Need Help Biasing Marshall dsl 100 (1999)

[joedell71]

Hello

I posted on this forum a while back while changing the tubes in my Marshall dsl 100 head. I changed the tubes and set the bias at the test points in the back of the head. I could never get the Mvs to stay the same after I set them. I would set them then play a little, check them and they would be different. I was setting it around 78Mvs which was recommended by someone on this forum. I did not use a resistor in the speaker jack when I was Biasing. I set it plugged in to the speaker and unplugged from the speaker and the values still jumped around. Do I need to have the resistor to properly bias. If so what are the values I need? i run the amp at 8 ohms and it's a 100 watt amp so do I need an 8ohm 100 watt resistor.I did finally get it to sound half way decent but I want to know if I can get it to sound better. Any help would be greatly appreciated.

Joe

[izzybell2810]

No need to buy a resistor, the speaker is fine, although I wouldn't advise you run your amp without a load present (i.e. th speaker connected). you say the voltage is moving about, it will with a signal applied. Leave it to idle and check the dissipation. EL34's? 20 watts static diss per tube MAX. If you're not happy with the sound (and I never met a guitarist who was including myself) then have a twiddle, see what sounds best for you, then check how the amp is running. If you like the sound when it's running a little on the hot side, fine, just meANS you'll change the tubes sooner.

Dave.

[Lee W]

This site goes through biasing on the DSL/TSL

http://www.eurotubes.com/euro-Marshall-DSLTSLV.htm

[joedell71]

No need to buy a resistor, the speaker is fine, although I wouldn't advise you run your amp without a load present (i.e. th speaker connected). you say the voltage is moving about, it will with a signal applied. Leave it to idle and check the dissipation. EL34's? 20 watts static diss per tube MAX. If you're not happy with the sound (and I never met a guitarist who was including myself) then have a twiddle, see what sounds best for you, then check how the amp is running. If you like the sound when it's running a little on the hot side, fine, just meANS you'll change the tubes sooner.

Dave.

Thanks for the reply. One question though what is 20 watts static diss is this dissipation and how do I measure it. I have been measuring the millivolts when biasing. Sorry I'm not very tech savvy so if you could explain this a little better it would be greatly appreciated.(and you were right I'm always searching for ways to improve my tone)

[bnwitt]

the problem with that video is it doesn't even mention Plate voltage. Dissipation is the wattage the tubes are pulling. In order to calculate dissipation you need both the milliamps and the plate voltage. Volts times amps is watts and that is what you need to know. On this amp you are reading the milliamps in millivolts across a 1 ohm resistor for each pair of tubes so you must half the reading to get per tube milliamps. That is assuming the two tubes in the pair are drawing equal current which may or may not be the case. To read more about the bias process go here:

http://www.duncanamps.com/technical/lvbias.html

[Enzo]

And don't play through teh amp while setting the bias, after all the bias is IDLE current.

[dave7145]

volume

this may be a dumb question, but i just can't find an answer. should the volume be turned up or down during biasing. as much information about the position of the controls would be great.

thanks guys

btw, great forum