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 How do you bias the Alchemist? 
geodude
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Joined: 31 Mar 2009
Posts: 1
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I just purchased an Alchemist and I'm trying to figure out how to bias the power tubes. The best I can figure the resistors labeled: R9 & R10 are the bias adjustments. Since the circuit looks symmetrical I'm assuming there is a separate bias adjustment for each tube.

To be sure I called technical support. Technical support said they will only give this information to a registered service center but I should know that the Alchemist is not a "typical DC bias amp".


Does anyone know for sure?

Thanks
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 Re: How do you bias the Alchemist? 
blimpo
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Joined: 15 Mar 2009
Posts: 5
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geodude wrote:
I just purchased an Alchemist and I'm trying to figure out how to bias the power tubes. The best I can figure the resistors labeled: R9 & R10 are the bias adjustments. Since the circuit looks symmetrical I'm assuming there is a separate bias adjustment for each tube.

To be sure I called technical support. Technical support said they will only give this information to a registered service center but I should know that the Alchemist is not a "typical DC bias amp".


Does anyone know for sure?

Thanks


I was wondering the same thing.

I hope someone responds with info...
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Tom M
Level I

Joined: 25 Jun 2009
Posts: 128
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trim pots for each tube, 35mA


Last edited by Tom M on Tue Feb 23, 2010 12:41 am; edited 5 times in total
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bognerandy
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Joined: 03 Nov 2009
Posts: 1
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Hello,

I have also the Bogner Alchemist 112 combo. I have had it a little over year now. Works fine. And I also have thought about biasing and it´s advantages and on the other hand do I really need to learn how to do it... Well I bought a matched pair of JJ 6L6GC power tubes and simply removed the Ruby Tubes 6L6GCM-STR (that have began to loose some of the power and touch, great tubes though but I cannot get them here) and put the new JJ ones in. To my ears the amp really sounds good and the amp kicked to different level without any kind of biasing! I am basically thinking about the tube life although some effects may be also to the sound. I think it is fairly subjective. If you use matched pair of tubes the tolerance is better and you can get decent sound without tweaking and for example won´t have to disassemble the whole thing...
So to my mind the biasing isn´t always necessary, maybe then if you want to experiment more and for example change all tubes at once, then the biasing must be done?!? I have read some about this and seen the tolerances that they use in different amps with tubes in mA values and I think it is pretty much the same.
Here is good links to see the biasing if you are interested in learning and doing it! In those videos to my opinion some of the tubes were almost the same value when plugged in/measured so I am not so sure what it really does if another tube goes up and another goes down Confused

http://www.eurotubes.com/euro-Generic-Bias.htm
http://www.eurotubes.com/euro-video.htm

I´ll let you know later what happened to my tubes without biasing... I forgot to mention this that the Ruby Tube originals had these values in sticker : PC 44 and TC 3300.
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mikevas
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Joined: 15 Apr 2010
Posts: 1
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Hello,

I just replaced the 6L6GC's with JJs and would like to bias the amp correctly and also check that everything is ok.

Someone suggested to set the current to 35mA. Is that the reading from the little 3 pin "BIAS TEST" socket? Left pin left tube, right pin right tube, middle pin ground? Is that on the 40W or 20W setting?

I read 503 Volts on the OT CENTER. Is that normal? It looks a bit too much!

Thanks!
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sahlomonic
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Joined: 11 Apr 2010
Posts: 17
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Sounds like the bias pins are laid out the same as on a Marshall JCM2000. I haven't looked into it myself, but I am curious since I want to re-tube my Alchemist here in a week or so.
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All
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Joined: 13 Mar 2010
Posts: 3
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Hello,

I purchased an Alchemist head and stack 2 months ago and didn’t had any problems with it yet…! I really like the different sounds and textures that this amp can give me. It’s definitely a keeper. I noted the volume difference between channels and also thinking of changing the original tubes for better quality ones.

A guitar builder told me he had the Alchemist analyzed by an Amp tech and was told that overall, the amp is very similar to the Bogner Custom Shop line except that the board is a little bit thinner and they don’t use Mercury Magnetic transformers but lower quality ones. He told me he changed the original tubes for Mullard’s and installed a 12at7 in the de V4 position instead of a 12ax7. He say that this smoothed the saturation on the high gain position of channel 2. He still has the channels switching issue….

I am sure that there are a lot of good technicians writing on this site and eventually someone will come up with photos or a link to a document showing how to bias the tubes and what equipment is needed to do so.

I read that some people had issue with channels switching and total loss of power. Since the warranty on those amps is not eternal, it would be great if Bogner or Line 6 or any qualified and knowledgeable Technician could come up with the most commons issues with the Alchemist and what are the applicable solutions.

I am convinced that globally this amp is of good quality and some times just some simple parts can be changed and upgraded to end up with a nearly perfect amp !

Thanks for all you info,

Really nice site.

All
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 biasing? 
tcostanada
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Joined: 13 Feb 2010
Posts: 5
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I am not sure if you meant to post this in the "biasing" section but, at least in my case, there are quite a few guitar shops that do Line6 repair facilities in my state. That means they have the schematic. I don't think most places even charge when you buy tubes from them because they know that AB amps will require it. Yeah, it be nice to know how to do it yourself but at the same time the fact that you have to disassemble the amp and can get this service for free is enough reason not to for this to be a priority.




All wrote:
Hello,

I purchased an Alchemist head and stack 2 months ago and didn’t had any problems with it yet…! I really like the different sounds and textures that this amp can give me. It’s definitely a keeper. I noted the volume difference between channels and also thinking of changing the original tubes for better quality ones.

A guitar builder told me he had the Alchemist analyzed by an Amp tech and was told that overall, the amp is very similar to the Bogner Custom Shop line except that the board is a little bit thinner and they don’t use Mercury Magnetic transformers but lower quality ones. He told me he changed the original tubes for Mullard’s and installed a 12at7 in the de V4 position instead of a 12ax7. He say that this smoothed the saturation on the high gain position of channel 2. He still has the channels switching issue….

I am sure that there are a lot of good technicians writing on this site and eventually someone will come up with photos or a link to a document showing how to bias the tubes and what equipment is needed to do so.

I read that some people had issue with channels switching and total loss of power. Since the warranty on those amps is not eternal, it would be great if Bogner or Line 6 or any qualified and knowledgeable Technician could come up with the most commons issues with the Alchemist and what are the applicable solutions.

I am convinced that globally this amp is of good quality and some times just some simple parts can be changed and upgraded to end up with a nearly perfect amp !

Thanks for all you info,

Really nice site.

All
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Tom M
Level I

Joined: 25 Jun 2009
Posts: 128
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Guys that are looking to retube and bias there amps for the Bogner Alchemist, here you go.

Buy whatever kind of 6l6gc power tubes you want and I recommend changing out the 12ax7's also.

Step 1. Remove the chassis from the head by unscrewing the 4 screw's in the top. The chassis will slide right out the back. This is the same for Every Bogner Alchemist!!

Step 2. IF you look directly at the top middle of inside the chassis you will see the bias test point, 3 pin test point. left pin=left tube right pin=right tube and middle is ground. You can also buy a little tube socket bias thing that goes in between your tube socket and your tube and when you turn the screw's on the little blue trim pots you can see the number of mV go up and down.

Step 3. Decide if your going to use just a multimeter or one of those bias gadgets I just described above, I personally just use a multimeter because that way you don't have to keep taking off the tube gadget and swapping to other tube to adjust trim pots again and repeat process, with a multimeter you hold the black lead from multimeter to middle pin and the red lead to the right or left pin. right below where you have your leads on the chassis there are 2 blue square trim pots, those are what you use to make the bias of the tube go up and down, you will get used too how much you need to turn the screw to make an adjustment after awhile of doing it, you don't have too turn them that much.

Step 4. Ok, so you have your lead's on test pins and your multimeter is on and facing you, you want your multimeter set to the range of 2 vdc if your using black and red leads from meter, if you are using the bias probe gadget you want to un plug your leads and plug your bias probe into the tube socket then put tube back in bias probe, then plug the leads from bias probe into your multimeter and set it too the 200m range. You will see what I'm talking about, everyone's meter is different ..


Last edited by Tom M on Mon May 03, 2010 11:04 pm; edited 3 times in total
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Tom M
Level I

Joined: 25 Jun 2009
Posts: 128
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step 5. I always make sure that the chassis is plugged into a speaker load or a dummy load on an attenuator, you can seriosly damage your amp. Also make sure to turn all of your volume knobs down to zero. Make sure to let the amp warm up for a couple minutes. Then select the 40 watt side, it doesn't really matter but I always do it in 40 watt side because it is a 40 watt amp and that was how I was told from respectable amp techs.

Step 6. So your leads are touching the pins and you see reading on your mm, you want to take a screwdriver and turn the screw on the square blue trim pot until you get the tube you are working on too 35mV.
So if you turn the screw clockwise it will make the bias of the tube go up and counterclock will make it go down, this is where you will see that using just a multimeter is easier, you can turn the screw, set one tube for 35mV, the other tube will go out of spec for a second then you just move your red lead to the other test pin and do the same process until both are reading 35mV, if you get 34.8 that is fine, remember they move. IF you were using one of the bias probes you would have to shut the amp down, wait to cool, switch to the other tube and do whole process over.

IF you follow these directions and you should already have a sense on what your doing in the first place you will be fine, and loving this amp. I can honestly say these amps are set cold from the factory and when I did mine the first time it sounded so warm and responsive. I am sick right now so if I left anything out, let me know but you should be good to go by following these instructions.

DONT TOUCH ANYTHING INSIDE THE AMP OTHER THAN YOUR TEST PINS,, IF YOU SLIP AND TOUCH A CAP AND YOUR OTHER HAND IS NOT IN YOUR POCKET YOU WILL GET ELECTROCUTED, DON'T BE CARELESS WHEN DEALING WITH AN AMP CHASSIS, OTHER THAN THAT HAVE FUN AND HAVE AT IT!!!


Last edited by Tom M on Sat May 01, 2010 11:05 pm; edited 2 times in total
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Tom M
Level I

Joined: 25 Jun 2009
Posts: 128
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I wouldn't neccesarily calls these steps bible but they are the flow of how i get going when doing it.

You should already be pretty versed at doing things like this if your even thinking about it, if not you can really hurt or even kill yourself. I cannot say this enough. IF you have no experience spend the money and call an amp tech, it's not worth killing yourself or ruining your amp over it.

ONe of these day's when I feel better and if I still have my alchemist I will do a youtube vid on how to bias it. Great amp once setup up right for what it does.
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 biasing instruction 
Benny123
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Joined: 10 Feb 2010
Posts: 15
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Thanks for the instruction on biasing. Though I have had my tubes biased the last time I had it re-tubed, it is nice how to do it.


Regarding the retarded users and misinterpretation question I think you know where that originates from.
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 careful with this one 
tcostanada
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Joined: 13 Feb 2010
Posts: 5
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Yeah he is bitter that I confronted his flaming. I'm sure that why that "retarded/thrpwn out of proportion" comment was thrown in there He said all this negative stuff about eurotubes after initally praising them a while back in a previous thread. i expl'd I couldnt understand what tubes he liked and so forth ant then he went back and erased al his remarks. Then he acted like he had no idea what he just wrote. See his posts that say edited 5 times and so forth?

Like i mentioned in a previous post, at least in my case, when I bought new power tubes they bias for free. Plus, it is pretty simple for a non-Line 6 dealer to become one and get the schematic.

Though his biasing instructions look straight forward I wouldn't trust 'em


Tom M wrote:
Guys that are looking to retube and bias there amps for the Bogner Alchemist, here you go.

Buy whatever kind of 6l6gc power tubes you want and I recommend changing out the 12ax7's also. I will never again offer or endorse a certain tube type or company again here, not because of the company but retarded people on this forum taking things the wrong way.

Step 1. Remove the chassis from the head by unscrewing the 4 screw's in the top. The chassis will slide right out the back. This is the same for Every Bogner Alchemist!!

Step 2. IF you look directly at the top middle of inside the chassis you will see the bias test point, 3 pin test point. left pin=left tube right pin=right tube and middle is ground. You can also buy a little tube socket bias thing that goes in between your tube socket and your tube and when you turn the screw's on the little blue trim pots you can see the number of mV go up and down.

Step 3. Decide if your going to use just a multimeter or one of those bias gadgets I just described above, I personally just use a multimeter because that way you don't have to keep taking off the tube gadget and swapping to other tube to adjust trim pots again and repeat process, with a multimeter you hold the black lead from multimeter to middle pin and the red lead to the right or left pin. right below where you have your leads on the chassis there are 2 blue square trim pots, those are what you use to make the bias of the tube go up and down, you will get used too how much you need to turn the screw to make an adjustment after awhile of doing it, you don't have too turn them that much.

Step 4. Ok, so you have your lead's on test pins and your multimeter is on and facing you, you want your multimeter set to the range of 2 vdc if your using black and red leads from meter, if you are using the bias probe gadget you want to un plug your leads and plug your bias probe into the tube socket then put tube back in bias probe, then plug the leads from bias probe into your multimeter and set it too the 200m range. You will see what I'm talking about, everyone's meter is different ..
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All
Newbie

Joined: 13 Mar 2010
Posts: 3
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Tom M wrote:
I wouldn't neccesarily calls these steps bible but they are the flow of how i get going when doing it.

You should already be pretty versed at doing things like this if your even thinking about it, if not you can really hurt or even kill yourself. I cannot say this enough. IF you have no experience spend the money and call an amp tech, it's not worth killing yourself or ruining your amp over it.

ONe of these day's when I feel better and if I still have my alchemist I will do a youtube vid on how to bias it. Great amp once setup up right for what it does.


Hello Tom,

Thanks for your very instructive comments ! Looking foward to the video or photo documented instructions.

Very constructive ! This is what a forum is all about !

All
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Tom M
Level I

Joined: 25 Jun 2009
Posts: 128
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I live in a pretty decent size city, if you go into a musicstore to buy tubes and then say "oh wait, hold on let me grab my amp your going to do this for free." I don't think so, a matter of fact, you'll probably get laughed at. This is how amp techs make money, no freebies on amp biasing unless you know a friend.


THe BIas instructions are black and white, if you think there is sublimminal crap in there, then don't do it. Otherwise it may help somebody out. These directions are more geared for guy's that already have chassis open and have a feel for what there doing but may have a quick question while inside, like oh what bias do I need, or which way do I turn the screw for getting closer to my goal. That's all. Enjoy.


Last edited by Tom M on Mon May 03, 2010 11:06 pm; edited 1 time in total
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