Help on EL84 / ecc83 SE project -very low volume - 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 5th June 2009, 08:00 PM   #1
mcgaag is offline mcgaag  Netherlands
diyAudio Member
 
Join Date: Aug 2006
Default Help on EL84 / ecc83 SE project -very low volume

I build this amp:

http://www.joddla.net/audio/6p14p/el84sexun_jpg.jpg

The amp works but the volume is very low. I mean really low, i have to put my ear next to the speaker to hear something (speakers are a pair of Fostex 94db). What could be wrong, i double checkt every connection and that seems to be in order. Is the ecc83 broken? Is this design ok? The tubes came from a working radio but are old, 20+ years minmimum.

Some advice please.

regards,
Rob
Attached Images
File Type: jpg el84sexun_jpg.jpg (65.0 KB, 667 views)
  Reply With Quote
Old 5th June 2009, 09:12 PM   #2
diyAudio Member
 
Join Date: Mar 2003
Location: Zürich
Hi Rob

I think that the best first pass in this troubleshooting is to measure all DC voltages in your amp, to check biasing of the stages. You have got a nice schematic there, so you can open it in paint and write down all DC values, and post back here. With all DC voltages I mean the voltages at the terminals of the tubes (plate, grid 2, grid 1, cathode) of each tube.
__________________
my surname is indeed 'de Best': neither misspelling nor snobbism! Ask SY!
  Reply With Quote
Old 5th June 2009, 10:24 PM   #3
diyAudio Member
 
Panicos K's Avatar
 
Join Date: Oct 2006
Your thread speaks of 12AX7,your schematic says 6N2P.Maybe you have to rewire the tube sockets for 12AX7 or use 6N2P tubes?
  Reply With Quote
Old 5th June 2009, 10:44 PM   #4
diyAudio Member
 
Join Date: Aug 2006
http://cityradio.narod.ru/spr/tubes/...hort/6n2p.html

http://tdsl.duncanamps.com/show.php?des=12AX7

Pinout looks the same. Double check you have proper voltages, make sure that you haven't accidentally shorted/touched any wires together.

I recently wired some new pickups into my nephews electric guitar, we hooked it up and NOTHING ! ! ! I was pulling my hair out. Then I realised that when I heated up the wire for soldering, it had melted through the twisted pair insulation and bonded to the other wire , causing a dead short.

Accidents happen. Double check your work.

Are your driver tubes (6N2P, or 12AX7) heaters lighting up ? Check your heater wiring ?

What did you use for a source ? CD , turntable, tuner ?

Good luck........................Blake
__________________
Keep it simple
My Page Of SV1000 and DIY Stereo Links
  Reply With Quote
Old 5th June 2009, 11:00 PM   #5
diyAudio Member
 
Join Date: Aug 2006
I just looked at your schematic again. Perhaps I'm crazy, but your grid stopper resistors on your input tubes (6n2p/12ax7) are only 82k. That seems like it would be dumping alot of your input signal to ground.

Try a 500k or 1meg resistor, or just for a quick test, unhook one side of the 82k resistor (effectively taking it out of the circuit). I bet this cures your low volume issue.

Let me know how it works out.



.........................Blake
__________________
Keep it simple
My Page Of SV1000 and DIY Stereo Links
  Reply With Quote
Old 5th June 2009, 11:09 PM   #6
diyAudio Member
 
Panicos K's Avatar
 
Join Date: Oct 2006
Maybe this can help.
Attached Files
File Type: zip rb6n2pcv.zip (14.5 KB, 76 views)
  Reply With Quote
Old 6th June 2009, 12:01 AM   #7
chrish is offline chrish  Australia
diyAudio Member
 
chrish's Avatar
 
Join Date: Oct 2003
Location: Sydney
I would also check that your input and speaker terminals are isolated from the chassis, ie they are not shorting out to ground.

Chris
  Reply With Quote
Old 6th June 2009, 03:07 AM   #8
frugal-phile(tm)
diyAudio Moderator
 
planet10's Avatar
 
Join Date: Oct 2001
Location: Victoria, BC, NA, Sol III
Blog Entries: 5
Quote:
Originally posted by Nihilist
in. Perhaps I'm crazy, but your grid stopper resistors on your input tubes (6n2p/12ax7) are only 82k.
Grid Leak resistor (no grid stopper in this circuit). It is quite common to use 100k pot in this position, so 82k fixed shouldn't be a hardship.

dave
__________________
community sites t-linespeakers.org, frugal-horn.com, frugal-phile.com ........ commercial site planet10-HiFi
p10-hifi forum here at diyA
  Reply With Quote
Old 6th June 2009, 11:38 AM   #9
mcgaag is offline mcgaag  Netherlands
diyAudio Member
 
Join Date: Aug 2006
I checked the heaters and those are all ok. 6,3 Volt and they heat up nicely. Though the heater on the 12AX7 glows up bright when i turn on the amp and then glows down again to normal. I don't know if this is normal. I did pay attention to the different way the heater is connected though, so that should not be a problem, (4-5 and 9).

I also checked that input and speaker terminals are isolated from the chassis. Thats all ok to. I am sure the wiring is ok. Triple checked everything.
Here is the schematic with the pin voltage. The B+ is 252 Volt.

Thanks so far everyone.
Attached Images
File Type: jpg el84sexun_with_v.jpg (22.5 KB, 501 views)
  Reply With Quote
Old 6th June 2009, 12:25 PM   #10
diyAudio Member
 
Join Date: Mar 2003
Location: Zürich
Cathode voltages appear to be good: 1,4V on the input and 7V on the output tube. The only voltage that worries me is that 210V at the plate of the driver... that one just can't be right.

The input tube is drawing a bit more than 1,1mA (1,4V / 1k2), which is fed through the 220k resistor. The voltage drop on this resistor would therefore be about 250V, which can't be right.

I think you measured 210V at the junction of the 33k resistor and the 47uF capacitor... (1,1mA * 33k = ~40V, which subtracted from 250V would give the 210V). Furthermore, I think that your plate resistor is much lower in value than the indicated 220k... maybe you put a 22k unit there instead?
__________________
my surname is indeed 'de Best': neither misspelling nor snobbism! Ask SY!
  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
El84/6bq5/ecc83 + Ef86 = Dc Pp jackinnj Tubes / Valves 10 8th February 2014 07:01 PM
EL84 DC 10Y Project korneluk Tubes / Valves 5 19th May 2008 05:03 AM
Retubing my amp (EL84, ECC81, ECC83) - Tube recommendations? horace Tubes / Valves 18 18th December 2007 01:54 PM
SE EL84 project for my friend akimball442 Tubes / Valves 17 28th June 2007 10:04 PM
OPT Project for EL84 SE Toober Tubes / Valves 23 8th August 2006 04:31 AM


New To Site? Need Help?

All times are GMT. The time now is 04:56 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