ECC82/12AU7 Line Preamp - Page 3 - diyAudio
Go Back   Home > Forums > Member Areas > The Lounge

The Lounge A place to talk about almost anything but politics and religion.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 16th March 2012, 01:57 PM   #21
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
No, not my reference source but his. In a discussion about 'electron clouds' in valves he refers me to a poor Wikipedia entry on electron clouds in accelerators. I was merely pointing out that this is irrelevant.

Where did I say that distortion is not related to linearity?

He keeps wanting to reduce space charge, because he seems to think it creates. nonlinearity. I keep pointing out that space charge is a necessary part of normal valve operation. Linearity in normal triode operation is created by the grid and anode having the same 3/2 power law, due to geometry. Getting rid of space charge increases noise (that is how noise diodes work) and damages the cathode: it is known as temperature-limited operation. Is that sound design practice?
  Reply With Quote
Old 16th March 2012, 02:32 PM   #22
diyAudio Member
 
Join Date: May 2007
What´s so good about this SRPP? It might look promising at the 475mV input you show but low gain of 12dB and mediocre distortionfigures at higher levels is not what I would use driving a 845. An unlinear 12AU7 is still an unlinear 12AU7 even when driven close to breakdown Ua.
  Reply With Quote
Old 16th March 2012, 02:50 PM   #23
Cassiel is offline Cassiel  Libya
diyAudio Member
 
Cassiel's Avatar
 
Join Date: Sep 2004
Location: Madrid
Quote:
Originally Posted by Salas View Post
650!
I wouldn't spend 650 on a 12AU7.
__________________
Do your best and don't worry.
  Reply With Quote
Old 16th March 2012, 03:06 PM   #24
popilin is offline popilin  Argentina
diyAudio Member
 
popilin's Avatar
 
Join Date: Oct 2010
Location: Traslasierra
Hi jmillerdoc
Thank you for coming to my rescue !!!
I agree with you and that was the point all the time: distortion is due to nonlinearity in valves, and yes electron cloud effect in a valve is called space charge, that affects linearity.
I'm sorry if I insist with Planck constant experiment, it was made with a vacuum photodiode and reveals that space charge increase significantly valve nonlinearity, even at Quantum levels. I'm sorry, but the paper file is corrupted and big to upload.
I'm sorry for the Wiki, as I said my reference are Landau-Lifshitz, Cohen and why not Jackson's Classical Electrodynamics, but I haven't a scanner, neither the time.
I'm not an Electronics Engineer, I don't know the right search, BTW for the level of discussion Wiki is enough.
I made a thought experiment with an underrated valve, and the explanation from my little brain was the electron cloud effect.
Best regards
Johann
  Reply With Quote
Old 16th March 2012, 03:17 PM   #25
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
I have a copy of Landau and Lifshitz (the classical theory of fields). Could you direct me to the point in the book where they say that the presence of a cathode space charge in a valve causes nonlinearity? Or Jackson.
  Reply With Quote
Old 16th March 2012, 06:25 PM   #26
diyAudio Member
 
Join Date: Dec 2008
Location: North San Diego, CA
Default 12au7 as Mu follewer or srpp

I did extensive tests on using the 12au7, 6bk7, and 6sn7 tube in this mode

I built a tube mike preamp, using two 12au7s as line out trans stage.

Running three triodes on bottom, and one on top gave me the most output at the lowest impedance

Same with other tubes, running two or three triodes in parallel on bottom and one on top gave much more power.

The surprise tube was a 6gu7, a lot more low impedance drive than a 6sn7!

I have to find my notes, then I can publish

So if you use on 12au7 in parallel on bottom, and one triode on top, then you have a third triode for the bottom.
  Reply With Quote
Old 16th March 2012, 06:32 PM   #27
diyAudio Member
 
jmillerdoc's Avatar
 
Join Date: Mar 2009
Location: Lawton, OK, USA
I don't think he means to say literally get rid of the space charge (electron cloud) but to overcome it's adverse effects. It does have adverse effects as well as good effects (clearly without a cloud of electrons created by the thermionic effect there would be no electron tube to speak of) Unfortunately, in triodes at higher frequencies, the capacitance between the anode and grid electrodes can cause positive feedback, regeneration, or oscillation, or other reactances with the circuit. As i rcall, adding various grid in part works by reducing the inter tube capacitances which effect a whole host of things.

All i am saying is with the possiblity of language barriers here internationally we should be careful not to jump to conclusions and try to read between the lines when we can.

As far as linearity it is inferred....
  Reply With Quote
Old 16th March 2012, 07:20 PM   #28
popilin is offline popilin  Argentina
diyAudio Member
 
popilin's Avatar
 
Join Date: Oct 2010
Location: Traslasierra
Hi DF96
Neither Landau, neither Lifshitz, neither Jackson wrote anithing about valves, only basic Physics that lets us understand the Laws of the Universe.
If you wish to read

Electrodinámica Clásica-John David Jackson-Editorial Alhambra-Segunda edición 1980-Capítulo 15-Página 713-Radiación de frenado
15.1. Radiación emitida durante las colisiones
I'm sorry it's in Spanish, but I think the John Wiley & Sons edition can be consistent.

Théorie des Champs-Landau et Lifshitz-Physique Théorique-Tome II-Éditions MIR 1970-Chapitre IX-Page 242-Rayonnement de Freinage
70. Rayonnement lors d'interaction coulombiene
I'm sorry it's in French, but I hope is consistent with your copy.

Lectures are about colitions between charged particles.
Like electrons (good boys) with electrons of the cloud (bad boys)

Any good book about Quantum Mechanics can illustrates Planck constant measure experiment.
But I will tell a simplified story, and I hope you understand my point.
Einstein eq. for photoelectric effect
E = h f
Gives us measure h as the slope of the straight-line E(f), I used a vacuum photodiode, a monochromator as light source, a Voltmeter and a pico-ammeter,
with the pA-meter good I obtained
h = (6.62 +/- 0.07) x 10^-34 J s
When the most sensitive scale of pA-meter was broken (Keithley) I must use a less sensitive scale, with more photons, and
h = (2.55 +/- 0.55) x 10^-34 J s
The reason? more photons => more electrons => more electrons in the cloud=>electrons arived at anode with less energy due to collisions.
Curiously the straight-line became more and more in a curve like a valve curve, (of corurse I used a vacuum photodiode)
The conclusion was the electron cloud afected severely the valve linearity.

Last edited by popilin; 16th March 2012 at 07:23 PM.
  Reply With Quote
Old 16th March 2012, 07:52 PM   #29
popilin is offline popilin  Argentina
diyAudio Member
 
popilin's Avatar
 
Join Date: Oct 2010
Location: Traslasierra
Hi ElectricMan
Please, publish your results

Hi jmillerdoc
Yes, without the electron cloud we haven't a valve anymore, I'm not so fanatic.
Your diagnostics looks good to me, I don't know about the capacitance and feedback part, but I agree with you in almost everything.
There are people who undestand that they want understand.
Believe me, the electron cloud/space charge can be good, but for me was a total PITA.
Day by day broken my mind....until my discovery
  Reply With Quote
Old 16th March 2012, 07:52 PM   #30
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
So your personal opinion that space charge reduces valve linearity in a thermionic triode is based on a photoelectric diode experiment to measure Planck's constant? The former is based on voltage change; the latter on light frequency and intensity. Have you ever wondered why the standard valve textbooks never mention this effect you have discovered?

Quote:
Originally Posted by jmillerdoc
Unfortunately, in triodes at higher frequencies, the capacitance between the anode and grid electrodes can cause positive feedback, regeneration, or oscillation, or other reactances with the circuit. As i rcall, adding various grid in part works by reducing the inter tube capacitances which effect a whole host of things.
What has this got to do with linearity at audio frequencies?

I am aware of the possibility of language problems, which is why I have given popilin the opportunity to explain his ideas so I can see where he gets his strange idea from. I suspect he is confusing emission (whether thermionic or photoelectric) with total current. In the photodiode all the electrons emitted end up at the anode. In a normal triode this is not the case. Far from being a problem, the space charge is a necessity. Not to be reduced, but encouraged.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
ECC802S 12AU7 ECC82 heater question korabetsni Tubes / Valves 8 3rd July 2012 01:03 PM
12au7 ecc82 nigelwright7557 Parts 0 29th March 2010 02:07 PM
FS: single nos telefunken ECC82 (12au7) PreSapian Swap Meet 0 4th January 2010 04:03 AM
Do I need a Trafo for the HV in my 12AU7 (ECC82)? DaMeat Tubes / Valves 13 10th August 2007 11:08 AM
line preamp using 6SN7 instead of 12AU7 JPS Tubes / Valves 11 23rd May 2007 01:05 PM


New To Site? Need Help?

All times are GMT. The time now is 09:31 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright ©1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2