EF80 vs EF86 - 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 11th April 2008, 11:47 AM   #1
diyAudio Member
 
Join Date: Mar 2008
Default EF80 vs EF86

Hi.

I will build the schematics below

http://diyaudioprojects.com/Schemati...-Schematic.htm


I have though a couple of EF80. Is it possible to just swap the EF86 with EF80???
  Reply With Quote
Old 11th April 2008, 12:18 PM   #2
diyAudio Member
 
Tubes4e4's Avatar
 
Join Date: Jul 2005
Location: Leverkusen
Default Re: EF80 vs EF86

Quote:
Originally posted by newbadboy
Hi.

I will build the schematics below

http://diyaudioprojects.com/Schemati...-Schematic.htm


I have though a couple of EF80. Is it possible to just swap the EF86 with EF80???
No, it is definitely not possible.

The EF86 works under extreme current trickler conditions in that Mullard 3-3 circuit, see plot available here. While EF80 / 6BX6 as a typical RF/IF stage pentode is designed for working with much more current going. Running it at such very low cathode currents will harm its cathode and is not recommended: According to my TFK handbook, standard EF80 doesn´t sport a "zwischenschichtfreie Kathodenbeschichtung", which means, an intermediate layer in the cathode coating will build up when the tube is used at very low (or none) cathode current going. This intermediate layer building up will harm emission capability of the cathode coating.

Besides that, characteristics of EF86 and EF80 are so different, that I doubt EF80 would work satisfactory in this circuit anyway - if at all.

Regards, Tom.

P.S.: Besides that, running EF80 at more usual and appropiate currents makes it a very nice, linear, capable and cheap driver tube.
__________________
If in doubt, just measure.
  Reply With Quote
Old 11th April 2008, 12:53 PM   #3
diyAudio Member
 
Join Date: Mar 2008
<Too bad. do i have to change much in the cirquit to be able to use ef80?
  Reply With Quote
Old 11th April 2008, 02:54 PM   #4
diyAudio Member
 
Tubes4e4's Avatar
 
Join Date: Jul 2005
Location: Leverkusen
Quote:
Originally posted by newbadboy
<Too bad. do i have to change much in the cirquit to be able to use ef80?
Yes, almost everything regarding the driver stage - if you want to run EF80 under decent conditions, the special screen feed method used in the Mullard 3-3 circuit won´t do. In turn, there would be no more need to run the EL84 at such an artificially elevated cathode voltage, since the main reason to do so (screen feed voltage supply for the driver stage) is gone.

Would be simpler and more efficient to design a generic EF80/EL84 based amp just from scratch.

Tom
__________________
If in doubt, just measure.
  Reply With Quote
Old 1st February 2014, 04:06 PM   #5
jbefumo is offline jbefumo  United States
diyAudio Member
 
Join Date: May 2009
Just stumbled across this old thread . . .

Built an amp using an EF86 in the preamp, and since I had an extra hole in the chassis, and an extra EF80 laying around, I wired up an extra socket in parallel, correcting the appropriate pins, and tried comparing the circuit alternating the tubes -- both sound fine -- just did it for a few seconds, and haven't taken any measurements yet.

I'm attaching the relevant. circuit segment.

Does this look as if it will damage either the tube or any other components?

Joe



Quote:
Originally Posted by Tubes4e4 View Post
No, it is definitely not possible.

The EF86 works under extreme current trickler conditions in that Mullard 3-3 circuit, see plot available here. While EF80 / 6BX6 as a typical RF/IF stage pentode is designed for working with much more current going. Running it at such very low cathode currents will harm its cathode and is not recommended: According to my TFK handbook, standard EF80 doesn´t sport a "zwischenschichtfreie Kathodenbeschichtung", which means, an intermediate layer in the cathode coating will build up when the tube is used at very low (or none) cathode current going. This intermediate layer building up will harm emission capability of the cathode coating.

Besides that, characteristics of EF86 and EF80 are so different, that I doubt EF80 would work satisfactory in this circuit anyway - if at all.

Regards, Tom.

P.S.: Besides that, running EF80 at more usual and appropiate currents makes it a very nice, linear, capable and cheap driver tube.
Attached Images
File Type: jpg ef86-ef80.jpg (70.0 KB, 378 views)
  Reply With Quote
Old 4th February 2014, 02:53 PM   #6
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
Quote:
Originally Posted by jbefumo
Does this look as if it will damage either the tube or any other components?
In the long run you risk cathode interface problems, as Tubes4e4 said. You are also likely to be getting significantly more noise and distortion than an EF80 is capable of in the correct circuit. EF80 and EF86 are simply very different valves: they are both pentodes, both use B9A base and both have 6.3V heater but apart from that they are very different.
  Reply With Quote
Old 16th April 2014, 07:40 PM   #7
jbefumo is offline jbefumo  United States
diyAudio Member
 
Join Date: May 2009
FWIW -- I built parallel tube sockets in my prototyping chassis so I could interchange EF80 and EF86 tubes, and the EF80 sounds great, despite not having adjusted the cathode and grid resistors to more appropriate values. AND, I have it in a TINY high-power combo - - - 2XEL34 in a box smaller than a Fender Champ, and no issues with microphonics so far. It has a bit more gain than the EF86 (u 50 vs. 38, if memory serves) but also seems to have a more complex tone to my ears.

I will probably put a switch in so I can reconfigure a single socket to work with either one.

Joe

Quote:
Originally Posted by Tubes4e4 View Post
No, it is definitely not possible.

The EF86 works under extreme current trickler conditions in that Mullard 3-3 circuit, see plot available here. While EF80 / 6BX6 as a typical RF/IF stage pentode is designed for working with much more current going. Running it at such very low cathode currents will harm its cathode and is not recommended: According to my TFK handbook, standard EF80 doesn´t sport a "zwischenschichtfreie Kathodenbeschichtung", which means, an intermediate layer in the cathode coating will build up when the tube is used at very low (or none) cathode current going. This intermediate layer building up will harm emission capability of the cathode coating.

Besides that, characteristics of EF86 and EF80 are so different, that I doubt EF80 would work satisfactory in this circuit anyway - if at all.

Regards, Tom.

P.S.: Besides that, running EF80 at more usual and appropiate currents makes it a very nice, linear, capable and cheap driver tube.
  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
Ef86 trancy Tubes / Valves 44 2nd February 2012 08:38 PM
Combine EF80 with EL84 newbadboy Tubes / Valves 27 13th March 2010 06:32 PM
EL84 + EF86 takashi Tubes / Valves 10 28th March 2008 03:30 PM
EF86 Gm dsavitsk Tubes / Valves 7 31st March 2007 08:59 PM
EF86 penthode specter73 Tubes / Valves 8 7th December 2005 06:38 PM


New To Site? Need Help?

All times are GMT. The time now is 01:41 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