Marshall tsl 2000 bias adjusting

Guitar Tricks Forum > Tech Talk > Marshall tsl 2000 bias adjusting

New Member

Joined: 08/07/02

Posts: 7

I had found and have now lost the DIY link for a tube change / re-bias. If someone is aware of where this information is available I would appreciate it if you would post the link, thanks.

#1

I had found and have now lost the DIY link for a tube change / re-bias. If someone is aware of where this information is available I would appreciate it if you would post the link, thanks.

Big as Elvis, Baby

Joined: 11/29/01

Posts: 899

What exactly are you looking for, a how-to, or bias info? Do you usally do your own biasing? if so , what method do you use?

#2

What exactly are you looking for, a how-to, or bias info? Do you usally do your own biasing? if so , what method do you use?

New Member

Joined: 08/07/02

Posts: 7

The TSL has 'leads' in the back that you can connect a meter to and adjust accordingly. The post I saw from some forum somewhere that I lost (thinking I'd easily find it again) had specific step by step instructions as well as the proper settings. I've never done it myself before but I'm pretty handy and have read up on all the danger/methods etc. (things I should have known a long time ago, I guess I've been lucky so far in the tinkering I've done with other amps) Since this amp provides a simple avenue I am planning to do this myself once my new tubes arrive-

#3

The TSL has 'leads' in the back that you can connect a meter to and adjust accordingly. The post I saw from some forum somewhere that I lost (thinking I'd easily find it again) had specific step by step instructions as well as the proper settings. I've never done it myself before but I'm pretty handy and have read up on all the danger/methods etc. (things I should have known a long time ago, I guess I've been lucky so far in the tinkering I've done with other amps) Since this amp provides a simple avenue I am planning to do this myself once my new tubes arrive-

New Member

Joined: 08/07/02

Posts: 7

found it!

http://pub31.ezboard.com/fmarshallampsforumfrm1.showMessage?topicID=442.topic

In case others would like to know.



------------------------------------------------
I put tesla tubes in my DSL401. They are not as clean as the Ei's but sure do sound better in my opinion. As for biasing, any tech could do it. Note you only need to bias if you are replacing the output tubes. I actually biased my amp by myself. It is super easy, but you have to be extremely careful so you don't accidentally kill yourself by touching any high voltage connections. DON'T DO THIS IF YOU DO NOT KNOW HOW TO WORK SAFELY WITH HIGH VOLTAGE ELECTRONICS. Dana123 and SGstrat gave the sequence a while back and it goes something like this.

Instructions:

1) unplug the amp and remove the head unit from the cabinet.
2) locate the 3 pin molex connector labelled (CON 5).
3) securely attach the red probe of the voltmeter to one of the outer pins (use aligator clips).
4) securely attach the black probe of the voltmeter to the center pin (again use aligator clips).
5) plug the amp in (make sure the head is connected to the speaker) and let it warm up for a couple of minutes.
6) then turn on the standby and let the circuit stabilize for a few minutes.
7) adjust the mini pot (PR1) until the voltmeter reads

DSL201 0.675 V
DSL401 1.375 V
DSL50 45 mV
DSL100 90 mV
TSL60 80 mV
TSL100/122 90 mv

I bought some nonconducting pot screwdrivers
from Radio Shack for this.
turn off the amp, unplug the amp, and place the head unit back.

(optional)

9) plug in your guitar.
10) turn the amp on channel 3 making sure all knobs and the master volume are cranked.
11) play til you wake the dead.

---------------------------------------------------
service bulletin given by Dana123
---------------------------------------------------
If the tubes you replaced are exactly the same as your previous set then the bias may be close enough. That being said it is always best to check. I don't like to encourage people to bias their own amps unless they are confident in what they are doing. Below you will find the exact technical bulletin for your amp. Again please be careful. Also they recomend using a multi meter to read from the pin out biasing section of your amp. Good luck.

Dana.



MARSHALL SERVICE BULLETIN

SUBJECT: Bias Info/Procedure for JCM2000 series Marshall amplifiers

THEORY OF OPERATION: We are setting the bias using the current method instead of cross over distortion method. The Bias PCB assembly is as follows:
PR1: Bias mini-pot adjustment for pin1 which is one side of the push pull amp (two output tubes in a 100watt amp and one output tube in a
50watt amp). Pin1: Connected to the cathode of the output tube(s) which then goes through a 1 ohm resistor then to ground. Pin2: ground reference.
Pin3: Same as pin1 but for the other side of the push/pull amp. PR2: Bias mini-pot adjustment for pin3, the other side of the push/pull amp.


PROCEDURE:
1. Make sure amplifier is connected to a load with the proper impedance
selected. 2. Power up amplifier on STANDBY and let the circuit stabilize for a couple of minutes.
3. Locate the male three pin molex connector (CON2) with the two mini-pots (PR1 and PR2) on both ends found on the bottom of the tube bay. 4. Connect DMM (set to read mV) with alligator leads, reference common lead to center pin (pin2) on molex connector CON2 and positive lead to pin1 on CON2.
5. Take amplifier off of STANDBY with no signal, adjust mini-pot (PR1) closest to pin that the positive lead from your DMM is connected to and set it to the mV voltage that is listed in the chart below. 6. Repeat steps 4 & 5 for pin3 and until both pin1 and pin3 mV are the same.

BIAS CHART mV SETTINGS
(pin1 and pin3)

DSL50 45mV TSL60/1/2 80mV
DSL100 90mV DSL401 1.375V
TSL100/122 90mV DSL201 .675V

#4

found it!

http://pub31.ezboard.com/fmarshallampsforumfrm1.showMessage?topicID=442.topic

In case others would like to know.



------------------------------------------------
I put tesla tubes in my DSL401. They are not as clean as the Ei's but sure do sound better in my opinion. As for biasing, any tech could do it. Note you only need to bias if you are replacing the output tubes. I actually biased my amp by myself. It is super easy, but you have to be extremely careful so you don't accidentally kill yourself by touching any high voltage connections. DON'T DO THIS IF YOU DO NOT KNOW HOW TO WORK SAFELY WITH HIGH VOLTAGE ELECTRONICS. Dana123 and SGstrat gave the sequence a while back and it goes something like this.

Instructions:

1) unplug the amp and remove the head unit from the cabinet.
2) locate the 3 pin molex connector labelled (CON 5).
3) securely attach the red probe of the voltmeter to one of the outer pins (use aligator clips).
4) securely attach the black probe of the voltmeter to the center pin (again use aligator clips).
5) plug the amp in (make sure the head is connected to the speaker) and let it warm up for a couple of minutes.
6) then turn on the standby and let the circuit stabilize for a few minutes.
7) adjust the mini pot (PR1) until the voltmeter reads

DSL201 0.675 V
DSL401 1.375 V
DSL50 45 mV
DSL100 90 mV
TSL60 80 mV
TSL100/122 90 mv

I bought some nonconducting pot screwdrivers
from Radio Shack for this.
turn off the amp, unplug the amp, and place the head unit back.

(optional)

9) plug in your guitar.
10) turn the amp on channel 3 making sure all knobs and the master volume are cranked.
11) play til you wake the dead.

---------------------------------------------------
service bulletin given by Dana123
---------------------------------------------------
If the tubes you replaced are exactly the same as your previous set then the bias may be close enough. That being said it is always best to check. I don't like to encourage people to bias their own amps unless they are confident in what they are doing. Below you will find the exact technical bulletin for your amp. Again please be careful. Also they recomend using a multi meter to read from the pin out biasing section of your amp. Good luck.

Dana.



MARSHALL SERVICE BULLETIN

SUBJECT: Bias Info/Procedure for JCM2000 series Marshall amplifiers

THEORY OF OPERATION: We are setting the bias using the current method instead of cross over distortion method. The Bias PCB assembly is as follows:
PR1: Bias mini-pot adjustment for pin1 which is one side of the push pull amp (two output tubes in a 100watt amp and one output tube in a
50watt amp). Pin1: Connected to the cathode of the output tube(s) which then goes through a 1 ohm resistor then to ground. Pin2: ground reference.
Pin3: Same as pin1 but for the other side of the push/pull amp. PR2: Bias mini-pot adjustment for pin3, the other side of the push/pull amp.


PROCEDURE:
1. Make sure amplifier is connected to a load with the proper impedance
selected. 2. Power up amplifier on STANDBY and let the circuit stabilize for a couple of minutes.
3. Locate the male three pin molex connector (CON2) with the two mini-pots (PR1 and PR2) on both ends found on the bottom of the tube bay. 4. Connect DMM (set to read mV) with alligator leads, reference common lead to center pin (pin2) on molex connector CON2 and positive lead to pin1 on CON2.
5. Take amplifier off of STANDBY with no signal, adjust mini-pot (PR1) closest to pin that the positive lead from your DMM is connected to and set it to the mV voltage that is listed in the chart below. 6. Repeat steps 4 & 5 for pin3 and until both pin1 and pin3 mV are the same.

BIAS CHART mV SETTINGS
(pin1 and pin3)

DSL50 45mV TSL60/1/2 80mV
DSL100 90mV DSL401 1.375V
TSL100/122 90mV DSL201 .675V

Big as Elvis, Baby

Joined: 11/29/01

Posts: 899

Hey Ceej, I saw your post on the weberforum too, I agree with Lordathestrings, these are some strange numbers, I was figuring a EL34 at somewhere around 500v on the plates at 28.5 ma , Marshall must be using something different than the 1 ohm resistor method, I have heard that on some Marshalls that even the tranformer shunt method doesn't give an accurate reading, Strange, always something new to learn, Well if the amp sounds good and the tubes aren't glowing red it must be in the right ballpark and thanks for the Link.................

#6

Hey Ceej, I saw your post on the weberforum too, I agree with Lordathestrings, these are some strange numbers, I was figuring a EL34 at somewhere around 500v on the plates at 28.5 ma , Marshall must be using something different than the 1 ohm resistor method, I have heard that on some Marshalls that even the tranformer shunt method doesn't give an accurate reading, Strange, always something new to learn, Well if the amp sounds good and the tubes aren't glowing red it must be in the right ballpark and thanks for the Link.................

Big as Elvis, Baby

Joined: 11/29/01

Posts: 899

The Return of the Yammering Moron

Gee a light bulb just came on above my head, the factory settings Ceej posted are the total for all tubes in the amp, not one tube or one pair but (TSL100) 4 tubes, 4-EL34's at 90mv cathode& 1 ohm resistor method, = 22.5 ma plate current per tube, a typically conservative factory setting that makes for long tube life, I'm a Dufuss, I'm a Dufuss, I'm a Dufuss.................................

#7

The Return of the Yammering Moron

Gee a light bulb just came on above my head, the factory settings Ceej posted are the total for all tubes in the amp, not one tube or one pair but (TSL100) 4 tubes, 4-EL34's at 90mv cathode& 1 ohm resistor method, = 22.5 ma plate current per tube, a typically conservative factory setting that makes for long tube life, I'm a Dufuss, I'm a Dufuss, I'm a Dufuss.................................

Gear Guru

Joined: 01/18/01

Posts: 6242

no, you're not! no, you're not! no, you're not!

Take another look at the first paragraph of my post. I have no idea what the DSL401 has in its output stage, but to cause a 1.375 Volt drop across a 1 Ohm resistor, 1.375 AMPS are flowing. Even at the heavy Plate Dissipation my 7027A's endure at 35 ma, it would take 40 of 'em to draw that much current! :eek:

(Edit:)...and furthermore... The service bulletin says that there is one 1 Ohm resistor for each side of the push-pull output stage. So each side[/u] would be drawing 90 ma in your example, or 45 ma through each tube!

[Edited by Lordathestrings on 08-09-2002 at 10:54 PM]
Lordathestrings
Guitar Tricks Moderator

http://www.GuitarTricks.com - Home of Online Guitar Lessons

#8

no, you're not! no, you're not! no, you're not!

Take another look at the first paragraph of my post. I have no idea what the DSL401 has in its output stage, but to cause a 1.375 Volt drop across a 1 Ohm resistor, 1.375 AMPS are flowing. Even at the heavy Plate Dissipation my 7027A's endure at 35 ma, it would take 40 of 'em to draw that much current! :eek:

(Edit:)...and furthermore... The service bulletin says that there is one 1 Ohm resistor for each side of the push-pull output stage. So each side[/u] would be drawing 90 ma in your example, or 45 ma through each tube!

[Edited by Lordathestrings on 08-09-2002 at 10:54 PM]
Lordathestrings
Guitar Tricks Moderator

http://www.GuitarTricks.com - Home of Online Guitar Lessons

Big as Elvis, Baby

Joined: 11/29/01

Posts: 899

After I posted that last post, and got off the net I had one of those "Hey wait a minute, that doesn't work" moments, the 1.375v drop, just doesn't work out to anything easily calculated and the 90mv for the TSL 100 was per side, 45ma on a EL34 is not going to last to long with 500-600v on the plate, I'd like to get my hands on a TSL100, then maybe this would make some sense......

#9

After I posted that last post, and got off the net I had one of those "Hey wait a minute, that doesn't work" moments, the 1.375v drop, just doesn't work out to anything easily calculated and the 90mv for the TSL 100 was per side, 45ma on a EL34 is not going to last to long with 500-600v on the plate, I'd like to get my hands on a TSL100, then maybe this would make some sense......

Gear Guru

Joined: 01/18/01

Posts: 6242

...picture this...

pstring in a music shop, talking to salesman: "I don't want to buy the damn thing, I just want to pull it apart!... :D
Lordathestrings
Guitar Tricks Moderator

http://www.GuitarTricks.com - Home of Online Guitar Lessons

#10

...picture this...

pstring in a music shop, talking to salesman: "I don't want to buy the damn thing, I just want to pull it apart!... :D
Lordathestrings
Guitar Tricks Moderator

http://www.GuitarTricks.com - Home of Online Guitar Lessons