HOW TO BIAS getting first tube amp!! Marshall DSL 40 EL34'S

[tman]

I need to know how you bias a tube amp?? I never did it before. Marshall said those EL 34'S in the DSL 40 are anywhere between 27-35 Mv?? Can you explain what this means to me please. And if anybody has a DSL 40 is there a bias pot in the chassis and if so how do you use that or if not how do I bias this amp if I ever change the power tubes to another brand or etc... Thanks

 

[Gearjoneser]

Re: HOW TO BIAS getting first tube amp!! Marshall DSL 40 EL34'S

I think forums make players obsess over things like tubes and bias, rather than just plugging in your perfectly good amp and playing it. However, it is a good idea for tube amp users to get familiar with the tech side of things, just like people do with their cars.

First, buy yourself a bias tool (mA version) and a volt/ohm meter.

Pull the chassis out, plug it into a speaker, and check to see if there's a little plastic bias pot somewhere near the tube sockets.

With the bias tool plugged between a socket and tube, with the other end plugged into the amp meter, turn the amp on, running as normal for a few minutes.

Using only one hand, preferably gloved hand, and plastic covered mini screwdriver, turn the pot slightly till 6L6's read around 30 - 32mA, and EL-34's should read around 35 - 36mA.

Keep in mind, I'm giving you the basic layman version of biasing a tube amp. This will put your amp in the perfect operating range for your tubes. A more experienced tech may do some math calculations, use an oscilloscope, and even change some resistors to dial in an amp that's not been serviced in some time.

And if you electrocute yourself, that's on you! :9: Don't ever touch anything in a live amp, especially tube pins or the bottoms of large capacitor cannisters.

Simple cheap mA bias tool.

These 6L6's are right where I suggested....30 - 32mA.

 

[ehdwuld]

Re: HOW TO BIAS getting first tube amp!! Marshall DSL 40 EL34'S

Don't do it man
It'll kill ya

Your tubes will last about 10 years or so if you do nothing. When you change tubes , let the tech check it.

There's nothing in there worth risking your life for

I am a an industrial electrician by trade
I am really comfy doing this myself. If you get comfortable one time.
Miss one thing
Pow
Lights out

Don't mess with it

Play it
When it breaks take it to a professional
Just like your car

*(Sent from my durned phone!)*

 

[Little Pigbacon]

Re: HOW TO BIAS getting first tube amp!! Marshall DSL 40 EL34'S

You can always buy another amp.
Your amp can't buy another you.

 

[tman]

Re: HOW TO BIAS getting first tube amp!! Marshall DSL 40 EL34'S

I need to know how to do this Im not finding any techs around my area that will do it so I have no choice and I want to learn.

 

[tman]

Re: HOW TO BIAS getting first tube amp!! Marshall DSL 40 EL34'S

The Marshall tech told me that the EL 34's in this model should be around 27-35 mV on each side.

 

[zzmoore]

Re: HOW TO BIAS getting first tube amp!! Marshall DSL 40 EL34'S

Send me a PM.....

 

[Boogie Bill]

Re: HOW TO BIAS getting first tube amp!! Marshall DSL 40 EL34'S

There are real dangers in tube amps; do not take these warnings lightly.

There are several companies that offer bias probes and related gear, like tedweber.com. No doubt they will have tutorials. There are several books on servicing tube amps. Aspen Pittman's book is a must have.

And honestly, one of the things I love about my Mesa amps...I don't have to re-bias the amp every time I change tubes. Saves me a lot of time...and money.

Bill

 

[Demanic]

Re: HOW TO BIAS getting first tube amp!! Marshall DSL 40 EL34'S

JJ's has a bias probe that fits between the tube and socket and reads out both in ma's and mv's and requires no extra bridging of contacts. As long as you don't touch anything other than the bias pot, you should be OK. However, if you touch the wrong thing before you've drained the residual current, you could have a problem. 500 VDC will really part your hair to say the least. Maybe the skull under it too.

Sent from my MotoE2(4G-LTE) using Tapatalk

 

[ehdwuld]

Re: HOW TO BIAS getting first tube amp!! Marshall DSL 40 EL34'S

seriously

if you are asking on an internet forum
how to bias you first real tube amp

you don't need to be poking anything in there

 

[Gearjoneser]

Re: HOW TO BIAS getting first tube amp!! Marshall DSL 40 EL34'S

I've had myself electrocuted about 4 times, and it's pretty scary to have that current vibrating through your body for a second. Luckily, I was able to pull away every time, not locked onto the chassis with both hands to my demise. That was a reminder to always approach an amp with one hand. Don't use your other hand to hold onto the chassis.

 

[Demanic]

Re: HOW TO BIAS getting first tube amp!! Marshall DSL 40 EL34'S

I've had myself electrocuted about 4 times, and it's pretty scary to have that current vibrating through your body for a second. Luckily, I was able to pull away every time, not locked onto the chassis with both hands to my demise. That was a reminder to always approach an amp with one hand. Don't use your other hand to hold onto the chassis.

An old electrician once taught me to approach a questionable circuit with one hand in my pocket, so as not to present a ground loop through the chest. Not that making ground through arm and leg was pleasant, just slightly less liable to be fatal.

I would amend your statement to say that it is pretty scary to enjoy the sensation of current vibrating through your body for a second. I'm one of those kids who enjoyed licking 9v batteries and holding on to horse coral wires for the longest. Is that TMI?

 

[zzmoore]

Re: HOW TO BIAS getting first tube amp!! Marshall DSL 40 EL34'S

I've had myself electrocuted about 4 times, and it's pretty scary to have that current vibrating through your body for a second. Luckily, I was able to pull away every time, not locked onto the chassis with both hands to my demise. That was a reminder to always approach an amp with one hand. Don't use your other hand to hold onto the chassis.

You can only be electrocuted one time.

 

[beaubrummels]

Re: HOW TO BIAS getting first tube amp!! Marshall DSL 40 EL34'S

Hmm tman hasn't posted in a while...

 

[Edgecrusher]

Re: HOW TO BIAS getting first tube amp!! Marshall DSL 40 EL34'S

I need to know how to do this

You just got the amp...so no not really. If you play out every weekend at high volumes you should get atleast a year out of the power tubes... If you play for a few hours a week in your house at lower volumes they might last 4 or 5.

If you really want to know you got time to do a little reading and gain a little background in electronics. I know tons of cats around forums who can bias an amp but really dont udnerstand it. They just go through the motions of it. Having a touch of understanding about what goes on under the hood is a huge help. If i was you I would start with an RCA Tube Recieving manual and The tube amp book by Aspen Pittmann. Those 2 things will get you started and give you some back ground so you know more than just "connect clip here... turn dial to xxxx... turn pot until y reading is reached"

but for the love of all that is guitar... just enjoy the amp... yo uhave time to learn the rest later.

 

[the toad]

Re: HOW TO BIAS getting first tube amp!! Marshall DSL 40 EL34'S

I'm curious how many people have been electrocuted by amplifiers...

Any verifiable stats/stories?

 

[PFDarkside]

Re: HOW TO BIAS getting first tube amp!! Marshall DSL 40 EL34'S

It can't be that many. How about when every TV, Radio and Record Player used tubes? Heck, clock radios had tubes! Now they are in the hands of few, they used to be in the hands of most. I think it's a carryover from that era, don't root inside a tube device, take it to a pro.

Discharging filter caps is not difficult, but it is easy to accidentally make a mistake if you don't know what you are doing.

OP, in all likelihood you don't need a rebias. Just keep playing until you need new tubes, then take it to a tech. Even if you have to book an appointment in Philly or Pittsburgh, hang out for the day and pick it up, it'll be worth it.

 

[tman]

Re: HOW TO BIAS getting first tube amp!! Marshall DSL 40 EL34'S

ok yeah Ive been studying some vids on the subject and understand what not to touch.I did see they have trim pots in these amps that you turn with screw driver to get the current you need. And I am ordering a meter and bias tool. Im not saying I needed to do it right away Im just saying that if I do happen to have a problem with a power tube or want to change brands etc.. down the road I would like to learn how to do these things myself thats all. I am aware that amps store current even if not on in the capacitors etc...And I did hear that go in with one hand safety advice. I will study more and take my time and only do it if the problem occurs.thanks for all the concern I really do appreciate it thanks

 

[Kamanda~SD]

Re: HOW TO BIAS getting first tube amp!! Marshall DSL 40 EL34'S

You're not really listening. If this is your first tube amp, don't touch the inside. Period, end of story. I've owned tube gear for 10+ years and I'll do a tube swap, but everything else goes to a tech....and I build lots of electronics!

If its a brand new amp you won't have to worry about bias anyways, play it as is, go from there. And find yourself a tech, your in PA for ****s sake, not that hard. I only have my biases checked every 3-4 tube swaps.

 

[zzmoore]

Re: HOW TO BIAS getting first tube amp!! Marshall DSL 40 EL34'S

Man.....some of you guys.......
He WANTS to learn how to bias an amp.
It's New.?
One of the power tubes Could Easily crap out tomorrow.
He may want to try different tubes, or he may (good on him) just Want To Learn.
EVERYBODY has to start.
There is absolutely no reason a competent beginner cannot be taught to bias an amp.
The number of stars that would have to align for somebody To Die from working on an amp is large.
Yes, he CAN injure himself, and he knows it. He is obviously proceeding with caution, and that is encouraging.
This is not the SDF of old I guess.