The Official Marshall DSL40c Information Thread

[Swede]

Hey Liquor, talk to John H. he is the member from Australia that helped me with my 1x12 cab

 

[Len]

Now.... one thing I'd like to see on this amp that they left out... an "overall Master Volume" (Or Effects Loop return Level)... anyone got any thoughts on this item? I've not seen a schematic floating around yet for it.

I use an Unleash to get that single volume, and solo boosting.

 

[3dognate]

I use an Unleash to get that single volume, and solo boosting.

Those cost more than I paid for my DSL40C.... (But it is a little bit of a cool product too...)
I

 

[jimmyjames]

I recommend getting a good attenuator. One with variable resistance settings for both input and output. Get those power tubes earning their keep and use it with anything else the future brings

 

[USAPatriot]

So where are we with someone trying 6550's in their 40C? Anyone? Bueller? Bueller?
I'd give it a shot but can't afford a set of tubes any time soon. -Rod-

 

[MarshallDog]

So where are we with someone trying 6550's in their 40C? Anyone? Bueller? Bueller?
I'd give it a shot but can't afford a set of tubes any time soon. -Rod-

I want to try it and will buy the tubes but I have been wondering about:
1. Which two bias resistors need to be changed seeing as there are two bias pots and anyone have any idea on what value to try.
2. Any other components that need to be changed?
3. What 6550's are recommended, JJ's, Tung-Sol's, I'm not interested in paying 100 bucks a piece for =C=! Ting-Sols seem to have the best review at The Tube Store.

It appears there it takes a bit to change these tubes so I am really thinking about it before I decided to the plung, it's not a quick switch back.

 

[3dognate]

I want to try it and will buy the tubes but I have been wondering about:
1. Which two bias resistors need to be changed seeing as there are two bias pots and anyone have any idea on what value to try.
2. Any other components that need to be changed?
3. What 6550's are recommended, JJ's, Tung-Sol's, I'm not interested in paying 100 bucks a piece for =C=! Ting-Sols seem to have the best review at The Tube Store.

It appears there is a bit tomt yang these tubes so I am really thinking about it before I decided to the plung, it's not a quick switch back.

You might need to change the negative feedback resistor to a more appropriate value.

 

[50WPLEXI]

Thinking about changing the stock EL34's that came with my DSL 40C. I just checked the stock BIAS settings. Looks like I'm getting 25.0ma for one side, 27.5 for the other.

By reading through this thread looks like you all are setting the BIAS between 36-38ma. Does Marshall just set the BIAS this cold from the factory?

I know it saves on tube life, but just wanted to hear what you all have to say, thanks.

 

[MarshallDog]

Thinking about changing the stock EL34's that came with my DSL 40C. I just checked the stock BIAS settings. Looks like I'm getting 25.0ma for one side, 27.5 for the other.

By reading through this thread looks like you all are setting the BIAS between 36-38ma. Does Marshall just set the BIAS this cold from the factory?

I know it saves on tube life, but just wanted to hear what you all have to say, thanks.

I set mine at 70% max dissipation and to do that you need to measure the plate voltage and use the good old formula P=IV to ensure the highest bias current setting without exceeding 70% power dissipation. A bias mA setting value without the voltage means nothing to me...

 

[MarshallDog]

You might need to change the negative feedback resistor to a more appropriate value.

Would you say lower? If so, I have already lowered mine to 47K and love the tone now

 

[50WPLEXI]

I set mine at 70% max dissipation and to do that you need to measure the plate voltage and use the good old formula P=IV to ensure the highest bias current setting without exceeding 70% power dissipation. A bias mA setting value without the voltage means nothing to me...

I'll check on the plate voltage. But doesn't that seem low for a BIAS setting?

 

[MarshallDog]

I'll check on the plate voltage. But doesn't that seem low for a BIAS setting?

Not if the plate voltage is high but i do believe amp mfgs set the bias low to make the tubes last longer getting them past the warranty period.

 

[Mesa100w]

I have a Marshall DSL 40 c,I did the c19 mod,and upgraded the speaker with an EV SRO 12,the gain channel sounds great now,but just after the warranty expired the clean channel is all fuzzy and the output is low,does anyone know of the whereabouts of a schematic for this amp? I used to have an older 50 watt plexie head back in the "day" when you could buy a used one for $400...I wanted to get back into the Marshall sound again but I'm somewhat letdown,if anyone could be of help please let Me know...

Thanks

 

[USAPatriot]

I want to try it and will buy the tubes but I have been wondering about:
1. Which two bias resistors need to be changed seeing as there are two bias pots and anyone have any idea on what value to try.
2. Any other components that need to be changed?
3. What 6550's are recommended, JJ's, Tung-Sol's, I'm not interested in paying 100 bucks a piece for =C=! Ting-Sols seem to have the best review at The Tube Store.

It appears there it takes a bit to change these tubes so I am really thinking about it before I decided to the plung, it's not a quick switch back.

One thing to note is the different functionality of the 6550 versus the EL34's and 6CA7's. The stock EL34 tubes use Pin 1 as a suppressor. My guess is that this is what allows them to be switched between Triode and Pentode modes. (If I'm wrong, someone please correct me)
The 6550's Pin1 seems to be unused, at least according to the diagram I looked at last night. Other than that they seem to be alike. I'll try to post an A/B of the specs here later today.

As for the cost, at Tube Depot, the EH6550's are 10 bucks more than the EH-EL34B's. I did not look at other brands. On the plus side, the photo of the EH6550 showed a bias point of 40, which is in the wheelhouse for the 40C, if a tad hot. I'm sure it could be turned down. -Rod-

 

[MarshallDog]

One thing to note is the different functionality of the 6550 versus the EL34's and 6CA7's. The stock EL34 tubes use Pin 1 as a suppressor. My guess is that this is what allows them to be switched between Tetrode and Pentode modes. (If I'm wrong, someone please correct me)
The 6550's Pin1 seems to be unused, at least according to the diagram I looked at last night. Other than that they seem to be alike. I'll try to post an A/B of the specs here later today.

As for the cost, at Tube Depot, the EH6550's are 10 bucks more than the EH-EL34B's. I did not look at other brands. On the plus side, the photo of the EH6550 showed a bias point of 40, which is in the wheelhouse for the 40C, if a tad hot. I'm sure it could be turned down. -Rod-

Good point about the pentode mode, that slipped my mind, maybe someone else can chime in and help clarify/verify this???

 

[USAPatriot]

OOPS! I had to edit my previous post as it is TRIODE (not Tetrode) and Pentode modes. Sorry. -Rod-

 

[wolfpack]

Looking for help to understand biasing this amp with my compu-bias.
It displays plate voltage as Vp, cathode current as ik & wattage as W.
I have seen others here using multi-meters recommend around 38mv as a good range with the stock Marshall or JJ EL-34L tubes.
What is the mv reading providing info for ?
Is that for cathode current (ik) ?

I've emailed the manufacturer & am waiting for a response, but thought I would try here as well.

Thanks

 

[mickeydg5]

Looking for help to understand biasing this amp with my compu-bias.
It displays plate voltage as Vp, cathode current as ik & wattage as W.
I have seen others here using multi-meters recommend around 38mv as a good range with the stock Marshall or JJ EL-34L tubes.
What is the mv reading providing info for ?
Is that for cathode current (ik) ?

I've emailed the manufacturer & am waiting for a response, but thought I would try here as well.

Thanks

Yes, the mV reading converts directly to mA when measured across a precision 1 ohm cathode resistor. That is the cathode current "Ik".

 

[Micky]

The DSL40c has built-in resistors for setting the bias.
When you read the millivolts across these resistors, it is a direct correlation to bias current. i.e. 35mv reading results in 35ma bias current.

In order to read current directly, one must interrupt the circuit and place a current meter in series. By using the bias shunt resistors, you eliminate that need and can bias the power tubes in a much safer fashion.

The very first page of this thread describes the process to set bias using only a multi-meter.

Here is a wiki describing the use of a shunt:
http://en.wikipedia.org/wiki/Shunt_(electrical)
Scroll down to the last part.

A 1-ohm resistor as a shunt has a direct 1:1 relationship (correlation) to the amount of current being passed thru it. If the voltage drop (difference) across the resistor is 35mv, then 35ma of current is going thru the resistor. If you were using a 10-ohm resistor, you would measure 350mv across the resistor to achieve the same 35ma current load.

Marshall uses these resistors to provide a much safer method to set the bias, at the test points you have a very low voltage (in reference to ground) preventing potential electrical hazards. There is no need to interrupt the circuit to measure this value, by using a bias 'probe' or other type of device. There is no need to remove tubes and introduce any danger of electrocution with the shunt resistor method Marshall provides.

If you DO use some sort of other device, extreme care must be taken to insure the manufacturers instructions are followed TO THE LETTER and that you turn off all power BEFORE connecting or disconnecting the device.

Anywhere between 30 and 40 ma is a good range for this amp.

 

[armandodiaz]

C4 and C19....

I know there's been a lot of testing with different cap values. Has anyone come up any good results?

On channel one. I barely have the tremble on 2. So I would like to give myself a little more breathing room.

On channel two. I already have C19 clipped and it sounds "ok", but might sound better with an actual cap installed.