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The Mind has No Firewall~ U.S. Army War College.
N/t
It's a 6SN7 in a noval package. A dual triode.
Can I use this in my pre amp,
I dug up an old thread on the AA forums and modified my Foreplay III to use the 6CG7's with a grounded shield and I was blown away! The bass bloomed and there is more depth to the sound (front-to-back soundstage). Female vocals almost have an eerie 3-D sound to them now as well.
For those considering this upgrade, I give it 3 thumbs up (???)! It only took about 30 minutes with a soldering iron:
1. Unhook heater wires from the 12AU7 tubes.
2. Unhook heater ground reference from Pin 9 of the one 12AU7.
3. Re-wire the heaters to Pins 4&5 of the 12AU7's (observe polarity!).
4. Tie the heater ground reference to Pin 4 of the one 12AU7.
5. Tie Pin 9 of both 12AU7's to the closest ground terminal (one used for cathode LED ground).
6. Replace 12AU7's with 6CG7/6FQ7's.
7. Enjoy!
The Mind has No Firewall~ U.S. Army War College.
If the heater supply is 6.3 volts and can deliver the increased current (.6 amps vs. .3 amps) it's a drop in replacement that is MUCH more linear.Edit, As JJ Triode pointed out, the above is only true after you rewire the heater connections on the tube socket.
Thanks again JJ for catching my mistake.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 07/12/15
The heater connection for 6.3V operation is different. In the 6CG7/6FQ7 there is 6.3V across pin 4 to pin 5 and no connection or ground on pin 9. For 12AU7 operating on 6.3V, pins 4 and 5 are connected together, with 6.3V between them and pin 9.
For 12V operation of the 12AU7 a 12FQ7 may be a drop-in.
.
Have Fun and Enjoy the Music
"Still Working the Problem"
My pre can use any type 12- type tube in this pre and any combination . But this tube I never heard of.
What preamp do you have?
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
It's A custom made Ton cat Audio pre, uses any combination 12a- tubes.
Without a schematic I can't really help or guide you.
Is it like this one?
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
It was design to take any 12au7 at or au and 5814a tubes, takes 4 tubes,
timīs stats are hard to believe!
in the 12AU7 gain position of my gear i checked nearly every estimated "better" replacement you can imagine like 6067, 5965, 12BH7, E80CC etc. but i always swapped back to 12AU7/ECC82 (Siemens E82CC long plates currently) as it always performed better than all the others!
N.
The times, they are changing...
You don't think that's true?
Some further points?
i)If you didn't change the circuit values for each of those potential substitute tubes they wouldn't be operating properly, anyway.
ii) Unless the tubes you are rolling are the same design, the circuit values around that tube position will almost certainly need to change. And that's only if there's sufficient reserve heater current
iii) The 12BH7 shouldn't need any circuit value changes but will draw more current, and if it can't the sound isn't likely to be any good. In a circuit that has enough current any 'to spec' 12BH7 will beat any such 12AU7.
Warmest
Tim Bailey
Skeptical Measurer & Audio Scrounger
For me it's the RFT. The RFT is ruthlessly revealing and many would say cold, or hard sounding. And to some extent that criticism is true, but what we so often find when rolling tubes it's all about synergies. Nowadays, the only piece if gear I have left that uses a 12AU7 is my Primaluna CD player. The sound of the RFT when paired with the (I know, I'm starting to sound like the spokesman for them) JJ 5751 is just beautiful. That same RFT with just about any other AX7 type I own always ends up being just too much and gets rolled out.
Unless a 12AU7 is used in follower mode (mu or cathode follower) with full degeneration ie 100% local feedback, they aren't a good audio tube at all. Not good for gain duty. Any working 12AT7 or AY& will eat them for breakfast.
This information has been around for a long time, and you haven't noticed?
If you want to improve the sound of a device with 12AU7s 'designed?' into them and used to provide signal gain, replace them with something else within the power transformer's heater limits.
If those limits won't allow you to do that, get rid of the device.
Rolling 12AU7s, in gain stages, is a waste of money and time.
Warmest
Tim Bailey
Skeptical Measurer & Audio Scrounger
I see you're quite definite re the 12AU7. I don't understand why so many amps are designed to use that tube, if they are so bad. Generally speaking the 12AT7 is easier to find in good shape and are less expensive than equivalent 12AU7s. I bought a little headphone amp, a Bravo 2 which uses `1 tube and it is a 12AU7. I found that rolling it had less of an impact on the sound than I usually find. I am not sure why this is but I suspect the SS element of the amp is it's output stage, which overwhelms the input stage signal. I like the amp, any way, but use my larger desktop with 6080s more than the Bravo. I haven't tried anything other than 12AU7s (ECC82s etc..) in it.
Steve
Because no 12AU7 made actually sounds good as a gain tube?Maybe?
And, likely you are you're own man, when it comes to audio. Good for you.
:-)
Warmest
Tim Bailey
Skeptical Measurer & Audio Scrounger
Edits: 07/10/15
I have a great deal of respect for our EE inspired and longstanding experienced inmates. My questions reflect.healthy and reasonable curiosity no offense intended.
now back to the discussion.
I don't know if the 12AU7 is a voltage amplifier in this little Bravo 2
headphone amp. They don't provide a schematic which I could send to you and evaluate. The structure is clear plexiglass but I don't know whether you can see into it. The power supply is a walwart.
I am still left to wonder why the 12AU7 is even in my Jadis Da-60, an expensive amp with big "iron". The DA-60 is an integrated amp, the pre amp section uses 3 X 12AU7s and 2 X 12AX7s. (all rolled to 5751s and 7316s.) A better example of this fundamental part can be found at garage1217.com "project Ember'. You would enjoy this one because of the variety of tubes you can use with it . Makes me think it's not doing anything of critical importance.
I guess that I will just take you and Eli's word for it. My favorite pre amp is a cheap 2 tube unit, using I bet another bad choice, 6SN7s. I know the 6G8F is a better choice I have already read about that here in the asylum. However my tube collection is full of these non linear tubes. Selling then and acquiring tubes to replace them is a daunting task.
Steve
I honestly don't know why firms like Jadis use 12AU7s, ever!Down here in Aussie we have an acronym BBB. Bullshit baffles brains.
A lot of what you can read here from audiophiles and in the 'high-end' press falls under that idea. Not all of it, mind.
Here's a thought to carry with you into life. 'It depends.'
Warmest
Tim Bailey
Skeptical Measurer & Audio Scrounger
Edits: 07/15/15
Well after that discussion re: the relative qualities of a 12AU7 and a 12AT7 I decided to try some of my 12AT7s. And would you believe it the 12AT7s with the first trial sound great! I am not sure if the increased mu is making them sound so much better or not. I have tried a number of 12AT7s, Brimar 6060s, Siemens ECC801S, Telefunken ECC82, and Mullard CV4024. They all sound really good, I just hope I am not destroying my little amp, (which cost less than some of the tubes I have used in it.) The amp is as I said a 1 tube hybrid headphone amp designed for a 12AU7. The only complaint is that I don't have much useable play on the volume knob, an almost otherwise inconsequential movement turns it way up.
Having a longer experience with tube electronics at this juncture, I am much more hesitant to just put in any tube with a pinout that will work. This time however it seems to be the right roll.
I am so pleased with this sound that I am going to start a thread about the 12AT7.
Steve
You nailed it. It does and always will depend.
Steve
"I don't understand why so many amps are designed to use that tube, if they are so bad."
In a word, money. The more linear Noval twin triodes, whose electrical characteristics are more or less the same, use twice as much heater current. Even if we postulate that tube costs are =, doubled heater current draw increases the cost of power "iron". Corporate "bean counting" is anything but a new phenomenon.
The 12AU7 is acceptable in the "concertina" phase splitter and voltage follower roles. In those jobs, the type's fundamental non-linearity is (more or less) a non-issue, due to local current NFB. Voltage amplification is a task the 'U7 triode is bad at.
Eli D.
The overall cost of producing the amp is heavily impacted by the transformers and other related bits of hardware used. The question then becomes why does it sound good and don't other tubes need roughly equivalent components? It seems penny-wise and pound foolish.
The audio-person hobby are intensely focused on the sound quality. It would seem easy to build a better sounding amp, using a different tube, that would sell well even if it were more expensive.
Steve
The 12AU7 tube is a good choice when you need limited gain and not a ton of drive. With a CCS plate load, their performance is quite good.
In a desktop hybrid amp, if you have a ~50V DC supply feeding the thing, then don't bother rolling tubes. If it has a proper power transformer, then go for it!
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