Lonestar bias mod

[splatter]

I'm new to this forum so if this has been covered before please forgive my ignorance .
I recently purchased a lonestar after seeing the Andy Timmons video on you tube .After getting it home and spending some time with it my impressions were that channel 1 sounded dry and lifeless ,had no sparkle to it at all . Channel 2 had a good lead tone but was a bit fizzy and like all mesa amps the bottom end was muddy and farted out . So since I bought my amp used and had nothing to lose in the warrenty department I decided to mod the amp . I pulled the load resistor and replaced it with a bias pot that I purchased from mansfield guitars . Thay sell A "bias mod kit" which consist of a pot and a resistor soldered to a small pcb. then I biased the amp up to 65% and man what a difference . Channel 1 now has the sparkle and chime I have only found in fenders . Channel 2 no longer has the fizz I spoke of and the muddy farty bass is a thing of the past . Mesa says their amps are fixed bias for maintenance free preformance and I guess to some degree this is true . However some would argue that its to sell mesa tubes . My lonestar was biased at 30% which kills the amps ability to preform the way I want it to . As I said earlier I brought the amp up to 65% which is where I found what I considered to be the best tone .Is there a down side ? Yes there is your tubes won't last as long as before but to me its a trade off that is well worth it .
For the last few years I have been playing boutique amps and I am somewhat of a tone snob . Since doing the mod on the lonestar I hardly play my boutique amp at all ,yes the mesa sounds that good .

 

[plan-x]

Always love a mod thread. Thanks for sharing. Get ready for the questions to come like which Lonestar, the LSC(100w) or LSS(30w)? How did you determine the bias percentage from 30% to 65%?

 

[djw]

Yes, very interesting. Always good to get a new tinkerer in here.

Splatter, I guess my initial question is: is this mod any different from compensating with tubes that run hotter in the LS than the Mesa tubes do? Doesn't this do basically the same thing, except with a variable control (which is very cool)?

 

[splatter]

Always love a mod thread. Thanks for sharing. Get ready for the questions to come like which Lonestar, the LSC(100w) or LSS(30w)? How did you determine the bias percentage from 30% to 65%?

it is a lsc 50/100w model . The bias % is determined with this formula (tube wattage / plate voltage x % ) for example a 6l6 tube is generally considered to be 30 watts the plate voltage on my lonestar was about 475v if i remember correctly so 30/475 = .63ma x.65=41ma so to bias it at 65% i set the bias for 41ma . to determine what it was already set at I just took the bias reading and did the math in reverse .
Btw some people like the bias set a little lower some like it set a little higher . The best way to do it is have your guitar plugged in while you set the bias and adjust it to what you like best . However don't do it without a meter connected a rule of thumb for class a/b amps is 70% or less .To my ears on most amps 65% is generally the sweet spot .

 

[splatter]

Yes, very interesting. Always good to get a new tinkerer in here.

Splatter, I guess my initial question is: is this mod any different from compensating with tubes that run hotter in the LS than the Mesa tubes do? Doesn't this do basically the same thing, except with a variable control (which is very cool)?

it does the same thing as running hotter tubes . the difference is that with this you have the ability to really tweek it to your liking . I'm not a tube expert so I don't know for sure but I doub't if you can find a tube that will run twice as hot as another . in other words I doubt you could find a tube that would bring the bias on your amp from say 30% up to 60 or 70 %. so while you may see some improvement I don't think you could accomplish the same level of change that you can with this mod .
BTW for someone with a little knowledge of electronics and good soldering skills this is really easy to do . You will however need a bias probe and a dvm.

 

[Charles Reeder]

Congrats on doing the bias mod!

For us ignorant stiffs out there...do you think you could post some pictures of the inside of the amp with the mod...showing the parts you installed....plus a picture of the load resistor you removed?
If you did that and supplied us with the exact catalog number of the kit you used (and supplier's address) I think you will find that a bunch of folks might be interested in pursuing this.
It's so...so true that when you buy any Mesa...the tubes in it will all be 'safe' to use, but not necessarily toneful. I bought 2 Lonestars and the tubes in them varied from about 22mv in one amp to about 28mv in another amp! Both too cold. By experimentation I have several sets of 6L6's that meet my tone needs. I have sets which read 35-38mv and sets which read 41-43mv. I place a pair of the 'hotter' (41-43mv)tubes in the outer sockets for use at 50-watts, and get good warm saturation and sparkle. I put a pair of the 'warm' (35-38mv) tubes in the inner sockets. This extends my clean headroom when I use the amp at the 100-watt setting.

Doing the bias mod would eliminate the need to select special 'graded' tubes (Mesa or other brands) and allow any tubes to be biased to the desired percentage at will.
This of course brings up another possible mod...having the outer pair of tubes and the inner pair of tubes...independantly adjustable, so that you can set the outer tubes hotter than the inner tubes.

I have been doing this with tubes...both 6L6's, 6V6's, and EL-34's for the past several years...but having adjustable bias would make things so much more controllable.

In fairness to Mesa and their position on fixed bias...you CAN buy Mesa tubes which will bias up to 44-48mv in the Lonestar...you just have to specifically ask for them! Some people do like the cooler (cold to me) sounding tubes...and if you like the sound of the tubes in your amp (whether cold, cool, warm or hot) re-ordering the same color code will get you another set that matches! By maintaing their fixed bias policy...they can guarantee that they can get you into any performance area that you desire (from cold to hot and anywhere in between). They weed out the tubes at either extreme of the equation which would either not function or go way over the top with super hot biasing. So, any color-code you order from them will be safe in your amp...but the results will vary according to the color-code. Call and ask them...since both my Lonestars respond identically to the various color-codings...I think it's safe to assume most all of them will. The same being true for my Stiletto. Give them a call and tell them what you want!
Anyway...I look forward to seeing those pictures of the mod, if you get the chance.

Cheers, Charles

 

[splatter]

Congrats on doing the bias mod!

For us ignorant stiffs out there...do you think you could post some pictures of the inside of the amp with the mod...showing the parts you installed....plus a picture of the load resistor you removed?
If you did that and supplied us with the exact catalog number of the kit you used (and supplier's address) I think you will find that a bunch of folks might be interested in pursuing this.
It's so...so true that when you buy any Mesa...the tubes in it will all be 'safe' to use, but not necessarily toneful. I bought 2 Lonestars and the tubes in them varied from about 22mv in one amp to about 28mv in another amp! Both too cold. By experimentation I have several sets of 6L6's that meet my tone needs. I have sets which read 35-38mv and sets which read 41-43mv. I place a pair of the 'hotter' (41-43mv)tubes in the outer sockets for use at 50-watts, and get good warm saturation and sparkle. I put a pair of the 'warm' (35-38mv) tubes in the inner sockets. This extends my clean headroom when I use the amp at the 100-watt setting.

Doing the bias mod would eliminate the need to select special 'graded' tubes (Mesa or other brands) and allow any tubes to be biased to the desired percentage at will.
This of course brings up another possible mod...having the outer pair of tubes and the inner pair of tubes...independantly adjustable, so that you can set the outer tubes hotter than the inner tubes.

I have been doing this with tubes...both 6L6's, 6V6's, and EL-34's for the past several years...but having adjustable bias would make things so much more controllable.

In fairness to Mesa and their position on fixed bias...you CAN buy Mesa tubes which will bias up to 44-48mv in the Lonestar...you just have to specifically ask for them! Some people do like the cooler (cold to me) sounding tubes...and if you like the sound of the tubes in your amp (whether cold, cool, warm or hot) re-ordering the same color code will get you another set that matches! By maintaing their fixed bias policy...they can guarantee that they can get you into any performance area that you desire (from cold to hot and anywhere in between). They weed out the tubes at either extreme of the equation which would either not function or go way over the top with super hot biasing. So, any color-code you order from them will be safe in your amp...but the results will vary according to the color-code. Call and ask them...since both my Lonestars respond identically to the various color-codings...I think it's safe to assume most all of them will. The same being true for my Stiletto. Give them a call and tell them what you want!
Anyway...I look forward to seeing those pictures of the mod, if you get the chance.

Cheers, Charles

thanks for the info Charles . I had no Idea that mesa offered different tubes like that .
here are some pics of the amp after the mod .

as you can see from the photos I opted to mount the bias pot on the outside so that when I change tubes I won't have to open the amp up . If you don't like the way it looks you can always mount it on the inside .\

Here is a link to ebay where you can find the pot .http://cgi.ebay.com/Bias-Mod-Mesa-Boogie-Marshall-Fender-Peavey-Vox-/320510207372?cmd=ViewItem&pt=LH_DefaultDomain_0&hash=item4a9fe5a58c
This is where I got mine. It comes with a schematic with the load resister circled . You can also send your amp to them and have them preform the mod . but then theres shipping and bench fees . If you don't feel comfortable preforming the mod then order the part and have a local tech do it . Remember there are VERY HIGH VOLTAGES PRESENT EVEN WITH THE AMP OFF AND UNPLUGGED .
I hope this helps ,this mod made all the difference between me keeping and selling the amp.

 

[plan-x]

So...you took out the 22k resistor and soldered in the red wires from the bias pcb? How do I measure plate voltage? Sounds dangerous :shock: 470v, Forget that, I'll use your numbers.

The best way to do it is have your guitar plugged in while you set the bias and adjust it to what you like best . However don't do it without a meter connected a rule of thumb for class a/b amps is 70% or less .

Can the bias be set by braile so to speak. I do have an analog meter (wally-mart) which only goes to 250v on the needle.

Edit: Ok, I guess that bias probe they sell is what I would need.

 

[handyandy]

Very interesting!
Thanks for sharing this mod, Will the components used work with UK amps with higher voltage?
Also what about the v.2 with the 10watt/class A switch, will running at 60-70% have the same effect on class A operation?
Great mod!!!

 

[splatter]

So...you took out the 22k resistor and soldered in the red wires from the bias pcb? How do I measure plate voltage? Sounds dangerous :shock: 470v, Forget that, I'll use your numbers.

The best way to do it is have your guitar plugged in while you set the bias and adjust it to what you like best . However don't do it without a meter connected a rule of thumb for class a/b amps is 70% or less .

Can the bias be set by braile so to speak. I do have an analog meter (wally-mart) which only goes to 250v on the needle.

Edit: Ok, I guess that bias probe they sell is what I would need.

Yes I took the resister out and put the pot in its place .
I belive its pin 3 on the tube that gives you the plate voltage .I really don't remember . I usually just hit the pins with the volt meter till I see the voltage I'm looking for . YOur gonna have the amp open and on any way so you might as well get your own plate voltage . I really don't remember exactly what mine was . I think I wrote it down so i'll see if I can find it .

NOTE :iF YOU HAVE NEVER BIASED AN AMP YOU NEED TO RESEARCH IT BEFORE ATTEMPTING IT . THERE ARE DETAILED INSTRUCTIONS THAT CAN BE FOUND ON THE INTERNET . ALSO ALWAYS BIAS WITH A LOAD ON THE SPEAKER OUTPUT

you really need a dvm capable of measuring mv . If you bias by ear alone you run the risk of frying your tubes .webber sells a bias probe called the bias rite . I think it has functions to read plate voltage as well as the biased voltage . I hear its really pricey though . I use a 2 tube bias probe I got off fee bay for about $30 and a dvm .

 

[splatter]

Very interesting!
Thanks for sharing this mod, Will the components used work with UK amps with higher voltage?
Also what about the v.2 with the 10watt/class A switch, will running at 60-70% have the same effect on class A operation?
Great mod!!!

I really don't know . You can contact mansfield guitars ( the people that sell the mod ) and I'm sure they could tell you .
I would imagine it will work fine for class A however in class A I think the bias is usually set higher . I'm sure mesa incorporates this in their design so I would think it would be fine on the newer models with the 10 w setting. Again I'm sure mansfield guitars could answer this for you .

 

[Charles Reeder]

Bravo Splatter!
You have done every Lonestar 'lover' a great service! I expect we'll have a slew of daring souls going 'one-step-further' in the pursuit to take full control of their Lonestar sound.

I WILL be doing this bias mod...although I can't say when for sure as I am very busy now and one amp travels with me...the other is at a club. So, don't expect to hear my personal comments anytime soon....but they will be forthcoming in time.

The decision to mount the bias control on the exterior of the amp is one which I concur with...just be careful not to bump it or spill anything on it. I think I might drill a small hole through the chassis to run the wires through....and mount the pcb board inside a small box mounted on the underside of the chassis...with just the screw adjustment accessable. Just my thought on the subject.

Thanks again for the great pictures and valuable information!

Cheers, Charles

 

[splatter]

Bravo Splatter!
You have done every Lonestar 'lover' a great service! I expect we'll have a slew of daring souls going 'one-step-further' in the pursuit to take full control of their Lonestar sound.

I WILL be doing this bias mod...although I can't say when for sure as I am very busy now and one amp travels with me...the other is at a club. So, don't expect to hear my personal comments anytime soon....but they will be forthcoming in time.

The decision to mount the bias control on the exterior of the amp is one which I concur with...just be careful not to bump it or spill anything on it. I think I might drill a small hole through the chassis to run the wires through....and mount the pcb board inside a small box mounted on the underside of the chassis...with just the screw adjustment accessable. Just my thought on the subject.

Thanks again for the great pictures and valuable information!



Cheers, Charles

Thanks Charles and if you look closely you can see i mounted the bias pot on the under side of the chassis where it is protected . 8)

 

[fishyfishfish]

Wow, if that came out when I had my amp, I probably would of kept it.

 

[pine]

So does 1 bias pot run all 4 power tubes, or do you need a bias pot for each pair?

 

[Charles Reeder]

Hey Pine:
The bias mod featured here...just uses one potentometer which adjusts all 4 output tubes. Most bias adjustments work that way and it is adequate for most folk's needs.

Some bias mods allow individual adjustment of the inner and outer pairs of output tubes in amps having 4 output tubes.

I wouldn't hesitate at all to do the mod with the single bias adjustment. Personally, I DO like to run my outer pair of output tubes a bit hotter than my inner pair. But, that can be done quite easily by using two pairs of tubes with differing 'hardness'.

Cheers, Charles

 

[splatter]

So does 1 bias pot run all 4 power tubes, or do you need a bias pot for each pair?

Charles is correct 1 pot for all 4 tubes .

 

[handyandy]

OK, Ive been told that most mesa amps with power switching switch in a cathode resistor to control bias in low wattage modes but still use fixed bias in high wattage modes. If that is the case then bias will not be adjustable in 10 watt mode but fully adjustable in 50&100 watt mode.
I just recieved my mod kit today but I dont have the tools for measuring plate voltages etc. Nor do I have the experience!
I think my best option now is to get a tec to do it for me and give me the plate voltage and safe operating limits for biasing so I can bias myself in the future.
Thanks again splatter for this mod!!

 

[splatter]

OK, Ive been told that most mesa amps with power switching switch in a cathode resistor to control bias in low wattage modes but still use fixed bias in high wattage modes. If that is the case then bias will not be adjustable in 10 watt mode but fully adjustable in 50&100 watt mode.
I just recieved my mod kit today but I dont have the tools for measuring plate voltages etc. Nor do I have the experience!
I think my best option now is to get a tec to do it for me and give me the plate voltage and safe operating limits for biasing so I can bias myself in the future.
Thanks again splatter for this mod!!

Your welcome H.A. and yes I sent a message to mansell guitars and they told me what you just said that the mod wouldn't effect the 10w setting but would work on the 50/100 w settings . And yes it might be wise to get a tech to install it for you if your not comfortable doing it . You will need a bias probe and a DVM to bias in the future though .
BTW I did the pot swap mod on mine after doing the bias mod and it made my amp sound even better .

 

[pine]

I just did the bias mod on my out-of-warranty LSC and after an easy installation measured my plate voltage with a Weber bias rite at 466 Volts. The OEM bias setting had been set to 36 mA giving me a plate dissipation of only 16 watts. I had to turn the bias adjustment several times to get the bias up to 43 mA. As Splatter reported, the difference was striking, it was like a new , better sounding amp in both channels, and I just couldn't believe the improvement in tone. I haven't really put it through it's paces but the overall feel and tone of the amp are just amazing.

Thanks, Splatter!