EF40 mc preamp - diyAudio
Go Back   Home > Forums > Source & Line > Analogue Source

Analogue Source Turntables, Tonearms, Cartridges, Phono Stages, Tuners, Tape Recorders, etc.

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 28th March 2011, 09:18 AM   #1
diyAudio Member
 
Join Date: May 2010
Default EF40 mc preamp

I have been looking for a tube phono stage to build to pair to my DL-103, and after being given a pair of EF40 tubes, I found these:Pentode configuration.jpg

Triode 33dB configuration.jpg

Triode 38dB configuration.jpg

First of all, I have no experience with RIAA stuff, so for those who do, do these networks check out?

Also, they all look to have high output impedance. Would adding a cathode follower be a good idea?

Last, seeing as the schematics are so similar, I was thinking about putting all three in the same chassis and using a 3 position switch to move between them.

Thanks in advance for any wisdom,
Alex
  Reply With Quote
Old 29th March 2011, 09:40 PM   #2
diyAudio Member
 
Join Date: May 2010
Any help would be really appreciated!
  Reply With Quote
Old 29th March 2011, 10:17 PM   #3
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 1
Not what you'll want to hear, but nonetheless true: a good RIAA stage is perhaps the most tricky and difficult bit to design and build. The circuits you linked are incomplete, made for a different tube, and far from optimum. This is not a likely path to success.

The EF40 has low microphonics but relatively high noise- is that really the tube you'd want to use?
__________________
And while they may not be as strong as apes, don't lock eyes with 'em, don't do it. Puts 'em on edge. They might go into berzerker mode; come at you like a whirling dervish, all fists and elbows.
  Reply With Quote
Old 29th March 2011, 10:37 PM   #4
diyAudio Member
 
Join Date: May 2010
Sy, Have you used the tube? From What I understand, it is the same as the EF86 with a rimlock base, and the EF86 is a relatively well liked tube, no?

About it being incomplete, I did think they looked a bit simple, but not having any real experience with phono stages, I couldn't really tell. What is incomplete about them?
  Reply With Quote
Old 29th March 2011, 11:09 PM   #5
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 1
Well, you'd need at least one more stage and possible a buffer to bring the signal up to line level and drive volume controls or interconnects.

The characteristics of the EF40 aren't the same as EF86, but are in the ballpark. Unfortunately, the EF86 isn't very quiet either (see, for example, the measurements in Frank Bloehbaum's article in Linear Audio Vol 0).

Take a look at my article on MC phono stages ("His Master's Noise")- it's perhaps not the stage you'd want to build, being rather complex, but you can get a sense of the sorts of design analysis you'll need to do. This is also covered very well in Morgan Jones's "Valve Amplifiers," and in a more qualitative way in Allen Wright's Preamp Design Cookbook.
__________________
And while they may not be as strong as apes, don't lock eyes with 'em, don't do it. Puts 'em on edge. They might go into berzerker mode; come at you like a whirling dervish, all fists and elbows.
  Reply With Quote
Old 30th March 2011, 08:37 AM   #6
diyAudio Member
 
Join Date: Apr 2010
My Mullard book gives the characteristics of the EF40 and EF86 as so similaras to to make no difference in practice. Noise figures are not quoted but I always understood the EF86 was the same valve in a B9A envelope. The EF40 was widely used in the late 40`s / early 50`s for low level preamps before the rush to standardise on B9A valves for signal purposes.
Two of the circuits given use the valve in Triode mode, this gives characteristics not far off an ECC82 / 12AU7 though not identical. I don`t know what this does for the noise but certainly a properly designed Triode preamp is going to be quieter than an EF40 / 86.
However, given that you have the valves and the rest of the components are cheap, why not give it a go, you may like the result. As already mentioned you will need additional gain / buffering to drive most amps though.

Barry
  Reply With Quote
Old 30th March 2011, 10:26 AM   #7
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 1
An old timers' trick to get better noise performance out of EF86 is to use the screen grid as the anode. It's still not as quiet as later, better tubes, but more quiet than EF86 run in pentode. As a more conventional triode (screen and plate connected), it's more linear than 12AU7/ECC82, but the gain is low and the noise is still not great.
__________________
And while they may not be as strong as apes, don't lock eyes with 'em, don't do it. Puts 'em on edge. They might go into berzerker mode; come at you like a whirling dervish, all fists and elbows.
  Reply With Quote
Old 30th March 2011, 10:46 AM   #8
diyAudio Member
 
Join Date: Apr 2010
Quote:
Originally Posted by SY View Post
An old timers' trick to get better noise performance out of EF86 is to use the screen grid as the anode. It's still not as quiet as later, better tubes, but more quiet than EF86 run in pentode. As a more conventional triode (screen and plate connected), it's more linear than 12AU7/ECC82, but the gain is low and the noise is still not great.
I`d not heard of that - interesting. I do know that the noise figure on a tape replay amp was some 6db better when the first stage EF86 was replaced with an ECC83.

As an aside , do you know whether the older EF37A was actually quieter than the EF40 / 86? The 1953 EMI BTR2 used them in the replay amp even though the later valves were available.
  Reply With Quote
Old 30th March 2011, 10:49 AM   #9
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 1
Nope, never used an EF37.

The screen trick was unintentionally revived recently- there's an article in Linear Audio Vol 0 where that's used as the bottom tube in a hybrid cascode.
__________________
And while they may not be as strong as apes, don't lock eyes with 'em, don't do it. Puts 'em on edge. They might go into berzerker mode; come at you like a whirling dervish, all fists and elbows.
  Reply With Quote
Old 31st March 2011, 06:28 PM   #10
diyAudio Member
 
Join Date: May 2010
thanks for the feedback. It sounds like this might be a viable project, if only for experimentation, but only after I have some better design skills
  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
MC preamp kit Blnd2Spll Analogue Source 1 7th February 2011 02:10 AM
Hampton MC preamp vacuumhead Tubes / Valves 2 11th November 2010 03:14 PM
Schematic - B & K MC-101 Sonata (Pro-MC-10) Preamp dtm1962 Solid State 0 13th June 2006 08:46 PM
MC phono preamp Vortex Tubes / Valves 29 29th March 2004 11:39 AM
MC preamp KenP Solid State 2 17th December 2002 01:41 AM


New To Site? Need Help?

All times are GMT. The time now is 06:05 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