Re-Biasing my Marshall JCM 2000 DSL 100w. Help Please!

[nukem2k5]

I am borrowing a multimeter from the system admin here at school. I was wondering if someone could please give me specific directions on how to go about re-biasing my amp for my new tubes, or please direct me to a site with these instructions.

I'll try to post a pic later of the multimeter because I'm a little unsure of which setting to put it on. Thanks for any info you guys can give me.

Nick

[Gresh]

It needs to be set to read mV, that's millivolts. To be specific, it will be reading a negative mV rating. I believe that your amp has a 3 pin connector and two trim pots for setting the bias in the back of the amp. The black lead from the multimeter connects to the center pin. You then connect the red lead to the pin on whichever side you're adjusting. You do one side at a time. Don't take a reading off the amp until it has warmed up and is set ready to play through, ie, standby switch is not engaged. Be sure you have your speaker cabinet plugged in as well.

I think the bias on 100V marshalls, the DSL and TSL is supposed to be -90mV per side. Double check that with a tech first though, it's been a few years since I did it.

[Ant1981]

I've seen a site that says 80mV (= 80mA over 1 ohm), whatever that means, i'm not sure, do i have to use a resistor with my meter? or just probe the bias point and take readings?

[Ant1981]

I've seen a site that says 80mV (= 80mA over 1 ohm), whatever that means, i'm not sure, do i have to use a resistor with my meter? or just probe the bias point and take readings?

[Guitslinger]

Originally Posted by nukem2k5

I am borrowing a multimeter from the system admin here at school. I was wondering if someone could please give me specific directions on how to go about re-biasing my amp for my new tubes, or please direct me to a site with these instructions.

I'll try to post a pic later of the multimeter because I'm a little unsure of which setting to put it on. Thanks for any info you guys can give me.

I'm a little late to respond, but the multimeter should be set to register DC volts on the lowest setting. 90mV per side on the DSL100, or 45mV per side on the DSL50 are the factory specs, but having experimented extensively with the bias adjustments on the DSL series, I (and many others) suggest setting the bias at 80mV per side on the DSL100, or 40mV per side on the DSL50.

[renato-rt]

Originally Posted by Gresh

It needs to be set to read mV, that's millivolts. To be specific, it will be reading a negative mV rating. I believe that your amp has a 3 pin connector and two trim pots for setting the bias in the back of the amp. The black lead from the multimeter connects to the center pin. You then connect the red lead to the pin on whichever side you're adjusting. You do one side at a time. Don't take a reading off the amp until it has warmed up and is set ready to play through, ie, standby switch is not engaged. Be sure you have your speaker cabinet plugged in as well.

I think the bias on 100V marshalls, the DSL and TSL is supposed to be -90mV per side. Double check that with a tech first though, it's been a few years since I did it.

This is the best description I have found so far to adjust the bias of a Marshall JCM 2000.
I'm trying to adjust the bias of a DSL 50 and I'm still in doubt about a few things:

imageshack.us/photo/my-images/845/biasy.jpg

1. Are those points indicated by arrows the trim points for setting the bias?

2. Do I really need to measure the plate voltage, as described here:

lydian.ca/Marshall_DSL_Bias.html ?

[dragsternj]

i love when people dig out a 8 year old thread and keep on talking as if it was just stopped yesterday