Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

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

Advise for nervous EL84 user
Advise for nervous EL84 user
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
Thread Tools Search this Thread
Old 15th May 2009, 07:40 PM   #1
Opusover21 is offline Opusover21  United Kingdom
diyAudio Member
Join Date: May 2009
Default Advise for nervous EL84 user

Hi Newbie here,
I have a Tube Technology Unisis and need some help on valves. I've swaped the signal valves no problem to Brimar's.

Problem (might just be me) I have is with EL84's. It takes 8 of these and I'm currently running JJ's with no problem. I ordered some Ei valves and subsequently the amp went up in smoke, one valve seat flashed over, a few resistors taken out and a fused pin welded into one of the sockets. So I'm extremely cautious about trying anything else....I've been offered some used NOS Mullards , the Genalex mullard re-issues seem to be well respected. I'm not a valve expert and the amp needs to be biased manually...

My questions are really how do I know which valves to match the amp...I know the JJ's work so what valves work on the same spec..I know an EL84 should be the same as any other but some of the higher voltage models ...how do i make the decision?...I've seen NOS Tesla's on offer too but really dont want all the fireworks and fuss all over again. You see my dilema? I want to improve on the JJ's which I though the smaller 12AX7's were a bit thick and chesty...but I really dont want to throw away on NOS valves and then the amp goes up etc...

Any help much appreciated.
  Reply With Quote
Old 16th May 2009, 02:43 PM   #2
Funker is offline Funker  Germany
diyAudio Member
Join Date: Feb 2009
Location: Hamburg, Germany
Hi ,
you got probably a huge problem.
Before anyone can really help you to find the fault put the drawing of the amp to your thread.

But I can you give you some useful hints without seeing the drawing. I assume you got an 2x30 watter with 8 EL84 Ultralinear PP.

Pull out all valves an repair/ replace the damaged parts.

You mains voltage should be in the range of +- 10%. If you have permanent overvoltage in your sockets due to have the power transformer in close neighbarhood, connect the mains selector to 240 or 250 volts ( England turned from former 240V down to the new european 230V).

Check all voltages on the tube pins with a Multimeter. Compare the indicated voltages with those in the schematic. they should be 15 to 20% higher without valves.

Check the values of the kathode and grid resistors with an Ohmmeter. they shoud be + - 10% , and at best if they are all the same.

So if you have no voltages given in the schematic, look to the valve data sheet.


Thats all I can do for you by now,

good luck !

regards from Hamburg
Ground your devices before they ground you
  Reply With Quote
Old 16th May 2009, 02:59 PM   #3
Enzo is offline Enzo  United States
diyAudio Member
Join Date: Sep 2004
Location: Lansing, Michigan
Just my opinion, but I think you are confusing a tube failure with tube "compatibility."

Your new set of EI tubes had a bad one which burnt up. It was not due to some incompatibility, it was just a bad tube. You could just as easily have gotten a bad JJ tube. Or NOS tube for that matter.

For what it is worth, I got too many defective EI tubes in the past, so I no longer will use their products. (I operate a pro audio repair shop.)

It isn;t a matter of matching the amp to a particular brand. (Other than that you might prefer the sound o0f one over the other.) It is a matter of not having a defective tube in the bunch.
  Reply With Quote
Old 16th May 2009, 03:31 PM   #4
analog_sa is offline analog_sa  Europe
diyAudio Member
analog_sa's Avatar
Join Date: Aug 2002
Location: Cascais
Originally posted by Funker

you got probably a huge problem.

Or maybe not. As Opusover21 is not asking about the repair we should probably assume this is already taken care of.

I agree with Enzo that you probably had a defective tube. And i find it cheaper to buy NOS or used Mullards and Teles instead of cheap crap. As a tube hobbyist you should definitely invest in a good tube tester and make sure you test all tubes before plugging them in. This will also allow your own matching instead of relying on someone's word.
  Reply With Quote
Old 16th May 2009, 04:49 PM   #5
pointy is offline pointy  United Kingdom
diyAudio Member
pointy's Avatar
Join Date: Mar 2009
may be try <http://www.langrex.co.uk/sales.html>

they should be OK about testing etc.....
  Reply With Quote


Advise for nervous EL84 userHide 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

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
5W EL84 drive EL84 SE Audio_idiot Tubes / Valves 31 31st May 2012 09:38 PM
New user maxmix69 Introductions 5 23rd March 2009 01:04 PM
New User dbart43 Introductions 1 26th August 2007 07:52 PM
User name problem ralphs99 Forum Problems 6 8th July 2006 02:30 AM
New user query quickymart Digital Source 0 31st December 2004 09:16 AM

New To Site? Need Help?

All times are GMT. The time now is 06:15 AM.

Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 16.67%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Copyright ©1999-2018 diyAudio