|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
71.0.213.197
In Reply to: RE: 6SF5 to 45 design help posted by Triode_Kingdom on August 24, 2014 at 13:46:11
You can roll all the high mu octals you can dream of as the driver, and the 12AX7, properly implemented, will eat them ALL and can not be beat. The problem you have is, you have not figured out WHY this is so, but I sure have !!!
I'll award a STAR to the first person who can post why this would be so, lets see if anyone can get it !!!
Jeff Medwin
Follow Ups:
Would you still use the 12AX7 as a phono amp tube?
Only thing I can see as an advantage of the miniature tube would be structural stiffness due to the size of envelope and consequently the internal parts would be smaller. Of course, the larger size of the octals has long been given as the reason for their superior sonics.
I have four of those TECH TUBE 12AX7s - the one's that look nothing like any 12AX7 you have ever seen. Would your reasons apply to those, also?
SO how long do we have to wait before you tell your reasons?
Take care,
The octal socket requires a solder joint, and a different metal type ( pin ) to attach each element in the tube. So, a 6SL7 will have 8 extra solder joints, and dis-similar metals, whereas a dual triode 9 Pin miniature will have NONE of those extra parts.
Rick, it won't make much difference on a low or medium mu tube, but on a high mu tube, the 12AX7 having a mu of 100, used as the first stage in a two stage DC amp, it is audible on a good execution. The ultimate in clarity and pristine playback, only comes with a non-octal miniature there.
Feel free to use 12AX7s in phono stages. Excellent.
I don't quite know what Triode-Kingdom is talking about, when he claims the 12AX7 tube is non linear. I think its hard to beat a good 12AX7 in certain positions, recall using Telefunken smooth plates, etc etc ?? Of course, being sensitive, high mu, it takes a better than usual execution of the power supply, which most designers and DIYers ignore or "miss", to get the most from them.
Regards,
Jeff Medwin
12AX7 as phono amp. I have no issue, but use only a Brimar CV4004 or a lower cost USA manufactured Westinghouse 12AX7 short narrow plate.
12AX7 was a no go for a tube SUT replacement I built. I used an Amperex 6922.
Yo,
I looked up your system on line. Very nice, I LIKE what you did with your speaker execution of Fortes. Impressive to me. Bet its really good.
Over time, I will head in your direction with a two-way ALTEC A7-800 system I am working on now. Stay in touch.
Jeff Medwin
I suspect drlowmu is referring to gold-plated pins. Regardless, miniatures like the 12AXAs simply aren't as linear as their predecessors. They became popular in an era when it didn't seem to matter; the '50s and '60s were saturated with pentode-output amps that of necessity applied heavy doses of negative feedback. However, we've learned a thing or two since then, and we now realize that if you're building an amp or preamp all with triodes, the inherent linearity of every device matters a great deal.
--------------------------
Buy Chinese. Bury freedom.
Is it because you can parallel both sections of the 12AX7 dual triode? (The 6SF5 is a single triode)
Al F.
No, as soon as you parallel two high mu triodes you get a skewed effect which will be clearly audiible in these types of two stage amps. With a mu of 100 tube, everything is hyper critical to get it optimized, which few ever do !!
Parallel the 12AX7 input/driver stage and enunciation and diction will suffer, you won't be able to make out all the words sung in any prisine manner. Thats one of the things wrong with the Shishido L-W.
The 12AX7 is so critical in this spot, that if you parallel the dual triode RECTIFIER tubes, and use two 5U4Gs, it will skew the diction in the audio stages on voice. The "straight" E.E. types ( narrowly educated ) can't figure that one out it seems. Well, its clearly audible to any good listener!! I am thinking of diction and enunciation in terms say, of my fun to hear, wonderfully recorded D'Oyly Carte Gilbert and Sullivan original issue London L.P.s
Jeff Medwin
!
The Mind has No Firewall~ U.S. Army War College.
"lets see if anyone can get it"
A.) The pins are shorter.
B.) Miniature sockets exhibit lower DCR.
C.) Reduced micro-resonance in the smaller structure.
D.) Manufacturing techniques improved in the '50s.
E.) Just because. (my 10-year-old contributed this one)
How'd I do?
--------------------------
Buy Chinese. Bury freedom.
You are getting somewheres, go back and ask your ten year old to LOOK at the construction of a 6SL7 and a 12AX7, think about it, maybe the second try will be Golden for the kid.
HINT : What is simpler about the 9 Pin miniature ???? Less is more.
Jeff Medwin
!
The Mind has No Firewall~ U.S. Army War College.
In my GE "Essential Characteristics" book it reads :5751 ( Special 12AX7 )
and has a mu of 70 instead of 100.
A 5751 will out-perform an octal 6SL7 as a input/driver tube in a really good L-W, but no one yet has offered a reason as to why this is so, my little challenge.
I'd much prefer to use a regular 12AX7, and avoid a 5751, because of the 12AX7's superb tube rolling possibilites and general availability.
Cheers...
Jeff Medwin
Edits: 08/24/14
Can you please define what you mean when you say one tube can "beat" or "outperform" another? That terminology has absolutely no meaning.
--------------------------
Buy Chinese. Bury freedom.
It means diction and enunciation will be audibly better with one tube over the other, you can make out all the words clearly, versus a lack of TOTAL diction or enunciation. Nothing skewed, garbled, etc. We are all most familair with voice as a instrument of sound.
Its called listening I suppose.
Just have your ten year old look at both tube types, one in each hand, and you will see the difference easily. Your kid's first response was pretty good, but not definitive, correct.
Jeff Medwin
None of my amps are skewed or garbled. I've only ever heard that effect with miniature dual triodes.
--------------------------
Buy Chinese. Bury freedom.
The 12AX7 is prized because it id very easy to turn into a distortion machine; high gain and pass almost no current. Great where you need massive amounts of gain, like in phono or in amping guitar pickups. They hate driving loads, however.
12ax7s have high plate resistance so a grounded cathode circuit built with a 12ax7 will have higher output impedance than a grounded cathode circuit built with a tube that has lower plate resistance (assuming both circuits are built to achieve the same percentage of "mu" of the tube in use).
12ax7s have a low max plate dissipation rating so a circuit built with a 12ax7 cannot deliver as much current to the load as a circuit built with a tube that has a higher max plate dissipation rating (assuming both circuits are built to idle at the same percentage of max dissipation at idle of the tube in use).
High output impedance and low current delivery means circuits built with 12ax7s can only drive high impedance, non reactive loads.
This does not describe the load represented by a DHT grid.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Post a Followup:
FAQ |
Post a Message! |
Forgot Password? |
|
||||||||||||||
|
This post is made possible by the generous support of people like you and our sponsors: