Adjustable-Bias-Kit in Stiletto GREAT SOUND!

[Riff Blister]

OK, I'm two weeks into my Stiletto with the Mansfield Adjustable Bias mod. It's been great!!!
I haven't gigged with the amp but my home practice space is large and I live in a spacious neighborhood. I can at least crank up to match a good drummer's volume without having a squad car pull up my driveway.
The very first thing I noticed was the added girth in the midrange. Great on Channel 1 Crunch. Even more so on Channel 2 Tight Gain. I love that!!!
Secondly, and probably the most important to a lot of people, the harsh high end is gone!!!
Sh*# Yeah!!!!!!!
No matter how I tried (within reasonable settings) I can't dial it back in. Bringing up the Presence and Treble adds brightness of course but not the spiky bad stuff. Don't misunderstand though, it's still a Stiletto and it's inherent design to "cut" is still there.
It still sounds like a Stiletto.
An interesting side point is that I now am liking some of the different setting that I never liked so much before. I've always preferred running Bold and Silicon Diodes. Now I am finding that Spongy and tube rectifiers are sounding damn good too. It could be just me but that's what I'm liking.
Thank you John Mansfield for building this little device.
Thank you guy named Splatter and Charles Reeder for bring this information to us on the Boogie Board.
Thanks also to amp tech Casey Gooby for the professional installation.
Ah, what the hell. Thanks Mom and Dad for all you've done too.





Thank you BB readers for putting up with this long wind bag post.
Mark

[inkwachemis]

OK, I'm two weeks into my Stiletto with the Mansfield Adjustable Bias mod. It's been great!!!
I haven't gigged with the amp but my home practice space is large and I live in a spacious neighborhood. I can at least crank up to match a good drummer's volume without having a squad car pull up my driveway.
The very first thing I noticed was the added girth in the midrange. Great on Channel 1 Crunch. Even more so on Channel 2 Tight Gain. I love that!!!
Secondly, and probably the most important to a lot of people, the harsh high end is gone!!!
Sh*# Yeah!!!!!!!
No matter how I tried (within reasonable settings) I can't dial it back in. Bringing up the Presence and Treble adds brightness of course but not the spiky bad stuff. Don't misunderstand though, it's still a Stiletto and it's inherent design to "cut" is still there.
It still sounds like a Stiletto.
An interesting side point is that I now am liking some of the different setting that I never liked so much before. I've always preferred running Bold and Silicon Diodes. Now I am finding that Spongy and tube rectifiers are sounding damn good too. It could be just me but that's what I'm liking.
Thank you John Mansfield for building this little device.
Thank you guy named Splatter and Charles Reeder for bring this information to us on the Boogie Board.
Thanks also to amp tech Casey Gooby for the professional installation.
Ah, what the hell. Thanks Mom and Dad for all you've done too.





Thank you BB readers for putting up with this long wind bag post.
Mark

this is great info.

I think I'm really considering doing this to my Ace.

thing is, I bought a new set of tubes from dougstubes.com and just from that I noticed a much much better differnce in tones compared to the stock tubes. I assume he sent me a hotter power tube set, however I don't know what range these tubes put my amp bias in now. I wonder if these power tubes that I have now put my amp into the recommended 39mv range?
curiously, I looked at the box that the tubes came in and on them are marked: "Plate current (ma):38.6, 39.3" for each power tube box. what does that mean? does that mean when I put these tubes into my amp it automatically put my amp into the 39mv bias range as recommended? sorry, I don't know too much about biasing amps! more info please!
ps- the tubes are winged =C= SEDs el34s

[Charles Reeder]

inkwachemis:

About those tubes...it does sound as if the tubes were checked against the known value of the Ace's bias resistor and guaged correctly to get you in the 39 (+/-) range. But to be sure; contact your tube supplier and ask him outright.
The Ace being a 'Stage-2' Stiletto; is somewhat brighter than the 'Stage-1's'. It might benefit you to 'bump-up' the bias slightly into the 42mv range. But if it sounds good enough to suit you...leave it alone!

Charles

[inkwachemis]

inkwachemis:

About those tubes...it does sound as if the tubes were checked against the known value of the Ace's bias resistor and guaged correctly to get you in the 39 (+/-) range. But to be sure; contact your tube supplier and ask him outright.
The Ace being a 'Stage-2' Stiletto; is somewhat brighter than the 'Stage-1's'. It might benefit you to 'bump-up' the bias slightly into the 42mv range. But if it sounds good enough to suit you...leave it alone!

Charles

thanks for the info.

I guess the only way to really know is to take a meter reading on my amp, but i dont know how! Im considering picking up a Weber bias rite. will this help get me a reading on where my current amp is set to? interesting on the info that u mention about bumping up the bias to 42mv. I guess this is only possible currently if I install an adjustible bias kit yea?

[Charles Reeder]

Yeah you'll need some kind of bias tool.

It's NOT necessary to spend big bucks though. The bias unit I have is a single (it measures 1 tube at a time) and that's all you REALLY need unless you are doing this for a living.
It plugs into one of your tube sockets...you plug the output tube into it...and using a digital-multimeter you connect to the 2-leads coming off the unit. It's not only easy-but it's F-A-R SAFER than the 'old' way which involved tapping directly into the tube sockets (from inside the amp). I can't remember who I bought from...but I think they were out of Georgia...the unit was about $26.00...and came with a VERY helpful guide to the min/max settings for all the popular output tubes. My multimeter was a whopping $19.99 at Radio-Shack.
Check ebay under bias and you'll find a usable unit cheap enough.

Yeah, you'd need to install a 'bias-kit' such as Mansfield sells to 'bump' your bias up to 42mv. But, even if it turns out you are quite happy with the bias where it was...you just need to keep a record of that reading...and set ANY other tubes you get to that setting. You can now 'take-a-chance' on those expensive NOS tubes everybody brags about (if you want to indulge yourself and your amp). 'Cause it really won't matter whether thet are by nature hot or cold...you'll be able to bias them to the setting you want.

That's why I really wanted one for my Lonestar. I was able to get 'close' to what I wanted (35-39mv) with Mesa yellow 6L6's...but NEVER was able to get any RCA, GE etc NOS tubes that read above approx.19mv. Now I am free to experiment; and every tube I own is now usable.

As for my Stiletto (Deuce 1); I never found a tube that would get me up to 39mv. If Doug's has some he can supply that will meet those specs. that's great! But now I'm not dependant on any one supplier (and the cost of their 'matching' services). All my previously too cold EL-34's are now usable.

Now a few words about biasing in general. Suppliers will send you (so-called) matched pairs or quads. Usually the tubes will match each other within 3mv or less. So if you ordered a pair that were not perfectly matched...just split the difference. Measure each tube and you could set one at 37.5 and the other at 40.5mv. This would 'average' out to a 39mv bias. So, even if you buy the single unit bias tube...take the time to test all your tubes in it and allow for slight mis-matches.

Check for 'tube-drift'. After tubes burn in for a lengthy period of time they are usually stable for a long period of time (but not always). Tubes are....well tubes, and they act in accordance to their own rules. Many suppliers 'pre-burn' their tubes for X-amount of hours to stabilize them before performing the matching process...but this does not always work...and some suppliers don't do it at all.
After you've biased and used your amp for a 'gig' or lengthy practice session...check the bias again. Thereafter, check the bias whenever you're looking for something constructive to do. I've installed matched tubes only to find that one has 'drifted' 17mv since I last checked it. A Fender HotRod Deluxe...biased at 35mv per tube. When I checked back...a month or so later; one was still dead on at 35mv...the other was reading 52mv!
So you see...the aquisition of the biasing tools (and adjustable bias) will allow you to check for problems that never would otherwise be apparent until they created problems.

A 'runaway' tube can wreak havoc. I was checking a reading on an amp once and every few minutes one tube would 'creep-up' a little. I finally discarded the tube when it 'creeped-up' to 64mv after having been set with it's twin at 39mv. That tube was a disaster waiting to happen.

Don't discard the tubes that have only 'drifted' over a period of time. Hang on to them as you may end up with a mate for it one day. The 6L6 which drifted in my HRD eventually found a match.
But, if you encounter a 'run-away' tube (this is one that slowly...or maybe not-so-slowly... keeps getting hotter and hotter after the bias is set) get rid of it; so that you don't accidently use it by mistake one day.

I hope none of this 'puts you off' from getting the equiptment. It's meant to encourage you. You will be able to get the best performance from your amp as well as diagnose minor tube problems before they create major amp problems.

Charles

[Trev57]

Another great post from Charles. Really useful info. Thanks. And you can buy a single bias probe from Mansfields.

[Riff Blister]

Another great post from Charles. Really useful info. Thanks. And you can buy a single bias probe from Mansfields.

I agree. Very helpful.
Thanks again Charles.

[inkwachemis]

Yeah you'll need some kind of bias tool.

It's NOT necessary to spend big bucks though. The bias unit I have is a single (it measures 1 tube at a time) and that's all you REALLY need unless you are doing this for a living.
It plugs into one of your tube sockets...you plug the output tube into it...and using a digital-multimeter you connect to the 2-leads coming off the unit. It's not only easy-but it's F-A-R SAFER than the 'old' way which involved tapping directly into the tube sockets (from inside the amp). I can't remember who I bought from...but I think they were out of Georgia...the unit was about $26.00...and came with a VERY helpful guide to the min/max settings for all the popular output tubes. My multimeter was a whopping $19.99 at Radio-Shack.
Check ebay under bias and you'll find a usable unit cheap enough.

Yeah, you'd need to install a 'bias-kit' such as Mansfield sells to 'bump' your bias up to 42mv. But, even if it turns out you are quite happy with the bias where it was...you just need to keep a record of that reading...and set ANY other tubes you get to that setting. You can now 'take-a-chance' on those expensive NOS tubes everybody brags about (if you want to indulge yourself and your amp). 'Cause it really won't matter whether thet are by nature hot or cold...you'll be able to bias them to the setting you want.

That's why I really wanted one for my Lonestar. I was able to get 'close' to what I wanted (35-39mv) with Mesa yellow 6L6's...but NEVER was able to get any RCA, GE etc NOS tubes that read above approx.19mv. Now I am free to experiment; and every tube I own is now usable.

As for my Stiletto (Deuce 1); I never found a tube that would get me up to 39mv. If Doug's has some he can supply that will meet those specs. that's great! But now I'm not dependant on any one supplier (and the cost of their 'matching' services). All my previously too cold EL-34's are now usable.

Now a few words about biasing in general. Suppliers will send you (so-called) matched pairs or quads. Usually the tubes will match each other within 3mv or less. So if you ordered a pair that were not perfectly matched...just split the difference. Measure each tube and you could set one at 37.5 and the other at 40.5mv. This would 'average' out to a 39mv bias. So, even if you buy the single unit bias tube...take the time to test all your tubes in it and allow for slight mis-matches.

Check for 'tube-drift'. After tubes burn in for a lengthy period of time they are usually stable for a long period of time (but not always). Tubes are....well tubes, and they act in accordance to their own rules. Many suppliers 'pre-burn' their tubes for X-amount of hours to stabilize them before performing the matching process...but this does not always work...and some suppliers don't do it at all.
After you've biased and used your amp for a 'gig' or lengthy practice session...check the bias again. Thereafter, check the bias whenever you're looking for something constructive to do. I've installed matched tubes only to find that one has 'drifted' 17mv since I last checked it. A Fender HotRod Deluxe...biased at 35mv per tube. When I checked back...a month or so later; one was still dead on at 35mv...the other was reading 52mv!
So you see...the aquisition of the biasing tools (and adjustable bias) will allow you to check for problems that never would otherwise be apparent until they created problems.

A 'runaway' tube can wreak havoc. I was checking a reading on an amp once and every few minutes one tube would 'creep-up' a little. I finally discarded the tube when it 'creeped-up' to 64mv after having been set with it's twin at 39mv. That tube was a disaster waiting to happen.

Don't discard the tubes that have only 'drifted' over a period of time. Hang on to them as you may end up with a mate for it one day. The 6L6 which drifted in my HRD eventually found a match.
But, if you encounter a 'run-away' tube (this is one that slowly...or maybe not-so-slowly... keeps getting hotter and hotter after the bias is set) get rid of it; so that you don't accidently use it by mistake one day.

I hope none of this 'puts you off' from getting the equiptment. It's meant to encourage you. You will be able to get the best performance from your amp as well as diagnose minor tube problems before they create major amp problems.

Charles

WOW!

thank you so much for the wealth of info you have shared and not only in this thread but in your other posts as well.

I think I know how to go about this right now. I'm gonna first find a way to get a bias reading on my amp to get a base reading. This will give me a better idea of whether or not setting up my amp for adjustable bias may or may not make a significant difference for me. If I find that my bias is considerably lower than the target range of 39 and up to 42mv for my Ace, then I will consider trying out the bias adjustment thingie. thanks!

[alie123]

Hi Everybody,

I also have the bias kit and probe for my Stiletto ACE .. Haven't installed the kit yet, but I've installed the bias probe to measure how 'cold' my amp was with my current tubes.

Some guys also have installed the bias kit. I'd like to share some info, and want to know what you guys have experienced..

What I noticed: I'm getting different results in the different channels. Each channel has 3 modes.
This is what I measure: (after a few minutes in play mode)

(values shown in DC A)
Channel1 - mode fat clean : 0,042
Channel1 - mode tite clean : 0,041
Channel1 - mode crunch : 0,031 / 0,032 (!!!l!) --> This mode sounds incredible THIN/ICE picky. Is this because of the lower value!?
Channel2 - mode crunch: 0,031 (also low / and sounds thin)
Channel2 - mode tite gain :0,031 (also)
Channel2 - mode fluid drive : 0,031 (also)

Each channel has a tube or diode switch.
All measurements were done with the channel set in the DIODE setting.
(When I set to TUBE, all measurements in all modes in both channels are 0,018 ..)
..Is this weird?

So, what I measure is exactly what I noticed...--> The cleans sounds more warmer then the overdriven sounds.
But is 0,031 'cold' ?

What was your experience with all above info?
Is my amp biassed at 0,018 (18 miliamps) or biased at variable settings (like clean on 42 mA and drive on 31 mA.. ??!

Thanks!

[FlyingFin]

Hi Folks..
I've been reading this board for a while now and finally took the time to register.

Anyway, I have made the same discoveries as alie123 here. The anode current keeps changing as you go through the different modes the most distinctive drop being found between clean and distorted channels. The rectifier setting also makes a difference, as being stated before.

Now this got me thinking...should I sacrifice the clean tones all together to achieve the best possible crunch or bias the amp as hot as it can go on the clean settings and just live with the fact that it leaves the drive channels a bit cold?

The difference between 30mA - 40mA is very audible on the crunch channels.

[alie123]

Thanks FlyingFin, Im glad to read that you´ve also have the same problem. Otherwise my amp is maybe broke..

I read on the board the good reviews after installing te mod and biassing it. Im very curious how you guys have biassed your amp.

Like: in what mode (bold/spongy), channel(1 or 2) and rectifier choice (tube/diode).

I simply want to raise my bias on channel2 up to 36 (now 31, with power BOLD, channel2 (all modes) and diode rectifier. But I'm afraid my clean channel bias would be a bit too high, because it is already high..

Thanks!

[fbomb]

CLIPS !!!

[splatter]

I'm thinking about trying a stiletto but to me the gain is just really lose sounding in all the clips I have heard . I'm not that concerned about the cleans cause I rarely use the clean channels and I have a lonestar if I need cleans . I know what the bias mod did for the lone star and I'm wondering if the bias mod tightens up the gain on the stiletto ? your input is appreciated
Thanks
splat

[Riff Blister]

Hey splatter
Gee, I don't know, I always thought the gain was pretty tight sounding on my Deuce . Even before the mod.
It sure sounds that way next to my band mates Shiva. And my Budda for that matter.

fbomb is desperately looking for someone to post some clips of the mod.
I'd like to accommodate you sir but being a pretty low tech garage rocker I just don't have the means at the moment.
I don't think anything from my hand held Tascam will do it justice.

Maybe someone living in the 21st century can step up to the plate.

[splatter]

Hey splatter
Gee, I don't know, I always thought the gain was pretty tight sounding on my Deuce . Even before the mod.
It sure sounds that way next to my band mates Shiva. And my Budda for that matter.

fbomb is desperately looking for someone to post some clips of the mod.
I'd like to accommodate you sir but being a pretty low tech garage rocker I just don't have the means at the moment.
I don't think anything from my hand held Tascam will do it justice.

Maybe someone living in the 21st century can step up to the plate.

Ive been playing splawns for a few years and now I'm playing a Friedman KS marshall so I guess I'm kinda use to really tight gain . Don't mean to sound like a tone snob but I guess i am