I'm sorry if this thread is useless, I'm just trying to know what the difference are between those tubes, I know that 12AU7 are non linear and distorts quickly but most of the distortion are 2nd order making it more musical, and that the 12A_7 series uses 12v where 6DJ8 and 6AK5 uses 6.3v.
To answer some of the questions here about the amp that uses 12AU7 and 6DJ8, I found a headphone amp (little bear p10) that can use both 12AU7 and 6DJ8 with a switch.
I am new to this DIY tube stuff, I just want some sort of generalisation toward the tubes that I am asking above. I know it all comes down to the circuit design, but I also think that each tube has their own sound. Some may prefer KT66 than El34, some may prefer EL34 than KT88. I'm sorry if I'm wrong, I just want to learn more about the magic of the tube world
To answer some of the questions here about the amp that uses 12AU7 and 6DJ8, I found a headphone amp (little bear p10) that can use both 12AU7 and 6DJ8 with a switch.
I am new to this DIY tube stuff, I just want some sort of generalisation toward the tubes that I am asking above. I know it all comes down to the circuit design, but I also think that each tube has their own sound. Some may prefer KT66 than El34, some may prefer EL34 than KT88. I'm sorry if I'm wrong, I just want to learn more about the magic of the tube world
It's called "tube rolling" and a lot of folks can be obsessive about it.
This is the difference between hollow state and solid state. Transistors are high gain, and that means that the performance is independent of the individual device selected, and more dependent on the external circuit constants. So long as the transistor can process the frequencies of interest, it doesn't make much difference which one you use, unless you need some special feature like an unusually low noise figure.
Tubes are low gain devices which makes the performance more dependent on the active device characteristics. It's one reason to use NFB: to even out performance. If you don't use NFB, then different tubes can lead to different sound.
And that's what it comes down to: personal preference. I favor 6L6-oids and TV deflection types even though these aren't seen as audio types and the spec sheets don't include any audio examples. For small signal types I've used: 6SN7, 6SL7, 6BQ6, 6FQ7.
The 12AU7 Transconductance Gm, Plate Resistance rp, and u (mu), is completely different versus the Gm, rp, and u of a 6DJ8.
How they sound is partly due to how well you set the tube voltages, and tube current, in order to use each tube type at its optimal range of values.
Just changing the filament wiring, and nothing else in the circuit around the tube can not possibly make both the 12AU7 and the 6DJ8 sound at their best.
But, you will get a different sound, especially if there is no negative feedback that includes that stage in the feedback loop.
I hope that helps to understand, it is not as simple as changing filament wiring.
How they sound is partly due to how well you set the tube voltages, and tube current, in order to use each tube type at its optimal range of values.
Just changing the filament wiring, and nothing else in the circuit around the tube can not possibly make both the 12AU7 and the 6DJ8 sound at their best.
But, you will get a different sound, especially if there is no negative feedback that includes that stage in the feedback loop.
I hope that helps to understand, it is not as simple as changing filament wiring.
Last edited:
Sorry for changing the topic of this thread a bit. I bit the bullet and went for a 12AU7 based amp, as I heard that it produces 2nd harmonic distortion making it more tubey. I attached the schematic that I based my amp of, does changing the tubes matter (is tube rolling worth it?) toward the sound? What is the purpose of the tube, is it a solid state with a tube ornament or is it a true hybrid? Thanks!
Attachments
That's about as basic as you can get for a class-A tube hybrid and, yes, all of your voltage gain comes from the 12AU7.
That 12V B+ is going to be the source of most of your distortion and kind of does that tube a disservice. I doubt most people could hear the linearity difference between a 12AU7 and a 6DJ8.
If you put large enough heat-sink and watch your solid state class-a current(adjustable by swapping out R4) you can crank that to 24 or 36V for better sound. Though that does add a challenge of the heater power.
Could also look for a 12U7 or a pair of 12AE6 or 12FK7.
That 12V B+ is going to be the source of most of your distortion and kind of does that tube a disservice. I doubt most people could hear the linearity difference between a 12AU7 and a 6DJ8.
If you put large enough heat-sink and watch your solid state class-a current(adjustable by swapping out R4) you can crank that to 24 or 36V for better sound. Though that does add a challenge of the heater power.
Could also look for a 12U7 or a pair of 12AE6 or 12FK7.
Take a look at the family of plate curves for the 12AU7 and the 6DJ8.
A 12AU7 with 10V plate to cathode, and 0V grid to cathode, has about 1mA of plate current.
A 6DJ8 with 10V plate to cathode, and 0V grid to cathode, has about 2mA of plate current.
With such a low plate voltage, and the grid at 0V, there will be grid current due to the contact potential . . . even before you apply signal to the grid.
With only a 12V B+, you are starving the 12AU7 and the 6DJ8 tubes.
That is fine for a Guitar Effects Box.
Terrible for Hi Fi.
The sound you will get depends on the input signal amplitude, signal source output impedance, and the particular 12AU7 tube you use, or the particular 6DJ8 tube you use.
At that low of a B+, different manufactures of a given tube type, may perform completely different there.
The above are just my opinions, try it for yourself.
"You should make things as simple as possible, but no simpler" - Albert Einstein.
His birthday was last Sunday, March 14 (3.14). That was International Pie day (International pi day).
We had a co-worker who correctly repeated from memory, the first 150 numbers of pi.
Pie ends. The numbers of pi never ends.
A 12AU7 with 10V plate to cathode, and 0V grid to cathode, has about 1mA of plate current.
A 6DJ8 with 10V plate to cathode, and 0V grid to cathode, has about 2mA of plate current.
With such a low plate voltage, and the grid at 0V, there will be grid current due to the contact potential . . . even before you apply signal to the grid.
With only a 12V B+, you are starving the 12AU7 and the 6DJ8 tubes.
That is fine for a Guitar Effects Box.
Terrible for Hi Fi.
The sound you will get depends on the input signal amplitude, signal source output impedance, and the particular 12AU7 tube you use, or the particular 6DJ8 tube you use.
At that low of a B+, different manufactures of a given tube type, may perform completely different there.
The above are just my opinions, try it for yourself.
"You should make things as simple as possible, but no simpler" - Albert Einstein.
His birthday was last Sunday, March 14 (3.14). That was International Pie day (International pi day).
We had a co-worker who correctly repeated from memory, the first 150 numbers of pi.
Pie ends. The numbers of pi never ends.
Last edited:
Some people make that their new hobby...
Like a dog chasing it's tail...
To make sure no tube rolling is required in the amps i build, i use television tubes. No hype (yet) about those....
I sometimes need to repair microphones, these require very low noise tubes, so here i will roll some tubes but not by brand. I found however that the russian tubes are very good in this respect, better then most "hyped" Siemens or Telefunken gold pins etc.
So it is up to you to change hobby or not.
Best regards. Frank
Like a dog chasing it's tail...
To make sure no tube rolling is required in the amps i build, i use television tubes. No hype (yet) about those....
I sometimes need to repair microphones, these require very low noise tubes, so here i will roll some tubes but not by brand. I found however that the russian tubes are very good in this respect, better then most "hyped" Siemens or Telefunken gold pins etc.
So it is up to you to change hobby or not.
Best regards. Frank
incredible80,
That is a great question!
Take this set of measurements as a single example . . .
Can you hear the difference of harmonic distortion of good well working set of 6SN7 tubes:
2nd Harmonic -31.8 to -39.5 dBc, a difference of 7.7 dB
3rd Harmonic -54.5 to -78.7 dBc, a difference of 24.2 dB
In an amplifier with no negative feedback (no local and no global negative feedback),
Some people may be able to hear the difference.
Then, include a bunch of local negative feedback or a bunch of global negative feedback; or a moderate amount of each local and global negative feedback . . .
And then anybody that can hear the difference, is not doing a properly administrated AB double blindfold test.
The above are just my opinions.
That is a great question!
Take this set of measurements as a single example . . .
Can you hear the difference of harmonic distortion of good well working set of 6SN7 tubes:
2nd Harmonic -31.8 to -39.5 dBc, a difference of 7.7 dB
3rd Harmonic -54.5 to -78.7 dBc, a difference of 24.2 dB
In an amplifier with no negative feedback (no local and no global negative feedback),
Some people may be able to hear the difference.
Then, include a bunch of local negative feedback or a bunch of global negative feedback; or a moderate amount of each local and global negative feedback . . .
And then anybody that can hear the difference, is not doing a properly administrated AB double blindfold test.
The above are just my opinions.
Last edited:
I apologize if my earlier response sounded harsh.
But the point I was trying to make is that the "sound" of a particular tube will vary considerably based on how it is used in a circuit and on what operating points (voltage and current) are used. So simply asking what a particular tube "sounds like" is pretty much a meaningless question.
If you post a link to the amp in question and include a schematic you're likely to get more information that's useful.
As for tube specs, I posted a link to a site with tube datasheets. Here it is again. If there's a particular tube you're interested in, just look it up.
Frank's electron Tube Data sheets
The 12DQ6 doesn't have power output listed because it was not originally used as an audio output tube. That doesn't mean it can't be used for audio, but very few people are likely to have experience using it so you may not get answers that are particularly definitive.
The EL84/6BQ5 is a popular audio tube used in both SE and PP designs. It's hard to make them sound bad. While I've never built anything with them, I have many vintage amps that use them and they always sound great to my ears.
Where you are located? If you're in the US, you might want to start with an EL84 amp pulled from an old console stereo and rebuild / modify it. That's a great way to get into tubes and is very inexpensive.
As others have said, 81db speakers are extremely inefficient. I don't recall ever even hearing about speakers that are rated that low, which also makes me question their quality. I'd suggest that you look for speakers with a more normal level of efficiency unless you listen at extremely low volume.
I have a pair of 4 inch that are 83db but useable to 40Hz. I have a pair of 5 inch that are 89db but only useable to 60Hz or so.
Sensitivity, Small box, LF response... Pick two
FWIW, I would run 6DQ6 in push pull with about 60mA idle using a B+ of about 320V, strapped as triodes using 200R-270R screen resistor, loading 2k5-3k or so. Now that I realise that the 6BQ6 and the 6DQ6 have the same pinout, I can try a pair next time I have my amp configured for that socket/layout. I only have two, so I'll have to do a left/right comparison.
Sensitivity, Small box, LF response... Pick two
FWIW, I would run 6DQ6 in push pull with about 60mA idle using a B+ of about 320V, strapped as triodes using 200R-270R screen resistor, loading 2k5-3k or so. Now that I realise that the 6BQ6 and the 6DQ6 have the same pinout, I can try a pair next time I have my amp configured for that socket/layout. I only have two, so I'll have to do a left/right comparison.
Last edited:
Le Renard
In my experience, the 6/12/25-BQ6 sounds great. The A Number One problem with the 6BQ6, and the reason why the spec sheet makes no mention of any audio applications is that you can't use 'em as SE finals. The plate characteristics (attached) show that the most linear part of the characteristics are well within red plate territory. Of course, you could drop the screen voltage, but you lose lotsawatts by doing so. The 6BQ6 is best run as a PP, Class AB1 final to stay in the most linear regions. That's also true of other TV HD finals.
As for sonic performance, the 6BQ6 is like the famous 6V6, only capable of much more output. If you do some spec busting, and increase the IPQ to 50mA (PD= 17.5W v. 11W rated) you can reduce the THD and improve the sonic performance. Being that these TV HD types were designed to run at full RMS continuously, the rating is very conservative. Since audio is far from "brick on the key" operation, you can get away with spec busting without compromising life.
The Twin-T test shows mainly h3 with a trace of higher order harmonics, so you don't get that pentode nastiness at least until you're close to clipping. All you need is just enough gNFB to take the edge off. The 'DQ6 probably operates similarly.
Attachments
Last edited:
incredible80,
How does an output tube sound?
A great question, for which there is no single answer.
What is the circuit?
You mentioned single ended.
Triode Wired mode?
Ultra Linear mode?
Beam Power / Pentode mode?
Will there be any negative feedback?
No negative feedback?
Global negative feedback?
Local negative feedback? which type(s)?
Combination of the above negative feedbacks? (multiple loops)
B+ voltage, plate current, plate load impedance?
Driver distortion, how much versus the output tube? (possible cancellation of the 2nd H).
Loudspeaker impedance versus frequency?
Etc.
And the same questions exist for a push pull amplifier.
People can comment for the sound of a particular output tube type in their amplifier, or in an amplifier they heard somewhere.
But what was the rest of the system: signal source, preamp, loudspeaker, room, room treatment, etc.?
Theoretical output power?
A set of plate curves can not give you that, unless you consider the loss in the output transformer.
Start with 12 Watts from the tube, and send that through an output transformer that has an insertion loss of 0.8dB.
Now that 12 Watts from the tubes becomes 10 watts at the amplifiers output terminals.
How does an output tube sound?
A great question, for which there is no single answer.
What is the circuit?
You mentioned single ended.
Triode Wired mode?
Ultra Linear mode?
Beam Power / Pentode mode?
Will there be any negative feedback?
No negative feedback?
Global negative feedback?
Local negative feedback? which type(s)?
Combination of the above negative feedbacks? (multiple loops)
B+ voltage, plate current, plate load impedance?
Driver distortion, how much versus the output tube? (possible cancellation of the 2nd H).
Loudspeaker impedance versus frequency?
Etc.
And the same questions exist for a push pull amplifier.
People can comment for the sound of a particular output tube type in their amplifier, or in an amplifier they heard somewhere.
But what was the rest of the system: signal source, preamp, loudspeaker, room, room treatment, etc.?
Theoretical output power?
A set of plate curves can not give you that, unless you consider the loss in the output transformer.
Start with 12 Watts from the tube, and send that through an output transformer that has an insertion loss of 0.8dB.
Now that 12 Watts from the tubes becomes 10 watts at the amplifiers output terminals.
Last edited:
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.