Help requested for EL84 SET amp - 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 14th May 2011, 07:51 AM   #1
diyAudio Member
 
Join Date: Oct 2003
Location: lower Austria
Question Help requested for EL84 SET amp

Hi there,
my home-built EL84 SET Amp is way to low when I feed it with new model JJ EL84 or Russian EL84 equivalents (6N14N-EB), and I'd like to figure out why.
With old-stock EL84/E84L of European manufacture there are no problems. I get around 1.2 watt driving my AER-drivers in a back-loaded horn to more then satisfying levels. pic on flicr
Since my electronics knowledge is quite basic I am looking once again for help from this marvelous community of experts.
Can anybody figure out why this amp is playing (guessed) 18db lower with those 6n14n-eb valves?
Schematics are attached.
thanks, Dieter
Attached Files
File Type: pdf tmt endstufe.spl.pdf (60.4 KB, 169 views)
  Reply With Quote
Old 14th May 2011, 09:07 AM   #2
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
What is the EL84 cathode voltage with the various different valves?
  Reply With Quote
Old 14th May 2011, 12:44 PM   #3
diyAudio Member
 
Join Date: Apr 2009
I think you mean SEP don't you? EL84 is a pentode.
try a different driver tube.
  Reply With Quote
Old 14th May 2011, 01:38 PM   #4
diyAudio Member
 
Join Date: Sep 2009
Quote:
Originally Posted by oldhifiguy View Post
I think you mean SEP don't you? EL84 is a pentode.
try a different driver tube.
His schematic shows EL84 wired as a triode :-)
  Reply With Quote
Old 14th May 2011, 01:42 PM   #5
diyAudio Member
 
rvrazvan's Avatar
 
Join Date: Jul 2010
try using 6p15p. I have a Zen triode amp clone running 6p14p and had some issues with it. I was designed to be used with 6n15p not 6n14p. Don't know the details of the problem.
  Reply With Quote
Old 15th May 2011, 01:50 PM   #6
diyAudio Member
 
Join Date: Oct 2003
Location: lower Austria
with "old stock" el84 the cathode shows 9 volts.
with a new JJ EL84 it shows 16! volts. how come?
  Reply With Quote
Old 15th May 2011, 02:19 PM   #7
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
The new ones are not really EL84 but something only vaguely similar?

Or, the new ones are very gassy so have high grid current? What is the DC voltage at the control grid? This should be around zero - anything more than about +0.5V means a problem. As a temporary workaround you could reduce R8 to, say, 330K.
  Reply With Quote
Old 17th May 2011, 06:47 AM   #8
diyAudio Member
 
Join Date: Oct 2003
Location: lower Austria
Default Different EL84

I also guessed that there's a inherent difference between these tubes and that this circuit "suffers" from that difference.

they are not gassy.

Why would changing R8 make a difference, would you care to explain?

thx
  Reply With Quote
Old 17th May 2011, 07:20 AM   #9
chrish is offline chrish  Australia
diyAudio Member
 
chrish's Avatar
 
Join Date: Oct 2003
Location: Sydney
R8 is the grid leak resistor. 1M is the max specified for cathode bias for an EL84. This resistor leaks away any charge on the control grid. The temporary fix above can be done with a couple of clip leads and another resistor, say 500k-1M, in parallel. As mentioned above, measure the DC voltage on the control grid to see if this is the issue. If it is not 0 volts, it may be a grid leak problem.
  Reply With Quote
Old 17th May 2011, 08:30 AM   #10
diyAudio Member
 
Join Date: Oct 2003
Location: lower Austria
thx.
I think I found the problem. As I am not at home I looked at the pictures very closely. It looks like I soldered the grid resistor onto Pin 1 and not Pin 2 as it is supposed to be.
I made that mistake when replacing the original run-of-the-mill parts with naked foil and mills resitors.

Funny that it works at all with old-stock EL84s still some with the newer ones.
  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
FS: EL84 EI Yugoslavia & EL84 Tungsram NOS Bulk radiostar Swap Meet 3 29th January 2012 08:46 AM
Help with Decware Zen EL84 SET rvrazvan Tubes / Valves 12 7th February 2011 04:56 PM
set el84 tube amp sarrisk Tubes / Valves 15 9th September 2008 01:42 AM
What is the problem with this amp? mods requested routhun Solid State 17 11th September 2005 04:39 PM
Help requested: broken amp nowater Solid State 20 15th August 2004 07:26 PM


New To Site? Need Help?

All times are GMT. The time now is 06:11 PM.


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