The Boogie Board

Discussion Forum for Mesa Boogie Products
It is currently Sat Apr 21, 2018 7:34 pm

All times are UTC - 6 hours [ DST ]




Post new topic Reply to topic  [ 3 posts ] 
Author Message
 Post subject: Bias question
PostPosted: Sun Apr 15, 2018 1:10 pm 
Offline
Mark I
User avatar

Joined: Wed Apr 27, 2016 9:46 pm
Posts: 37
I am getting a pretty good amount of hum (home, gigs and studios) that really sounds like a Bias problem in my Mark III black dot. I looked at the schematics and there is no adjustment that I see.

Is the way to adjust the bias that I am missing?

Thanks in advance for any info and help on this.

8)

_________________
'58 VOS Gibson Les Paul || 1984 Custom Stratocaster || 2014 Gibson Firebird
Vai Legacy 1 Head || Mesa 2x12 Cab || Modded Blues Jr || Boogie Mk III ||
TC electronic Delay/Reverb || Plimsoul - Xotic Wah - EP booster - CS Deja Vibe


Top
 Profile  
 
 Post subject: Re: Bias question
PostPosted: Sun Apr 15, 2018 7:40 pm 
Offline
Mark I

Joined: Sun Aug 21, 2016 10:00 pm
Posts: 23
No Bias on any Boogie I know of , could be a bad tube I would start there

_________________
Mesa MKIIb ( my first in 82 )
Mesa MK V
PRS 2 Channel H
Tonal Insanity Guitar Effects
TC Electronics Nova System
PRS Guitars


Top
 Profile  
 
 Post subject: Re: Bias question
PostPosted: Mon Apr 16, 2018 8:23 am 
Offline
Mark I

Joined: Wed Jan 31, 2018 8:32 am
Posts: 47
Bias is fixed on Boogies. Make sure you're using Mesa Power Tubes or equivalent as their bias is within required tolerance. Also check bias caps if they've never been changed. Worth doing filter caps as well as general maintenance.

Apart from that, could be a bad preamp tube. I normally tap them with something rigid and plastic like a chopstick and see if the noise gets worse, or swap with known good valves one by one.

If not, take the chassis out if you're confident to look for any obvious component that is burnt. If in doubt, get an amp tech to look at it.

Normal things to go are the 470 Ohm carbon resistors on the Power Tubes and the 680 Ohm R119 which should be replaced with a higher W version anyway as a precaution (2W or higher recommended)


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 3 posts ] 

All times are UTC - 6 hours [ DST ]


Who is online

Users browsing this forum: No registered users and 1 guest


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum

Search for:
Jump to:  
Powered by phpBB® Forum Software © phpBB Group