Trouble with the bias B&K ST140 - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

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 20th September 2009, 10:00 PM   #1
diyAudio Member
 
Join Date: Feb 2005
Location: ny
Default Trouble with the bias B&K ST140

Hey all,
I'm having trouble biasing my ST-140.
Prelude, I've rebuilt a Sansui au-999 and others so I kinda know my way around.
I have the schematics
As per the instructions I got from B&K remove the + rail fuse attach dvm set to milliamps (fluke77) adjust p2 to 200 milliamps.
On one channel I can't adjust it past 35ma, the other just pegs the meter to OL
then drops after power off.

This happened on the 999 and I had to replace the driver tranistor, is this the same deal?

BTW the amp plays fine and sounds good, I just want to make sure it's in spec.
and not about to blow the outputs, as they are Unobtainium (I replaced them about 12 years ago).

thanks.
mdr
  Reply With Quote
Old 21st September 2009, 12:58 AM   #2
bountyh is offline bountyh  United States
diyAudio Member
 
Join Date: Sep 2009
Post a schematic of the output and bias chain?
  Reply With Quote
Old 21st September 2009, 01:12 PM   #3
diyAudio Member
 
Join Date: Feb 2005
Location: ny
Here you go:
Click the image to open in full size.
Thanks.
mdr
  Reply With Quote
Old 21st September 2009, 05:21 PM   #4
diyAudio Member
 
Join Date: Mar 2005
Location: California
the bias is controlled by the voltage dropped across P2 by the current set by the constant current source consisting of Q10/R9/the LED

so check those parts and voltages on them.

I'd say compare channels but it sounds like both channels are wrong, still it can't hurt to compare

oh and other things could cause your problem, output MOSFETS for one
  Reply With Quote
Old 22nd September 2009, 06:29 PM   #5
diyAudio Member
 
Join Date: Feb 2005
Location: ny
Thanks I'll check those.
mdr
  Reply With Quote
Old 23rd September 2009, 03:05 PM   #6
diyAudio Member
 
Join Date: Feb 2005
Location: ny
OOOPS.
I had the probes in the wrong holes on the meter
Everything works great now
I'm going to be re-caping this guy any way.
I'll post with results.
thanks again.
mdr
  Reply With Quote
Old 24th September 2009, 02:56 PM   #7
jackies is offline jackies  United States
diyAudio Member
 
Join Date: Nov 2007
Cool!
I have a st-140 too, but never messed with it. I get an occasional rustling noise in one channel, so I was thinking to recap it too. It seems to use some sort of Arcolytic nonpolar caps. What are those, some obsolete brand?

Last edited by jackies; 24th September 2009 at 02:59 PM.
  Reply With Quote
Old 24th September 2009, 03:12 PM   #8
diyAudio Member
 
Join Date: Feb 2005
Location: ny
What you see is what I got.
  Reply With Quote
Old 3rd July 2010, 12:54 PM   #9
diyAudio Member
 
Join Date: Jul 2010
This is an old thread, but I was hoping to see if you ever recapped your ST-140. I have one also and am considering some refresh work.

Brian

Quote:
Originally Posted by mdelrossi View Post
OOOPS.
I had the probes in the wrong holes on the meter
Everything works great now
I'm going to be re-caping this guy any way.
I'll post with results.
thanks again.
mdr
  Reply With Quote
Old 8th September 2010, 12:35 AM   #10
defec is offline defec  United States
diyAudio Member
 
Join Date: Jul 2004
Location: !
Hi, Does anyone happen to know where the test points are for setting the bias with this amp are? Thanks.
  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
Trying to salvage a B&K ST140 jwv3 Solid State 4 15th January 2009 11:23 PM
Trouble with unstable bias setting. ppfred Solid State 7 3rd January 2006 01:15 PM
p3a bias trouble, quick question :) Mattyo5 Solid State 13 13th May 2004 08:03 PM
bias trouble in pnp output stage Easyamp Solid State 5 17th December 2003 06:36 PM


New To Site? Need Help?

All times are GMT. The time now is 09:22 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