807 E-Linear - diyAudio
Go Back   Home > Forums > Amplifiers > Tubes / Valves

Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

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 8th January 2007, 06:56 PM   #1
Fuling is offline Fuling  Sweden
diyAudio Member
 
Join Date: Aug 2001
Location: Sweden (Mora)
Default 807 E-Linear

A while ago I promised my brother to help him build a tube amp.
Since we were on a budget, we decided to use those 18 bucks Edcor OPTīs and a pair of 807īs.
After a few detours I finally got a prototype running yesterday,
but to my disappointment it didnīt sound as good as I had expected. The output tubes were running in UL mode with CFB from the OPT secondary, and obviously this wasnīt enough to get the output impedance low enough.

Since my brothers speakers are quite insensitive triode connection was never an option and I didnīt want to surrender to global NFB, I came up with the (seemingly) great idea to connect the input tubes plate resistors to the UL taps rather than to B+. I believe this is called E-linear. Iīve read that this topology works best with high impedance driver stages, so I removed the cathode bypass caps for the input stage.

The bass response immediately got much better, not "floppy" as it was before.
This drawing shows how the amp is wired today:

Any obvious mistakes here?
The amp sounds really good, but I havenīt done any measuerements yet.
Attached Images
File Type: jpg 807e-l.jpg (33.6 KB, 1803 views)
  Reply With Quote
Old 8th January 2007, 11:57 PM   #2
diyAudio Member
 
Join Date: Jul 2003
Location: Ann Arbor, MI
Hey-Hey!!!,
Looks good to me. I prefer pentodes for the input stage...actually cascodes but your ears are the final arbiter on that one. The pentode plate returns more NFB as it doesn't really care what the voltage is( like a triode ).

It is indeed called E-Linear. That circuit is different enough to deserve its own name.
cheers,
Douglas
__________________
the Tnuctipun will return
  Reply With Quote
Old 9th January 2007, 04:33 AM   #3
arnoldc is offline arnoldc  Philippines
diyAudio Member
 
Join Date: Apr 2003
Location: Makati
Send a message via Yahoo to arnoldc
Is this topology specifically made for plate loaded input tubes?

What if I have a CCS on the input tube plate? Will that make a difference?
  Reply With Quote
Old 9th January 2007, 04:39 AM   #4
Sheldon is offline Sheldon  United States
diyAudio Member
 
Join Date: Dec 2003
Location: San Diego
If you're in to mode of experimentation, here's another partial feedback approach you might want to look at: http://www.tubeaudio.8m.com/807/807.html
If you search under RH807, you'll find some examples.

Sheldon
  Reply With Quote
Old 9th January 2007, 07:44 AM   #5
Fuling is offline Fuling  Sweden
diyAudio Member
 
Join Date: Aug 2001
Location: Sweden (Mora)
What Iīve come up with here seems to be a mix between Pete Milletts E-linear amp and Alexīs RH807.
Cost and simplicity has high priority, thatīs why I use a dual triode on the input. (Well, actually itīs because I didnīt plan to use this kind of feedback from the beginning).
Can I expect huge improvements by changing to pentodes (6AU6 or something)?

Iīm going to run some measurements on the prototype tonight, Iīm not sure that my driver stage is capable of pushing the output tubes to full power.
  Reply With Quote
Old 9th January 2007, 09:16 AM   #6
diyAudio Member
 
jan.didden's Avatar
 
Join Date: May 2002
Location: Great City of Turnhout, Belgium
Blog Entries: 7
Default Re: 807 E-Linear

Quote:
Originally posted by Fuling
A while ago I promised my brother to help him build a tube amp.
Since we were on a budget, we decided to use those 18 bucks Edcor OPTīs and a pair of 807īs.
After a few detours I finally got a prototype running yesterday,
but to my disappointment it didnīt sound as good as I had expected. The output tubes were running in UL mode with CFB from the OPT secondary, and obviously this wasnīt enough to get the output impedance low enough.

Since my brothers speakers are quite insensitive triode connection was never an option and I didnīt want to surrender to global NFB, I came up with the (seemingly) great idea to connect the input tubes plate resistors to the UL taps rather than to B+. I believe this is called E-linear. Iīve read that this topology works best with high impedance driver stages, so I removed the cathode bypass caps for the input stage.

The bass response immediately got much better, not "floppy" as it was before.
This drawing shows how the amp is wired today:

Any obvious mistakes here?
The amp sounds really good, but I havenīt done any measuerements yet.

I think if you decouple the 10 ohms cathode resistor you double the output power.

Jan Didden
__________________
I won't make the tactical error to try to dislodge with rational arguments a conviction that is beyond reason - Daniel Dennett
Check out Linear Audio Vol 7!
  Reply With Quote
Old 9th January 2007, 10:50 AM   #7
Fuling is offline Fuling  Sweden
diyAudio Member
 
Join Date: Aug 2001
Location: Sweden (Mora)
The 10 ohm resistor is only there to measure the voltage drop (bias current) across, it shouldnīt affect the output power...?
  Reply With Quote
Old 9th January 2007, 10:56 AM   #8
diyAudio Member
 
jan.didden's Avatar
 
Join Date: May 2002
Location: Great City of Turnhout, Belgium
Blog Entries: 7
Quote:
Originally posted by Fuling
The 10 ohm resistor is only there to measure the voltage drop (bias current) across, it shouldnīt affect the output power...?

The 10 ohms doesn't know this...

Fact is that the signal voltage across the 10 ohms is about equal (even more) then across the speaker load because they carry the same signal current. So you lose half your power. Just put a cap across it, you still have the DC bias but now all the signal is across the speaker.

Jan Didden
__________________
I won't make the tactical error to try to dislodge with rational arguments a conviction that is beyond reason - Daniel Dennett
Check out Linear Audio Vol 7!
  Reply With Quote
Old 9th January 2007, 11:26 AM   #9
diyAudio Member
 
Circlotron's Avatar
 
Join Date: Jun 2002
Location: Melbourne, Australia
Default nahhhh....

The 8 ohm winding is coupled to the primary winding so the bottom of the 10R resistor is kind of bootstrapped. In any case, the current available from the transformer secondary is [cathode current variation] x [turns ratio].
__________________
Best-ever T/S parameter spreadsheet.
http://www.diyaudio.com/forums/multi...tml#post353269
  Reply With Quote
Old 9th January 2007, 11:45 AM   #10
Fuling is offline Fuling  Sweden
diyAudio Member
 
Join Date: Aug 2001
Location: Sweden (Mora)
I agree with Circlotron, the 10 ohm resistor is in series with the primary winding rather than with the secondary winding.
It drops about 0,65VDC at idle and perhaps 1Vpp at max output power, a very small fraction of the total plate swing.
  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
linear pot east electronics Solid State 4 9th August 2008 01:34 PM
Linear PS help ashley_kitty Power Supplies 2 16th May 2007 12:00 AM
Need help with linear PS tonyptony Power Supplies 33 14th April 2006 09:37 AM
Help with Linear PSU meta Parts 26 19th March 2003 03:56 PM


New To Site? Need Help?

All times are GMT. The time now is 02:12 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright Đ1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2