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

Instruments and Amps Everything that makes music, Especially including instrument amps.

Blown Bluesbreaker
Blown Bluesbreaker
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 21st June 2011, 11:20 PM   #1
batsong is offline batsong  United States
diyAudio Member
 
Join Date: Jan 2008
Location: St. Louis
Default Blown Bluesbreaker

Hi. Having a problem with a Marshall reissue JTM45 Bluesbreaker combo.
What I am getting is very very little signal until volume '8' and then a buzzing harsh distortion with an almost ring modulator type quality. The volume is not all that loud. No other abnormal humming, rustling or buzzing.
I've noticed that the 2nd and 3rd preamp tubes hum loudly if place my hand near the glass, and #2 with buzz loudly if I grab the glass.
Seems like the voltages from the PS are right, so I don't know about my original idea of filter cap failure. Maybe trans or choke? Speakers are ok.
I would like to isolate the pre to see if it is there or in the power amp, but not sure how.
Any help would be greatly appreciated.
-Gabe

Schematic:
http://www.raw-sewage.net/images/bb62ri-schm1.jpg
  Reply With Quote
Old 21st June 2011, 11:37 PM   #2
gingertube is offline gingertube  Australia
diyAudio Member
 
Join Date: Oct 2004
Location: Adelaide South Oz
Gabe - to test power amp section by itself, disconnect the wire from the treble pot wiper and use that as the input - make sure the DC blocking cap C10 remains in place.

Does tremlo intensity knob position change the described behaviour at all?

Cheers,
Ian
  Reply With Quote
Old 22nd June 2011, 12:57 AM   #3
batsong is offline batsong  United States
diyAudio Member
 
Join Date: Jan 2008
Location: St. Louis
Thanks, Ian. I'll look into isolating the power amp right now.
Trem only does what it does to signal, no change for the better.
  Reply With Quote
Old 22nd June 2011, 01:08 AM   #4
batsong is offline batsong  United States
diyAudio Member
 
Join Date: Jan 2008
Location: St. Louis
Power section ok. Must be in the pre.
  Reply With Quote
Old 22nd June 2011, 02:12 AM   #5
batsong is offline batsong  United States
diyAudio Member
 
Join Date: Jan 2008
Location: St. Louis
Just remembered-when amp failed, I found that the vibrato tube was d.e.a.d. I don't know if this was concurrent with my problem though, as I have not had the vibrato connected for a long time.
  Reply With Quote
Old 22nd June 2011, 04:11 AM   #6
gingertube is offline gingertube  Australia
diyAudio Member
 
Join Date: Oct 2004
Location: Adelaide South Oz
Is it the same for both CH1 and CH2 - if so points to V2 circuitry.
else its in V1 circuitry.
Don't forget simple stuff which could cause this sort of behaviour like a volume pot which is open circuit somwhere along its input to output track such that the wiper position has to be turned up far enough to bypass the track break. I've seen this happen before.
Cheers,
Ian
  Reply With Quote
Old 22nd June 2011, 03:02 PM   #7
batsong is offline batsong  United States
diyAudio Member
 
Join Date: Jan 2008
Location: St. Louis
Thanks Ian. You pointed me in the right direction. It was the 100k resistor across V2.
  Reply With Quote

Reply


Blown BluesbreakerHide 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
Is my sub blown ? andredinatale Car Audio 4 22nd May 2011 07:24 PM
Blown TE1501DR need help mbates14 Car Audio 41 19th February 2010 03:29 PM
PPIPC1400.2 Blown mbates14 Car Audio 3 22nd January 2010 09:02 PM
Blown sub? dafish48 Car Audio 1 13th October 2006 06:21 AM
blown sub wharfrat Subwoofers 10 23rd May 2004 05:12 PM


New To Site? Need Help?

All times are GMT. The time now is 02:03 PM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.79%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright ©1999-2017 diyAudio
Wiki