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Biasing a Marshall DSL50 amp


 
5/9/2004 2:07 AM
muletone
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Biasing a Marshall DSL50 amp
Hello,  
 
I've got a JCM2000 DSL50 head that I need to re-bias. I own a Alessandro bias meter that has two sockets that plug into the amps power sockets and then the tubes on top of those.  
 
However, the DSL amp has a 3 prong deal with two little plastic screws to adjust the bias. Do I need a special guage or something? With the Alessandro in the sockets, I can't get the bias any higher than about 23ma on each side. That's max. It's doesn't seem right and it sounds terrible.  
 
Has anybody biased one of these amps?  
 
Thanks
 
5/10/2004 4:19 PM
PAULH
The center pin is ground and the outside pins are your test points (1 ohm resistors between cathodes and ground). Marshall sets them at 45mv which is to hot in my opinion. I set them for 37mv. If you can't get above 23ma, I'd say you've got something wrong i.e. bad tubes? Keep in mind these trim pots are backwards. To raise the idle current you turn the pots ccw
 
 
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5/10/2004 10:48 PM
Enzo
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SOmething else is going on in there.
 
5/11/2004 5:13 AM
muletone
I think I'll drop some new tubes in and try to bias them with a DC Volt meter like Paul said. If it doesn't work then, I'll take it to the shop.  
 
Thanks for the help.  
 
Muletone
 
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