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Author Topic: Biassing Tubes  (Read 1457 times)
Dr. Glenn
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« on: October 27, 2014, 09:07:16 PM »

Tech Topic 
Was figuring my DSL40C was sounding a bit harsh, even at low volume and gain levels. The speaker sounded like it was a puny radio speaker being driven way too hard.
I got to reading up on stuff and found the Marshall amps forum that has a forum for this amp. Seems you need to check the tubes "bias" and adjust them for approx 70% of the tubes dissipation rating. A little bit of math involved but pretty simple stuff.
To set the bias correctly you need the Plate Voltage. Most I read about were 470VDC or thereabouts. Mine was 503VDC. Might be because we use 240VAC here and the power transformer is different to US UK.
Long story short, my bias was about 47mV which means the tubes were running near 100% duty. They were also quite uneven at 47 & 43 mV. I adjusted the 2 trimmers to achieve about 35mV which brings it out to about 70% duty. This is apparently the goal 
The amp and speaker now sound much better and cleaner. None of that speaker breakup I was experiencing before  The controls respond more smoothly now too.
I've gone from sorta happy to real happy in 1 hour  Cool
Added bonus, the output tubes should last longer now as they are not being driven so hard. Hard=heat=bad  Wink
Pics later
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« Reply #1 on: October 28, 2014, 07:43:17 AM »

Nicely done... I read abotu some of that in the past but always thought it was rocket science or something...

but if you can do it without hurting yourself then..... 



 
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Dr. Glenn
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« Reply #2 on: October 28, 2014, 10:03:21 AM »


but if you can do it without hurting yourself then..... 


 

I don't get it  Huh? Grin
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Scott
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« Reply #3 on: November 03, 2014, 07:00:21 PM »

It's nice to have provisions for that kind of adjustment built in.    Then again, not having them is a good excuse for not poking around in there too much. Grin
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Dr. Glenn
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« Reply #4 on: November 04, 2014, 07:55:38 AM »

It's nice to have provisions for that kind of adjustment built in.    Then again, not having them is a good excuse for not poking around in there too much. Grin

Totally agree mate 
I say, pickups, tuners, bridges, nuts, necks & controls should be welded into guitars. Amps and speaker enclosures should be nailed shut. And what's the story with gain controls being variable between 0 & 10? Should be an ON/OFF switch 0 OR 10.
I could go on 
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Chris
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« Reply #5 on: May 19, 2015, 05:44:20 PM »

I'm good with gain either on or off.

All threads are new to me since deleting my own acct.   
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Scott
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« Reply #6 on: May 23, 2015, 10:46:32 AM »

I'm good with gain either on or off.

  Typical newbie! Cheesy Resurrects an ancient thread just so he can  Kiss up to one of the mods with a lame, "Me too!!!" comment.


 Wink Grin

...besides an ordinary switch could be a recipe for disaster.  What if it gets turned off? Huh?

You'd need one of these:
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At one time, my innate professionalism precluded my accepting remuneration for rendering services in fields where I have no particular aptitude, but once I got a little hungry, I realized it was rather pretentious of me to hold myself to a higher standard than all the other professionals.
Chris
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« Reply #7 on: May 23, 2015, 09:22:38 PM »



  Typical newbie! Cheesy Resurrects an ancient thread just so he can  Kiss up to one of the mods with a lame, "Me too!!!" comment.



TROLL!!!!!!!!!!!

(I like the on/on switch though)  TROLL!!    Wait is that a NO/NO switch? Very cool...one time at band camp there was this guy and........TROLL!
« Last Edit: May 23, 2015, 09:24:10 PM by Chris » Logged
Scott
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« Reply #8 on: May 24, 2015, 10:03:18 AM »


TROLL!!!!!!!!!!!

(I like the on/on switch though)  TROLL!!    Wait is that a NO/NO switch? Very cool...one time at band camp there was this guy and........TROLL!

 THAT'S IT, MONKEY-ARM!!!  Shocked



I'M REPORTING YOU TO THE MODS!!! 

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At one time, my innate professionalism precluded my accepting remuneration for rendering services in fields where I have no particular aptitude, but once I got a little hungry, I realized it was rather pretentious of me to hold myself to a higher standard than all the other professionals.
Chris
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« Reply #9 on: May 24, 2015, 11:17:49 AM »

lol- reminds me of the guys that showed up at The Who concert back in the 80's.

Something to do with Quadrophenia  Huh?
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Chris
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« Reply #10 on: May 24, 2015, 11:20:18 AM »

Hmmm interesting...

http://www.quadrophenia.net/


Maybe I should listen to it. 
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Scott
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« Reply #11 on: May 24, 2015, 06:57:40 PM »

Mod fashion (minus the scooters) was in vogue around here for a short while, back in the mid-sixties. I didn't know about the scooters until the record came out. Huh?

The record was supposed to be in quadraphonic, but ended up with a crappy mix in stereo.
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At one time, my innate professionalism precluded my accepting remuneration for rendering services in fields where I have no particular aptitude, but once I got a little hungry, I realized it was rather pretentious of me to hold myself to a higher standard than all the other professionals.
Dr. Glenn
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« Reply #12 on: May 27, 2015, 01:24:36 AM »

+1  Grin
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Dr. Glenn
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« Reply #13 on: May 27, 2015, 01:28:26 AM »

I remember that my brother bought a quadraphonic when they first hit here. Probably early 70's 
The problem was that there were no quad records to play on it  Grin
From memory it came with a LP in quad. I still remember one of the songs on it was "LA International Airport". That should help date the quadraphonic.
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Scott
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« Reply #14 on: May 27, 2015, 03:05:21 PM »

All I remember is a lot of hype.  Grin 
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At one time, my innate professionalism precluded my accepting remuneration for rendering services in fields where I have no particular aptitude, but once I got a little hungry, I realized it was rather pretentious of me to hold myself to a higher standard than all the other professionals.
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