Marshall DSL40C No reading when checking the BIAS

[Zedi]

Hi I'm a newbie here I have just purchased a Marshall DSL40C 2015 Model Limited edition white made in Vietnam from ebay. It was sold as making a crackling noise when you move the vol knob. When I plugged it in to test it, it was making a loud humming/crackling sound so after some research I thought must be the EL34 Valves so did the old tap thing and nothing. The valves were both glowing so I thought I would check the bias on the old multi meter. So I connected the black to the middle on Con 5 and red to the left the the right side meter is set to 200mv but the reading on the meter stays at 0 and sometimes fluctuates to 1. It's a nice amp and I would love to keep it but I have until the 26th October to return it if I am not happy so I just want to explore every avenue before I decide on the former. My question is has anybody ever experienced this before where the bias reads zero?

Thanks for your help in advance.

 

[Leonard Neemoil]

Welcome to the forum.

Nice amps. I missed out on one of those a couple of years ago.

I have a 2016(or 2013?) DSL 40 C and it's been a couple of years since I biased it, but I'm pretty sure you're supposed to use the milliamp setting for the bias, not mV.

 

[Zedi]

Welcome to the forum.

Nice amps. I missed out on one of those a couple of years ago.

I have a 2016(or 2013?) DSL 40 C and it's been a couple of years since I biased it, but I'm pretty sure you're supposed to use the milliamp setting for the bias, not mV.

Sorry that's what I meant the milliamp is what I used

 

[Georgiatec]

Hi I'm a newbie here I have just purchased a Marshall DSL40C 2015 Model Limited edition white made in Vietnam from ebay. It was sold as making a crackling noise when you move the vol knob. When I plugged it in to test it, it was making a loud humming/crackling sound so after some research I thought must be the EL34 Valves so did the old tap thing and nothing. The valves were both glowing so I thought I would check the bias on the old multi meter. So I connected the black to the middle on Con 5 and red to the left the the right side meter is set to 200mv but the reading on the meter stays at 0 and sometimes fluctuates to 1. It's a nice amp and I would love to keep it but I have until the 26th October to return it if I am not happy so I just want to explore every avenue before I decide on the former. My question is has anybody ever experienced this before where the bias reads zero?

Thanks for your help in advance.

Nine year old amp off Ebay? First job change ALL the tubes for known good ones or new. You have to assume the seller put known junk in there. Set your multimeter to MA not MV to set bias.

 

[PelliX]

Nine year old amp off Ebay? First job change ALL the tubes for known good ones or new. You have to assume the seller put known junk in there. Set your multimeter to MA not MV to set bias.

^ This. In addition, crackling when turning the volume pot could indicate DC leaking to there. Any chance of at least a gutshot?

 

[neill]

First of all, you're trying to measure the milliamps through the valves BUT the way it's done is there's a 1ohm resistor inline with the cathode to ground connection and you measure the voltage drop across that resistor. As it's 1 ohm, 1ma through the valves will measure as 1mv on your meter so mv = ma. Don't set your meter to ma: it won't return any meaningful reading and you may damage the valves trying to adjust the bias without correctly measuring the effect of the adjustment. If there's sound coming from the amp, there must be current flowing through the valves. I'd double check your connection from the probes to con5: the pins might be oxidised. If the pins are close together, it's easy to short them out: won't cause any harm but your meter will read 0.

 

[Micky]

Use DC mv scale.
Bias should be 30-something millivolts DC, it is very important to balance the finals rather than set to some pre-determined arbitrary value. For example, set to 35.1 each side...

 

[Tederoni]

Hi I'm a newbie here I have just purchased a Marshall DSL40C 2015 Model Limited edition white made in Vietnam from ebay. It was sold as making a crackling noise when you move the vol knob. When I plugged it in to test it, it was making a loud humming/crackling sound so after some research I thought must be the EL34 Valves so did the old tap thing and nothing. The valves were both glowing so I thought I would check the bias on the old multi meter. So I connected the black to the middle on Con 5 and red to the left the the right side meter is set to 200mv but the reading on the meter stays at 0 and sometimes fluctuates to 1. It's a nice amp and I would love to keep it but I have until the 26th October to return it if I am not happy so I just want to explore every avenue before I decide on the former. My question is has anybody ever experienced this before where the bias reads zero?

Thanks for your help in advance.

The crackling is probably dirt in the pot. Get some Deoxit spray. It's very good at cleaning. It's super simple to clean pots if you can get to them straight away. Otherwise, take out the board. I'd clean all of them and all of the plugs while you're there with it. It saves you from taking it apart so soon in the future. Good luck.