Selected for low noise/microphonics they're @ $30 a piece. I like them every bit as much as my beloved Tele 6922's.
I've lstened to a lot of Amperex/Phillips, Siemens, Japanese and Russian 6DJ8/6N23/6922/7308 over the decades and in different preamps. They all had their charms, but the Teles ultimately won me over. The JJs sound so close to the Teles that I have trouble telling them apart. The JJs don't last as long as the Teles, but you can buy four or five pairs of the JJ tubes for what one pair of Teles might cost you.
As always, your mileage may vary.
Thanks very much for the suggestion, I bought a pair of the JJ's. Very nice tubes, pretty much what I was looking for, I am very happy with their sound. We'll see in extended listening, but very pleased so far.
Thanks again - Rick
Okay, that's interesting.
As I've typed on threads before, my ears may not be good enough for this hobby.
But they are good enough to let me know I like tubes.
I wish you success in the quest.
Don't know if this has been mentioned, but the 6CG7/6FQ7 is a nine-pin electrical equivalent of the 6SN7.
I have in the past used a 6CG7/6FQ7 as a drop-in, pin compatible replacement for a 6922. This was in an Counterpoint SA3000. There we no ill-effects from using it in that application. On the other hand, I ultimately felt it sounded inferior to virtually all the other true 6DJ8 variants I experimented with. Not that the 6CG7/6FQ7 sounded bad, just not as good as the tube the circuit was designed for.
the 6DJ8 is about 33 or so. The 6SL7 is a lot higher, and the 6SN7 is lower.
If you have a 47K plate load the 6SL7 is out of the question.
So only the 6SN7 would work and to do that, you'd have to changed out the cathode resistor that is likely setting the operating points of the two tubes in the circuit.
A schematic would be helpful.
You also cannot expect the gain on account of the lower mu. You'll need a sine wave generator and an oscilloscope at the least in order to make this change- plus a good soldering skill. I would be hesitant to attempt this without a schematic.
There was a recent thread on UK site HiFi Wigwam where a guy put a lot of money into boutique 6SN7s plus adapters and 6N30 tubes for a piece of equipment designed for 6N6P tubes. He hadn't even tried the 6N6P tubes that came with it. He'd just read somewhere that 6SN7 tubes were "better" so should sound better in his equipment. Of course they didn't. In the end he put the 6N6P tubes in and surprise, surprise, they sounded the best.
It may well be the case that you can "design" a better sound. But do it the right way - teach yourself tube technology and then design the circuit correctly. If you don't understand the circuit how can you modify it? Plenty of tube tutorials and books available. Something to do over the winter if you love tubes.
Oh well, I guess I didn't expect a summary dismissal.
Anyway, please read no emotion, sarcasm, or ingratitude into my response.
The circuit in question is an srpp, driving a 47k load. My understanding is that the load is an integral part of the srpp circuit.
I own, and have tried, quite a few NOS 6DJ8/6922, the Holland Amperex are nice, but I like the genuine '75 Reflektor 6N23p a bit more, (I suspect it has a bit of 2nd harmonic as strings are somewhat on the "sweet" side). So, it's not for lack of trying on my part.
The 6SL7 idea was an inexpensive experiment (at first). It would have been really inexpensive if 6SN7's would have worked, I have a box full of all manner of those. So, $24 for a pair of adapters, $50 for a good pair of Sylvanias 6SL7's.
The Sylvanias sounded very good, but.....
Tung Sol BGRP's, brown base, (6SU7GTY's actually) are not obscenely priced. So, why not? And, as it turns out, sound fantastic in this circuit, as is. Top to bottom, "sounstage", decay, layering, simply beyond what I would have imagined. And, by way of just an oddity/comment, they run extremely cool to the touch. 132 degrees after 2 hours listening (says the IR gun).
Yes, I will learn more about circuit design. I just thought I'd ask a question.
Thanks - Rick
Hi again. What I was doing was encouraging you to learn a bit about tube circuits so you could avoid adapters. This is useful in many ways - less expense, less clunky, better contacts in a proper socket.
For instance it's not difficult to substitute a loctal socket for an octal one. This allows you to use cheaper tubes in many instances. The holes in the chassis should be roughly the same. Not so easy if you want to use an octal tube in a 9 pin socket, though.
So I guess you could start with adapters. But if you have the time and motivation, move closer to understanding how a circuit works. Quite a long-term project since you need to be safe with high voltages, but many of us have embarked on self-education about tube circuits. It's not for everyone, but it's an option.
Thanks Andy, sorry I misinterpreted your post. Though I did take your suggestion. I've been reading a bit on TubeCAD.com. I do have "passable" soldering ability, as well as respect for "high voltage". Before retiring, I was a Generation Technician at a 100Mw "Peaker Plant". So I have at least a primer in electrical theory.
I appreciate the encouragement.
The 6SL7 exhibits very high plate resistance and very low transconductance.
The 6922 exhibits very low plate resistance and very high transconductance.
The 2 types are NOT compatible.
Definitely leave well enough alone and find a 6DJ8 family variant you can "live" with. Among current production variants, the tube New Sensor sells under the Genelex Gold Lion label has a reputation for being "warm" sounding.
Ok, so if someone can check my "understanding" on this.
After reading, and studying the srpp circuit, it is in fact, only simple on the surface. It is, in reality, an interwoven balancing act, where one modification in component "value" affects all other "values". It also must be designed around a specific load, as the load is in fact part of the circuit, and thereby a component "value" in itself.
The 6SL7 doesn't really lend itself to this particular application due to it's high amplification factor/mu. As a drop in, it can sound nice with a signal of low voltage swings. But add in a more dynamic signal, and those voltage swings can become extreme, and not particularly "linear" in actual application. The 12xx7's would also fall into this category?
While the 6SL7, could be designed to work, other tubes are more suitable for an output stage, (probably why it's not often seen in this application?). But by it's nature, the srpp can also give substantially variable results, due to it's load sensitivity.
Would this be at least partially correct?
But that fact never stopped anyone from trying... and often liking the result. :)
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