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Post by LordToneKing on Sept 16, 2009 20:20:40 GMT -5
I just tried to put a quad of Tung Sol EL34B's in my amp tonight. When I hooked up the weber it read 19ma, so I turned the bias pot until it maxed out and it only went up to 24ma  I put in an old old set of Mullards and it went to 26ma...maxed once again Then my buddy had some winged c's that were at 32ma and sounded really good...but the bias trim was maxed The TS tubes were rated at 27ma, bought from Doug's Tubes. Do you think that the tubes were just too cold for my amp?...as were the Mullards? The winged C's fell into range but I cant figure why my bias screw is maxing out. It sort of clicks when it's maxed, is that the way it's supposed to be?? I'm wondering if I buy tubes at 40ma-45ma if my bias trim will have room on both sides (hot and cold) |
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Post by jesusdriven on Sept 16, 2009 20:55:22 GMT -5
I just tried to put a quad of Tung Sol EL34B's in my amp tonight. When I hooked up the weber it read 19ma, so I turned the bias pot until it maxed out and it only went up to 24ma I put in an old old set of Mullards and it went to 26ma...maxed once again Then my buddy had some winged c's that were at 32ma and sounded really good...but the bias trim was maxed The TS tubes were rated at 27ma, bought from Doug's Tubes. Do you think that the tubes were just too cold for my amp?...as were the Mullards? The winged C's fell into range but I cant figure why my bias screw is maxing out. It sort of clicks when it's maxed, is that the way it's supposed to be?? I'm wondering if I buy tubes at 40ma-45ma if my bias trim will have room on both sides (hot and cold) I know that the bias adjustment screw on the amp can run out of travel, but I think there should be enough movement to handle most EL34 tubes. The tubes could be too low, but I would check with Scott to get his opinion. Your Weber might not be real accurate so that won't help matters either in getting a correct reading. I have a Weber and my plate voltage reading are off by 2ma. Scott told me that the plate voltage will not change from tube to tube. He said that is showing the difference in resistor values on my Bias Rite meter. Basically my Bias rite reads 2ma low. I biased my QR for two tubes at 50 watts with one tube at 30ma and the other at 34ma. I sent the amp to Scott for a problem that turned out to NOT be amp related. Scott checked the bias and it was 28ma and 32ma. This confirmed that my Bias Rite is 2ma off. I have heard of some of them being off by up to 5ma. I would ask Scott what he thinks. If your plate voltage readings are varying 4 or 5ma from tube to tube than I believe that is showing you a variance in its accuracy. Your 24ma tube could actually be maxing out at 29ma. Some cold tubes will not go much higher than that without pulling the others out of range. |
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Post by jesusdriven on Sept 16, 2009 21:01:55 GMT -5
Man JesusDriven I would be in heaven ( no pun intended) if you could post a video of biasing a Splawn. I watched the Eurotube video and it made zero sense to me. I don't know ANYTHING about the inside of an amp. Besides swappint preamp / power tubes on my Mesa DR I have never done anything more. I am very apprehensive to try biasing for fear that I will make toast of myself. I wish I had some video equipment. Maybe I will get some and do that someday. I have a jeweler's screw driver wrapped in electrical tape with just the tip exposed. I am very CAREFUL to not touch anything inside the amp other than the bias screw at anytime; powered up or not because capacitors store a charge. I copied and pasted a part of a past thread on biasing in which I gave an explanation on how I bias my amp. It is really pretty easy. Just don't let yourself get careless when you do it. How To Bias Your Amp: I am not an electrician and I found biasing my own amp to be a daunting task before I did it. I put down a blanket in my garage and flip the amp head upside down to take out the four screws (I loosen them first) that hold in the chassis. I then CAREFULLY slide the amp out while it is upside down on the blanket. I also have a shelf board that I cut a section out of to access the bias screw. I put the shelf board across a couple storage bins like a bridge and set the amp on it. I always remove my power tubes before I flip the amp, and take the amp out of the head box. Once you have the amp set on the shelf, connect your tubes to your Bias Rite adapters. You will then insert them into the tube sockets on your amp. ALWAYS plug your amp into the speaker cabinet since it needs to see a load. You will fry your transformer if your amp gets turned on when it is not plugged into a speaker cabinet. Now put power to your amp and turn it on. Turn on your Bias Rite and check the readings. They will go high at first and then come down some. You are taking and average between your tubes. If you have one that reads 29ma and another that reads 33ma, then the average is 31ma. Set your bias and then let your amp run for 3 or 4 hours before making further adjustments to allow the tubes time to settle into a place where they are comfortable. Give it another 30 minutes or so after that to see if the setting holds. I turn my amp off after that and let it sit for 25 minutes to give the tubes time to cool off before removing them. I also note what tubes came out of what sockets. Once my amp is back together I install the tubes and back panel. She is now ready to be fired up! |
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Post by jesusdriven on Sept 16, 2009 21:17:36 GMT -5
Thanks for all the info here. a great read. I am going to buy one of those bias testers. either the bias king or the compu bias. any idea which tester is better?? I will most likely buy tubes from Scott. mainly because I will want to continue doing biz with him and I would rather buy from him than other places. but It will be cool to learn how to bias my amp. that way I know its good. and I can use the tester to bias my old Laney and My Marshall rack power amp as well. lots of good info here fellas!!!!! I will probably get a Compu Bias if I get something else because I have heard real good things about it. I would go for a Compu Bias I were you. They cost a little more than the Weber, but it sounds like they are worth the extra cash. |
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Post by tonemonster on Sept 16, 2009 21:29:46 GMT -5
I like the idea of the screwdriver wrapped in electrical tape for safety. so where is the bias pot on these amps? is it on the top of the chassis where the tubes are? or underneath the chassis where the cuircut board is???
and are their one or two bias pots? is there one for each set of two tubes?
and does scott list how to do this in the owners manual??? how do you know what values you are supposed to bais too??
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Post by stratkiller51 on Sept 16, 2009 22:11:01 GMT -5
i got my bias screwdriver at sears, its @5 inches long and has a plastic or rubber handle with a the very top that turns freely @ $6
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Post by splatter on Sept 16, 2009 22:24:23 GMT -5
Man JesusDriven I would be in heaven ( no pun intended) if you could post a video of biasing a Splawn. I watched the Eurotube video and it made zero sense to me. I don't know ANYTHING about the inside of an amp. Besides swappint preamp / power tubes on my Mesa DR I have never done anything more. I am very apprehensive to try biasing for fear that I will make toast of myself. I wish I had some video equipment. Maybe I will get some and do that someday. I have a jeweler's screw driver wrapped in electrical tape with just the tip exposed. I am very CAREFUL to not touch anything inside the amp other than the bias screw at anytime; powered up or not because capacitors store a charge. I copied and pasted a part of a past thread on biasing in which I gave an explanation on how I bias my amp. It is really pretty easy. Just don't let yourself get careless when you do it. How To Bias Your Amp: I am not an electrician and I found biasing my own amp to be a daunting task before I did it. I put down a blanket in my garage and flip the amp head upside down to take out the four screws (I loosen them first) that hold in the chassis. I then CAREFULLY slide the amp out while it is upside down on the blanket. I also have a shelf board that I cut a section out of to access the bias screw. I put the shelf board across a couple storage bins like a bridge and set the amp on it. I always remove my power tubes before I flip the amp, and take the amp out of the head box. Once you have the amp set on the shelf, connect your tubes to your Bias Rite adapters. You will then insert them into the tube sockets on your amp. ALWAYS plug your amp into the speaker cabinet since it needs to see a load. You will fry your transformer if your amp gets turned on when it is not plugged into a speaker cabinet. Now put power to your amp and turn it on. Turn on your Bias Rite and check the readings. They will go high at first and then come down some. You are taking and average between your tubes. If you have one that reads 29ma and another that reads 33ma, then the average is 31ma. Let your amp run for 3 or 4 hours before making the adjustment to allow the tubes time to settle into a place where they are comfortable. Give it another 30 minutes or so after that to see if the setting holds. I turn my amp off after that and let it sit for 25 minutes to give the tubes time to cool off before removing them. I also note what tubes came out of what sockets. Once my amp is back together I install the tubes and back panel. She is now ready to be fired up! JD sounds like you go to way to much trouble IMO. I fire the amp up let it warm up for 30 seconds .Flip it off of standby wait about 5 minutes take the readings bias the amp and power it down snatch the tubes wearing gloves while they are still hot . take the bias probe out put the tubes back in and I'm done .All in about 20 minutes. my probe only has 2 sockets so I have to do 2 at a time . Tubes reach there full operating temp within a couple of minutes so I really don't see the advantage of running it for hours before you bias it . But everybody does things different  |
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Post by jesusdriven on Sept 16, 2009 22:45:55 GMT -5
I wish I had some video equipment. Maybe I will get some and do that someday. I have a jeweler's screw driver wrapped in electrical tape with just the tip exposed. I am very CAREFUL to not touch anything inside the amp other than the bias screw at anytime; powered up or not because capacitors store a charge. I copied and pasted a part of a past thread on biasing in which I gave an explanation on how I bias my amp. It is really pretty easy. Just don't let yourself get careless when you do it. How To Bias Your Amp: I am not an electrician and I found biasing my own amp to be a daunting task before I did it. I put down a blanket in my garage and flip the amp head upside down to take out the four screws (I loosen them first) that hold in the chassis. I then CAREFULLY slide the amp out while it is upside down on the blanket. I also have a shelf board that I cut a section out of to access the bias screw. I put the shelf board across a couple storage bins like a bridge and set the amp on it. I always remove my power tubes before I flip the amp, and take the amp out of the head box. Once you have the amp set on the shelf, connect your tubes to your Bias Rite adapters. You will then insert them into the tube sockets on your amp. ALWAYS plug your amp into the speaker cabinet since it needs to see a load. You will fry your transformer if your amp gets turned on when it is not plugged into a speaker cabinet. Now put power to your amp and turn it on. Turn on your Bias Rite and check the readings. They will go high at first and then come down some. You are taking and average between your tubes. If you have one that reads 29ma and another that reads 33ma, then the average is 31ma. Let your amp run for 3 or 4 hours before making the adjustment to allow the tubes time to settle into a place where they are comfortable. Give it another 30 minutes or so after that to see if the setting holds. I turn my amp off after that and let it sit for 25 minutes to give the tubes time to cool off before removing them. I also note what tubes came out of what sockets. Once my amp is back together I install the tubes and back panel. She is now ready to be fired up! JD sounds like you go to way to much trouble IMO. I fire the amp up let it warm up for 30 seconds .Flip it off of standby wait about 5 minutes take the readings bias the amp and power it down snatch the tubes wearing gloves while they are still hot . take the bias probe out put the tubes back in and I'm done .All in about 20 minutes. my probe only has 2 sockets so I have to do 2 at a time . Tubes reach there full operating temp within a couple of minutes so I really don't see the advantage of running it for hours before you bias it . But everybody does things different The reason I take so long is because the tubes can take 3 or 4 hours before the tubes settle into a place where the are stable. I did A LOT ;D of reading on google about biasing amps when I was figuring out this stuff. The first time I biased my amp I was done in no time, but I found that the bias had drifter much lower than how I set it when I checked it a few weeks later. I read that some amp techs don't even make an adjustment until the tubes have settled in for 3 hours. They said check the bias every 30 minutes after that to make sure it hold in place. I have set my bias a few minutes after I have turned it on, but checked 30 minutes later and found that the reading drooped like 4ma as the tubes settled into a place where they are happy operating. I normally re-adjust the bias after 30 minutes and then check every 30 minutes. They might be stable for an hour than drop a little more. I would rather spend more time when I bias in order to have to do the whole thing less often. I really baby my tubes because tubes are delicate and I don't want to go through the hassle of biasing my amp and then damage a tube by moving it when it is real hot. I try to bias my amp when I have the time to do it so I am not in a rush. I try to wait 20 minutes before moving my amp after playing live (if at all possible) in order to give my tubes a chance to cool. PS: The bias adjustment screw for those who don't know will affect all of your tubes. If one tube reads 30ma and the other reads 34ma; turning the adjustment screw (located under the chassis) to bring the 30ma tube up to 32ma will cause the 34ma tube to rise to 36ma. You can not turn the screw and bring them closer together as I thought before I ever biased an amp. Matched tubes should be within 5ma of each other. Put the hottest tubes on the outer sockets, and the cooler ones on the inside sockets. Click on the link and scroll down to see a picture of the bias screw. It is MUCH smaller than in the picture. I believe that this is Hacksaw's site and that dude REALLY knows his stuff when it comes to technical stuff. He was kind enough to give me some biasing tips when I was figuring out how to do it. He could probably build an amp in his sleep. ;D www.guitarstudio.tv/Splawn/ |
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Post by jesusdriven on Sept 17, 2009 0:23:33 GMT -5
I wish I had some video equipment. Maybe I will get some and do that someday. I have a jeweler's screw driver wrapped in electrical tape with just the tip exposed. I am very CAREFUL to not touch anything inside the amp other than the bias screw at anytime; powered up or not because capacitors store a charge. I copied and pasted a part of a past thread on biasing in which I gave an explanation on how I bias my amp. It is really pretty easy. Just don't let yourself get careless when you do it. How To Bias Your Amp: I am not an electrician and I found biasing my own amp to be a daunting task before I did it. I put down a blanket in my garage and flip the amp head upside down to take out the four screws (I loosen them first) that hold in the chassis. I then CAREFULLY slide the amp out while it is upside down on the blanket. I also have a shelf board that I cut a section out of to access the bias screw. I put the shelf board across a couple storage bins like a bridge and set the amp on it. I always remove my power tubes before I flip the amp, and take the amp out of the head box. Once you have the amp set on the shelf, connect your tubes to your Bias Rite adapters. You will then insert them into the tube sockets on your amp. ALWAYS plug your amp into the speaker cabinet since it needs to see a load. You will fry your transformer if your amp gets turned on when it is not plugged into a speaker cabinet. Now put power to your amp and turn it on. Turn on your Bias Rite and check the readings. They will go high at first and then come down some. You are taking and average between your tubes. If you have one that reads 29ma and another that reads 33ma, then the average is 31ma. Let your amp run for 3 or 4 hours before making the adjustment to allow the tubes time to settle into a place where they are comfortable. Give it another 30 minutes or so after that to see if the setting holds. I turn my amp off after that and let it sit for 25 minutes to give the tubes time to cool off before removing them. I also note what tubes came out of what sockets. Once my amp is back together I install the tubes and back panel. She is now ready to be fired up! JD sounds like you go to way to much trouble IMO. I fire the amp up let it warm up for 30 seconds .Flip it off of standby wait about 5 minutes take the readings bias the amp and power it down snatch the tubes wearing gloves while they are still hot . take the bias probe out put the tubes back in and I'm done .All in about 20 minutes. my probe only has 2 sockets so I have to do 2 at a time . Tubes reach there full operating temp within a couple of minutes so I really don't see the advantage of running it for hours before you bias it . But everybody does things different I forgot to add before that I am sure most techs bias amps real quick also, and pull the the still hot tubes out while wearing gloves just to get it out the door. The more amps they do the more money they make. I bet a lot of them take more time when they bias their own amps. |
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Post by Ayton(e) on Sept 18, 2009 11:41:02 GMT -5
Man JesusDriven I would be in heaven ( no pun intended) if you could post a video of biasing a Splawn. I watched the Eurotube video and it made zero sense to me. I don't know ANYTHING about the inside of an amp. Besides swappint preamp / power tubes on my Mesa DR I have never done anything more. I am very apprehensive to try biasing for fear that I will make toast of myself. I wish I had some video equipment. Maybe I will get some and do that someday. I have a jeweler's screw driver wrapped in electrical tape with just the tip exposed. I am very CAREFUL to not touch anything inside the amp other than the bias screw at anytime; powered up or not because capacitors store a charge. I copied and pasted a part of a past thread on biasing in which I gave an explanation on how I bias my amp. It is really pretty easy. Just don't let yourself get careless when you do it. How To Bias Your Amp: I am not an electrician and I found biasing my own amp to be a daunting task before I did it. I put down a blanket in my garage and flip the amp head upside down to take out the four screws (I loosen them first) that hold in the chassis. I then CAREFULLY slide the amp out while it is upside down on the blanket. I also have a shelf board that I cut a section out of to access the bias screw. I put the shelf board across a couple storage bins like a bridge and set the amp on it. I always remove my power tubes before I flip the amp, and take the amp out of the head box. Once you have the amp set on the shelf, connect your tubes to your Bias Rite adapters. You will then insert them into the tube sockets on your amp. ALWAYS plug your amp into the speaker cabinet since it needs to see a load. You will fry your transformer if your amp gets turned on when it is not plugged into a speaker cabinet. Now put power to your amp and turn it on. Turn on your Bias Rite and check the readings. They will go high at first and then come down some. You are taking and average between your tubes. If you have one that reads 29ma and another that reads 33ma, then the average is 31ma. Let your amp run for 3 or 4 hours before making the adjustment to allow the tubes time to settle into a place where they are comfortable. Give it another 30 minutes or so after that to see if the setting holds. I turn my amp off after that and let it sit for 25 minutes to give the tubes time to cool off before removing them. I also note what tubes came out of what sockets. Once my amp is back together I install the tubes and back panel. She is now ready to be fired up! Great! Now copy this link to your signature, label it "How to bias your Splawn" and point people there forever more! Or lobby a mod to put it in the frequently asked questions section. Or if you had pics, I could put it on my site. Good info. |
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Post by jesusdriven on Sept 18, 2009 20:15:51 GMT -5
I wish I had some video equipment. Maybe I will get some and do that someday. I have a jeweler's screw driver wrapped in electrical tape with just the tip exposed. I am very CAREFUL to not touch anything inside the amp other than the bias screw at anytime; powered up or not because capacitors store a charge. I copied and pasted a part of a past thread on biasing in which I gave an explanation on how I bias my amp. It is really pretty easy. Just don't let yourself get careless when you do it. How To Bias Your Amp: I am not an electrician and I found biasing my own amp to be a daunting task before I did it. I put down a blanket in my garage and flip the amp head upside down to take out the four screws (I loosen them first) that hold in the chassis. I then CAREFULLY slide the amp out while it is upside down on the blanket. I also have a shelf board that I cut a section out of to access the bias screw. I put the shelf board across a couple storage bins like a bridge and set the amp on it. I always remove my power tubes before I flip the amp, and take the amp out of the head box. Once you have the amp set on the shelf, connect your tubes to your Bias Rite adapters. You will then insert them into the tube sockets on your amp. ALWAYS plug your amp into the speaker cabinet since it needs to see a load. You will fry your transformer if your amp gets turned on when it is not plugged into a speaker cabinet. Now put power to your amp and turn it on. Turn on your Bias Rite and check the readings. They will go high at first and then come down some. You are taking and average between your tubes. If you have one that reads 29ma and another that reads 33ma, then the average is 31ma. Let your amp run for 3 or 4 hours before making the adjustment to allow the tubes time to settle into a place where they are comfortable. Give it another 30 minutes or so after that to see if the setting holds. I turn my amp off after that and let it sit for 25 minutes to give the tubes time to cool off before removing them. I also note what tubes came out of what sockets. Once my amp is back together I install the tubes and back panel. She is now ready to be fired up! Great! Now copy this link to your signature, label it "How to bias your Splawn" and point people there forever more! Or lobby a mod to put it in the frequently asked questions section. Or if you had pics, I could put it on my site. Good info. Your link works, but I could not get it to work once I pasted it to my signature. |
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Post by tonemonster on Sept 20, 2009 8:31:22 GMT -5
this is a great thread. one of the most informative I have ever read!!!! excellent info here!!!!  Thanks to everyone for all the great info. It keeps gettign better! |
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Post by Ayton(e) on Sept 20, 2009 13:09:24 GMT -5
Great! Now copy this link to your signature, label it "How to bias your Splawn" and point people there forever more! Or lobby a mod to put it in the frequently asked questions section. Or if you had pics, I could put it on my site. Good info. Your link works, but I could not get it to work once I pasted it to my signature. [url=http://splawnfans.proboards.com/index.cgi?board=quick&action=display&thread=6850&page=3#95531]How To Bias Your Splawn[/url] |
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Thanks to everyone for all the great info. It keeps gettign better!