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My input driver tubes 12ax7, 5751, 12at7 and 12au7 all seem to give the same volume ... any ideas?

post #1 of 32
8/3/11 at 2:37pm
Thread Starter 

Hello Head-Fi Mavens,

 

     I am running a Ming-Da MC-84C07 from a Grant Fidelity Dac-09 (Dac-09 tube out ... from USB PC) and it does not seem to matter a lot if I use 12ax7, 5751, 12at7, 12av7 and 12au7 as input drivers in the Ming-Da as they all seem to have approximately the same volume to my ears ... and the volume control stays essentially at the same place too ... I was anticipating a huge reduction in volume especially with the 12au7s ... which have 19% of the gain of an 12ax7 ...  this is kind of nice actually as there are many low priced NOS tubes to be had ... especially the 12av7s and 12au7s ...  but can anyone tell me why i don't hear a huge difference?

 

12ax7 = 100 gain

5751 =   70

12at7 =  60

12av7 = 41

12au7 = 19

 

    Thanks in advance!    L3000.gif


Edited by dancingpotato - 8/3/11 at 8:51pm
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post #2 of 32
8/3/11 at 6:45pm

Hi dancingpotato,

 

I also have same experience as you. trying so 12at7 and 12au7 to replace 12ax7 as it kinda a bit too much gain for headphone listening for me, only to be confused by the lack of change on the volume level.

 

I hope someone with more tube knowledge can answer this.

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post #3 of 32
8/3/11 at 7:25pm

Are  you are talking about the tube RCA outputs in which a change needs to be made on the circuit board in order for the volume control to control the RCA outputs? Otherwise I think that the tube is is just a buffer with no gain amplification.

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post #4 of 32
8/3/11 at 8:59pm
Thread Starter 

 Hello John,

   I am sorry I dont really understand your question ... but I am not referring to the RCA tube output of the GF Dac-09 when i talk about the tube rolling ... I am talking about the input drivers of the Ming-da. BTW my tube output of the GF Dac-09 is controlled by the volume knob of the GF.

 

The Ming-Da:

"The two EL84 tubes provide amplification and two 12AX7s are input drivers."  

http://www.pacificvalve.us/MDMC84C07.html

 

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post #5 of 32
8/3/11 at 9:01pm
Thread Starter 
Quote:
Originally Posted by IndieScent View Post

Hi dancingpotato,

 

I also have same experience as you. trying so 12at7 and 12au7 to replace 12ax7 as it kinda a bit too much gain for headphone listening for me, only to be confused by the lack of change on the volume level.

 

I hope someone with more tube knowledge can answer this.


Hi Indie,

 

   Kind of interesting isnt it? ... but it certainly opens up lots of possibilities to try other tubes ... and 12au7s are so cheap compared to 12ax7s.

BTW are u also using the Ming-Da or another headphone amp?

 


Edited by dancingpotato - 8/3/11 at 9:05pm
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post #6 of 32
8/3/11 at 9:16pm
http://www.audioasylum.com/scripts/d.pl?audio/faq/joes-tubes.html
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post #7 of 32
8/4/11 at 12:31am
Quote:
Originally Posted by john57 View Post

Are  you are talking about the tube RCA outputs in which a change needs to be made on the circuit board in order for the volume control to control the RCA outputs? Otherwise I think that the tube is is just a buffer with no gain amplification.



hi john,

 

I also not really sure what the meaning of your statement there. mingda mc84c07 dont have a RCA outputs on it.



Quote:
Originally Posted by dancingpotato View Post




Hi Indie,

 

   Kind of interesting isnt it? ... but it certainly opens up lots of possibilities to try other tubes ... and 12au7s are so cheap compared to 12ax7s.

BTW are u also using the Ming-Da or another headphone amp?

 



hi dancing,

 

yeah, I also using mingda mc84c07 (its also listed on my signature tongue_smile.gif). I also find 12at7 tend to be more cheaper than 12au7 somehow. also if my ears not decieving me 12au7 kinda too distorted for my ears.



Quote:
Originally Posted by Happy Camper View Post

http://www.audioasylum.com/scripts/d.pl?audio/faq/joes-tubes.html


hi happy,

 

not sure what you mean by that link. as far as i know tht link only shows joe's preference on some 12au7, 12ax7 and 6jd8.(have that link on my bookmark already)

 

 

I guess what I'm trying to say is something like this http://thetubestore.com/gainfactor.html , or maybe those only apply to guitar amp?

 

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post #8 of 32
8/4/11 at 8:16am
Thread Starter 

http://cydathria.com/fdm/12AX7_sub.html

 

Here is another page with tube substitution data which also refers to guitar amps ... so maybeeeeeeeee ?

 

BTW IndieScent ... all the tubes sound great in MY Ming-Da ... no distortion at all with the 12au7s

... maybe because I am running it from the Dac-09 or maybe because I am going deaf?

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post #9 of 32
8/4/11 at 9:01am
Quote:
Originally Posted by dancingpotato View Post

http://cydathria.com/fdm/12AX7_sub.html

 

Here is another page with tube substitution data which also refers to guitar amps ... so maybeeeeeeeee ?

 

BTW IndieScent ... all the tubes sound great in MY Ming-Da ... no distortion at all with the 12au7s

... maybe because I am running it from the Dac-09 or maybe because I am going deaf?

 

it could also be my 12au7 that not good. or maybe distorted is the wrong way to describe it, it's more like I like 12at7 and 12ax7 betterL3000.gif

like many head-fier say here, YMMV
 

 

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post #10 of 32
8/4/11 at 3:31pm
Thread Starter 

 Indie ...   I took out the driver tubes to see if the Ming-Da would work without them ... thank goodness it did not ... so they are just not

cosmetic glowing ornaments ... phewwwwwwww  beerchug.gif

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post #11 of 32
8/4/11 at 3:51pm

I had always thought that a 12AU7 could not be substituted for a 12AX7.  Guess that is not always the case.

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post #12 of 32
8/4/11 at 3:58pm
Quote:
Originally Posted by BmWr75 View Post

I had always thought that a 12AU7 could not be substituted for a 12AX7.  Guess that is not always the case.


Pinout is the same, which I figure you know, and one is a current tube the other, the 12AX7 is a voltage tube. So normally in a design they have specific purposes and would not seem to be interchangeable. Some circuits allow for it though and if it is the input tube, it is odd that a volume change is not noticed. 

 

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post #13 of 32
8/4/11 at 4:41pm
Quote:
Originally Posted by dancingpotato View Post

 Indie ...   I took out the driver tubes to see if the Ming-Da would work without them ... thank goodness it did not ... so they are just not

cosmetic glowing ornaments ... phewwwwwwww  beerchug.gif



blink.giferr is that a safe thing to do?



Quote:
Originally Posted by BmWr75 View Post

I had always thought that a 12AU7 could not be substituted for a 12AX7.  Guess that is not always the case.

 

Quote:
Originally Posted by jamato8 View Post




Pinout is the same, which I figure you know, and one is a current tube the other, the 12AX7 is a voltage tube. So normally in a design they have specific purposes and would not seem to be interchangeable. Some circuits allow for it though and if it is the input tube, it is odd that a volume change is not noticed. 

 


I asked sometime ago directly to MeiXing and here the response:

 

Quote:

Dear Sir,

Thanks for your email.

You can use 12AT7 or 12AU7 as the substitution for 12AX7 but the sensitivity for MC84-C07 will be lower and you must use strong signal input to get the sound effect. We haven't heard about 5751.

If you have any questions, please feel free to contact us.

Best regards,

 

so, jamato. the difference should be kinda substantial between 12ax7 and 12au7 right?(in regard volume level)

 

@BmWr75: any hum with lcd-2 using mc84?

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post #14 of 32
8/4/11 at 4:51pm
Thread Starter 
Quote:
Originally Posted by dancingpotato View Post

 Indie ...   I took out the driver tubes to see if the Ming-Da would work without them ... thank goodness it did not ... so they are just not

cosmetic glowing ornaments ... phewwwwwwww  beerchug.gif



blink.giferr is that a safe thing to do?

=====================================================

   Well to make sure it was safe I put my finger in a lamp socket while holding the Ming-Da between my legs  ... it gave me a wicked tickle but no permanent damage was done to either the me or the amp. However i now talk like a pre-teen going through hormone therapy... basshead.gif

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post #15 of 32
8/4/11 at 5:00pm

Don't have a schematic for this unit, but if there is no cathode bypass capacitor, the gain of the circuit

given enough tube gain would be (RL+Rp)/Rc. If the circuit gain is say 10, then the changes between

any of those input tubes would be very little.


Edited by kevin gilmore - 8/4/11 at 5:02pm
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