Bias Mod installed. Need a bit of help.

I have installed the Bias Mod Kit from Mansfields in my Stage 1 Stiletto. I took a reading using the Bias Probe before and after using Mansfields instructions, but I am not getting anything that makes sense to me. Am I using the wrong meter setting? Any other DCA settings give me a zero reading.

The meter reads 0.4 in the 200u setting. My meter options are 200u, 2000u, 20m or 200m. DCV set on 1000 reads 456. I did adjust the resistance of the bias pot to match the resistor that was removed. I plugged the bias probe into my Marshall just to see what happens, and I get the same kind of 0.4 - 0.6 reading.

I have some pics, but this forum doesn't give me an option to post them.

Any help would be appreciated.

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Trev,

I have been helping you with this issue via email in every possible way. I understand your frustrated but everything you have done so far has been a result of user error. I personally test every meter before it gets boxed for shipping so I can guarantee that your probe left here in perfect working order. I also understand that things happen during transit and if the probe is defective I will gladly replace it. As I stated in the email, everytime you hook your meter up wrong, you run the risk of damaging your meter. Also you are using a very cheap meter which when used properly will work just fine but I wouldn't expect too much when using it wrong. You stated you are checking your probe using resistance readings. The best way to check is with a continuity tester. There is virtually nothing to go wrong on these other than a broken wire or solder joint. You also had this thing shipped around from me to Florida and then to the UK. For tracking reasons and other issues I only ship international using express international shipping. I'm sorry that it's more expensive but there are reasons why I use that method. I have had to many lost packages with priority international and I have to eat the cost everytime so I don't use that method anymore.

Based on what I have seen I would not suggest using another method since it involves altering the cathodes on the power tubes to safely do it or using the output transformer shunt method which can be very dangerous to you and your amp. Lets get the problem with the probe solved so you can bias properly and safely. For the time being make sure your trim pot is set to match the factory resistor setting and all will be good until we get this issue resolved.

Thanks
John

I will find another meter and try that. Thanks for the help John.

I think he just wants to know if hes using the meter correctly.

Trev57:

Sorry to hear about your problems...BUT, I Don't think the meter is the problem.
Here's why. As I have stated many times...I am NOT a tech...and my soldering skills etc. are limited. I have installed 2 bias kits thus far. 1 on a Lonestar and 1 on a Stiletto Deuce 'Stage 1'.

I was getting some wild readings like you are getting when I first went to set the bias on my Lonestar after installing the mod. The fault was mine! I was not getting a good connection. Where I had soldered the lead wires from the bias mod onto the Lonesatr circuit board (the 2 spots where the 22K resistor had been removed) one of the connections had a little play in it...so the circuit was cutting in and out, giving false resistance readings.

I resoldered (carefully) and my next attempt to set the bias was a success. Keep in mind that this is a tight location (even more so on the Stiletto)...so when I installed the kit in my Stiletto I used a different method to complete the circuit. The resistor which you are supposed to remove is VERY close to either another resistor or a small capacitor (I forget which now). When adding the bias-mod to the Stiletto; I didn't unsolder the resistor...I used some wire snips to cut it in half. I cleaned all the 'stuff' off of the resistor wires that were now exposed....bent these wires to my right (away from the nearby resistor?/capacitor?)...and soldered the wires from the bias mod kit onto these wires. I carefully wrapped them tightly together and crimped them before soldering. Afterwards I put a little electrical tape around the connections. (probably unnecessary).

You must be VERY careful with the soldering iron around any components in the amp or the kit...I inadvertantly loosened one of the components on the kit's little circuit board with just a moment of inattention.

But I repeat...your meter is giving the exact same type of nonsense readings I was getting from my Lonestar which was due to a loose solder joint where the kit was connected to the Lonestar's main circuit board. You also could have 2 wires which are sometimes touching and grounding each other out. Give it all a good looking over.

I hope you solve your problem soon....'cause I believe that you are really going to be delighted with the results.

Cheers: Charles

At the moment I have to assume John is right and I have screwed up the meter. The amp still works as it did before, plus I got the exact same result on my Marshall. If the mod kit wasn't soldered in properly surely it would have some negative affect on the sound? I have not had a chance to try another meter yet. I can't use a borrowed one in case I screw that up as well.

Trev,

If you can borrow a meter with a continuity tester you can then test the probe. Check for continuity between pin 3 and the plugs. Red plug to male pin 3 on the probe and and black to female pin 3 on the socket. All other pins connect internally except pin 6. There is no connection at all on pin 6. If all tests ok then the probe is functioning correctly. If not I will send you another one. As far as the bias mod, the best way to test is to check voltage on pin 5 of the output tubes. It's a safe bet to pull all your output tubes out for this test just in case there is anything wrong with the bias supply. With the tubes pulled out power on your amp and leave the standyby switch in the standby mode. (Note: when actually testing bias with the probe and the tubes installed the amp must be in play mode) With your voltmeter set to DC volts, connect the black probe to the chassis and the red probe to pin 5 of the output tube socket. Stock reading should be -38 volts. When you turn the trimpot on the bias mod that reading should change. If it does not change then I would look for a bad solder joint like Charles suggested. A word of caution here as I just installed one for a customer and had this problem. The resistor that gets changed shares a ground connection with the cathodes of the phase inverter tube. While I was installing my kit, the ground trace lifted under the board. Although the bias mod worked fine the voltages on the phase inverter went through the roof due to the lost ground connection on the cathodes. Although the amp still worked the power output was drastically reduced and as I turned up the volume, the amp just got worse and worse.


This is just something I recently ran into and wanted to share with everyone.

Thanks
John

John, I tried the test you detailed above using the DCV meter set at 200. I got a result of 31.7 volts. I turned the bias pot in each direction to see if the reading changed and it did, but I had to turn it several rotations to get a whole volt of movement. To get to the stock reading of 38 I estimate I would have to turn it 30 times. This seems like a lot. Is this normal? I don't know how the bias potentiometer works. Can you turn it an infinite amount of times and the reading keeps going Up (or down)? Before installing it, I did match it to the resistor that was removed like you say in your instructions. If the voltage is way off, could this be why my Stiletto sounds - er - un inspiring?

Trev,

That is not normal. The bias pots are 25 turn pots so the adjustment will be gradual but not that gradual like your experiencing. The way it works is the less negatve voltage, the hotter your tubes are idling. This will definatly have effect on your tone. If they are idling to hot the amp will break up easier and you run the risk of burning up your tubes. Make sure the plates are not glowing red. I would suspect a bad connection at the wires on the circuit board like Charles mentioned. The fact that you were able to adjust and match the original resistor value indicated the bias mod is functioning correctly before installation. Not sure what current your getting but -31 volts could be to hot of a setting. -38 volts should be somewhere around the middle of the sweep of the pot and allow plent of adjustment up or down.

THanks
John

Trev,

That is not normal. The bias pots are 25 turn pots so the adjustment will be gradual but not that gradual like your experiencing. The way it works is the less negatve voltage, the hotter your tubes are idling. This will definatly have effect on your tone. If they are idling to hot the amp will break up easier and you run the risk of burning up your tubes. Make sure the plates are not glowing red. I would suspect a bad connection at the wires on the circuit board like Charles mentioned. The fact that you were able to adjust and match the original resistor value indicated the bias mod is functioning correctly before installation. Not sure what current your getting but -31 volts could be to hot of a setting. -38 volts should be somewhere around the middle of the sweep of the pot and allow plent of adjustment up or down.

THanks
John

Trev57 said:

John, I tried the test you detailed above using the DCV meter set at 200. I got a result of 31.7 volts. I turned the bias pot in each direction to see if the reading changed and it did, but I had to turn it several rotations to get a whole volt of movement. To get to the stock reading of 38 I estimate I would have to turn it 30 times. This seems like a lot. Is this normal? I don't know how the bias potentiometer works. Can you turn it an infinite amount of times and the reading keeps going Up (or down)? Before installing it, I did match it to the resistor that was removed like you say in your instructions. If the voltage is way off, could this be why my Stiletto sounds - er - un inspiring?

Click to expand...

trev-

any luck?

Well, I have looked at my soldered joints for the mod kit to the board, and they are rock solid. After reading Johns post about the ground connection hidden behind the circuit board that comes loose when you remove the resistor, I am reluctant to reheat the joints unless I am certain they are the problem. I now have to buy a new meter as it seems I have screwed up the old one that gave me reliable service for years. I also just spent all my spare budget (and then some) on the Mark V I bought, so getting a decent meter is currently out of the question. I am sure I will get it done, but right now I feel like it was a mistake and more trouble than it is worth.

I spent a bit of time this afternoon and resoldered the joints onto the circuit board. I really just moved them with a freshly tinned and pointed iron. I am sure they are good. The negative voltage readings at pin 5 are still exactly the same. I turned the bias pot 20 turns clockwise until it started clicking and got a -25.5 volt reading, then turned it 25 turns anticlockwise and got -33.7 volts. The same on all 4 valve sockets. John seems to be suggesting that my cheap meter is not up to the job, so I am reluctant to replace it with a similar one. Fluke meters appear to be top of the line, but I don't want to spend £125.00 on a meter. So can anybody suggest a decent quality mid priced unit that will do the job? What brand meters are you guys using?

Trev57 said:

I spent a bit of time this afternoon and resoldered the joints onto the circuit board. I really just moved them with a freshly tinned and pointed iron. I am sure they are good. The negative voltage readings at pin 5 are still exactly the same. I turned the bias pot 20 turns clockwise until it started clicking and got a -25.5 volt reading, then turned it 25 turns anticlockwise and got -33.7 volts. The same on all 4 valve sockets. John seems to be suggesting that my cheap meter is not up to the job, so I am reluctant to replace it with a similar one. Fluke meters appear to be top of the line, but I don't want to spend £125.00 on a meter. So can anybody suggest a decent quality mid priced unit that will do the job? What brand meters are you guys using?

Click to expand...

how does it sound? have u tried playing it? sorry to hear about your difficulties in installing this.

Trev,

I think your misinterpereting what I said. You inexpensive meter should work fine when used properly but with the pics you sent me you clearly did not use it correctly. It is possible you damaged it and there are easy ways to check that. Just take other measurments to see if it functions properly. Measure a loose resistor, measure the power at your wall outlets, etc. See if the meter is functioning properly. On thing you should not do ever is change settings while the meter probes are hooked up taking a measurment.

Now on another note the pots are 25 turn stop to stop. When you turn them until they click you are passed it's max turning range. That means 25 turns from end to end, not 25 turns from wherever your at. I think your in over your head and just causing more damage. You said you were able to match the trimpot to the original resistor value (I always set them there before shipping anyway) which would give you the -38 volts so the kit worked when you recieved it. If you turned it past it's stops to the point you hear clicking like you said then you almost definatly damaged the trimpot. You need to stop and get professional help before you do some real damage. Those trimpots are a high quality Bournes Cermet Trimmers but electonic components are delicate.

I'm still here to help!

Thanks
John

Finally!! I got a result. I did buy a new meter and it appears that the meter was the problem. So I set the bias to just under 39mA based on what I have read so far above. I was using a Strat with Van Zandt Rock pickups to test with, which is not a guitar I would use to assess a Stiletto, or any other trebly sounding amp, but I could imediately hear that something had changed drastically. So I went indoors and got my favourite tone machine (Jackson SLATQM with Tom Anderson humbuckers) and while I was away I think someone snuck into my studio and threw the piece of junk I have been living with for the last 18 months out, and replaced it with a proper amp! kidding aside, the transformation is unbelievable. I know I have been a bit negative whilst trying to get this mod to work, and I probably need to apologise to John, but this is just a different amp completely. It has gone from being an amp that I just didn't want to play, to an amp that I cannot turn off. The character of every mode is different, in fact I would say 'night and day'. Finally I can get a stunning lead sound out of channel 2 (tight gain). I still find Fluid Drive a bit muddy, but I certainly now have 2 proper useable channels on this amp. I bought the Mark V with a view to selling this off to some unsuspecting punter, but now I think they would have to pry it out of my hands. I am now going to have to sell some other stuff in order that I can keep both of these. The tones are now positively vintage. Exactly what I hoped (and initially expected) the Stiletto would be. I now have to re ask the question that I put in the other post on this subject. If this amp has this increadible tone potential that I am now hearing, what the hell are Mesa doing sending them out biased the way they are. Because in the end I would trade all the Modes, Rectifiers, Diodes, Bolds and Spongies for one great tone worthy sound???

So, my apologies to John for my attitude, and thanks for the help fixing my amp.

Trev,

That's so good to here. No need to appologize. Your frustration was understandable. I just want you and everyone to know that once you buy a product or service from me your not ever on your own. I am always here to help in every way possible.

Thanks again to everyone

John

Trev57 said:

Finally!! I got a result. I did buy a new meter and it appears that the meter was the problem. So I set the bias to just under 39mA based on what I have read so far above. I was using a Strat with Van Zandt Rock pickups to test with, which is not a guitar I would use to assess a Stiletto, or any other trebly sounding amp, but I could imediately hear that something had changed drastically. So I went indoors and got my favourite tone machine (Jackson SLATQM with Tom Anderson humbuckers) and while I was away I think someone snuck into my studio and threw the piece of junk I have been living with for the last 18 months out, and replaced it with a proper amp! kidding aside, the transformation is unbelievable. I know I have been a bit negative whilst trying to get this mod to work, and I probably need to apologise to John, but this is just a different amp completely. It has gone from being an amp that I just didn't want to play, to an amp that I cannot turn off. The character of every mode is different, in fact I would say 'night and day'. Finally I can get a stunning lead sound out of channel 2 (tight gain). I still find Fluid Drive a bit muddy, but I certainly now have 2 proper useable channels on this amp. I bought the Mark V with a view to selling this off to some unsuspecting punter, but now I think they would have to pry it out of my hands. I am now going to have to sell some other stuff in order that I can keep both of these. The tones are now positively vintage. Exactly what I hoped (and initially expected) the Stiletto would be. I now have to re ask the question that I put in the other post on this subject. If this amp has this increadible tone potential that I am now hearing, what the hell are Mesa doing sending them out biased the way they are. Because in the end I would trade all the Modes, Rectifiers, Diodes, Bolds and Spongies for one great tone worthy sound???

So, my apologies to John for my attitude, and thanks for the help fixing my amp.

Click to expand...

trev-

this is just great to hear. I'm glad that you got it worked out. Can you share more of your experience with this? What are some more positive details that you are finding with this new bias adjustment? anything u dont like? and by any chance where u able to get a bias reading of your amp before you upped it to 39mA?

Unfortunately I didnt' take a bias reading before making the change. I wish I had just for comparison reasons. But in truth, I was so disatisfied with the sound of the stock Stiletto, I was ready to get rid of it at any cost. My initial reaction towards the revised amp is that I am just incredulous at how Mesa ship them out as they are. I know this is a Mesa forum, and therefore most people are biased (no pun intended) in favour of their products, and generaly don't react towards negative comments, but since buying my Stiletto, my research generally gave me the impression that a lot of customers who bought the Stage 1 were disatisfied. I also got the impression that Mesa panicked a bit at this reaction and developed the Stage 2 to satisfy Rectifier owners and possibly compromised the amp in other ways. I have not played through a Stage 2, but it was clear from my attempts to sell my Stage one, that nobody wanted them. I am not a Boogie hater by any means. I recently bought a Mark V and I love it. This is my 4th Mesa amp all owned here in England (I lived in the States for 15 years and always played Marshall). I love the design elements and attention to detail on my Mesa gear. The options they give you are terrific for technical types who like to twiddle with their sound. And the build quality is second to none. I now have the dilema of having bought the Mark V to replace the Stiletto, only to resolve my issues with the Stiletto beyond my expectations. I have only played around with it at home so far, but I will take it to band rehearsal this week, but I wil feel obliged to take the Mark V as well. The Guys will think I am showing off, but I can't wait to compare them in a real band environment.

Back to the mod. If you read through John Mansfields posts above (and elsewhere) I think there are a lot of good tips for people contemplating the mod themselves. There are also a couple of warnings to be had, and a couple of things that probably should be pointed out in the instructions. Having said that, I did this myself having no knowledge of electronics, but I am very good at detail work and have done a lot of guitar wiring (pickups, mini switches etc.) I have also wired houses and cars from scratch so I feel I am capable. My knowledge fell down on the meter and its different scales. The change to the amps tonal characteristics for me has been drastic. It really is as if a completely different amp has replaced the thing I had before. For some time the Stiletto was the only amp I had, and I always came away from rehearsals and gigs feeling let down by it. The tone was every bad comment you ever read about them and more. Now the guitar just sounds delicious to my ears, even at low volumes. Before I could not get a lead sound from either channel in any mode. I tried all the pedals and ended up using my Fat Sandwich in front of the clean sounds to get something useable. Having been a Marshall user for years, and recently gigged for a year with a Cornford Mark 50 MKII I know what a good amp sounds like on full chat. I actually feel at the moment like the Stiletto is going to top those amps when I get to crank it up a bit this week - no pedals required.