Replacing power tubes - rebias?
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mikemorgan
panned out
In a word, yes.
mikemorgan
panned out
The rating listed on any given tube does not indicate how it will react in an amplifier circuit, and every tube reacts differently. Matched tubes have fewer anomalies, but should still be biased, a very simple process.
mikemorgan
panned out
The biasing procedure for every amp is different. First you must drain the capaicitors or you might DIE. This is no joke. Caps can hold 400 volts for two weeks or more. Always use the one-hand rule. Only one hand touches the amp at any time. That way the voltage probably won't shoot through your heart. Scared yet?
Once the caps are drained of current, you locate the bias pot and the bias test points. Rotate the screw in the bias pot in both directions to find the stops. Attach the leads of your multimeter to the bias points. Insert your tubes. Turn the amp on. Let is warm up to full operating temp, volume at maximum! (ONE-HAND rule, don't forget!!!) Turn the bias pot screw until you reach the desired voltage for your tubes (these numbers are part of tube chart operational listings).
This entire operation is fairly easy to do, and BEST LEFT TO A QUALIFIED AMP TECH! Ask your repairman if you can look over his shoulder and pay him whatever he asks for a tube biasing lesson. You only need to know how to re-bias YOUR amp, not every tube combo out there.
Once the caps are drained of current, you locate the bias pot and the bias test points. Rotate the screw in the bias pot in both directions to find the stops. Attach the leads of your multimeter to the bias points. Insert your tubes. Turn the amp on. Let is warm up to full operating temp, volume at maximum! (ONE-HAND rule, don't forget!!!) Turn the bias pot screw until you reach the desired voltage for your tubes (these numbers are part of tube chart operational listings).
This entire operation is fairly easy to do, and BEST LEFT TO A QUALIFIED AMP TECH! Ask your repairman if you can look over his shoulder and pay him whatever he asks for a tube biasing lesson. You only need to know how to re-bias YOUR amp, not every tube combo out there.
! I told him I didn't really know all that. Thanks again, MikeThanks Mikemorgan! I wish I had a video of someone re-biasing a 2205. What a pain...I never gig this amp and only have about 15 auditions and some jam sessions on these power tubes and now I have to put it in the shop. I have played a MK II C+ and a MK II B for the last 25 years and never had to worry about biasing my amps. But damn, this Marshall does sound awesome.
What damage can I cause if I have to replace a power tube at a gig without re-biasing? Never gig without a backup rig!
What damage can I cause if I have to replace a power tube at a gig without re-biasing? Never gig without a backup rig!
Lt. Bob
Spread the Daf!
You won't damage amything by not rebiasing.
Rebiasing is to get the very best performance out of the tubes ..... to get that last bit of sound quality and performance.
Although to do the very best it's a decent idea to rebias ..... there are plenty of amps out there that are fixed bias and can't be rebiased.
And you absolutley can just drop a tube into an amp without worrying about the bias Maybe if it's an old amp you might badly need to rebias because with age the bias can drift quite a bit ...... but even those don't always need it. I have a fairly large collection of tube amps ..... a couple that I've personally used for 30 years and in 42 years of playing through tube amps I've never rebiased an amp ever ...... not one single time. And my amps sound great.
And I've had a couple of excellent techs who I knew well enough that they told me what they might not tell the public and when I would ask about rebiasing ..... they'd just shrug their shoulders and say if I wanted to but it wasn't that big a deal usually.
I think biasing an amp every single time you drop a tube in it is one of those things that people get overwrought about.
Kinda like adjusting a truss rod. A very simple thing really, but people will freak out .... "OMG .... you'll snap the neck off!!!! "
It's possible to mess it up but only if you don't use any common sense. It's really something anyone can do ingeneral unless it's a problem neck. Same thing here..... there are times when rebiasing is a good idea but most of the time it's not as critical as people make it sound.
Rebiasing is to get the very best performance out of the tubes ..... to get that last bit of sound quality and performance.
Although to do the very best it's a decent idea to rebias ..... there are plenty of amps out there that are fixed bias and can't be rebiased.
And you absolutley can just drop a tube into an amp without worrying about the bias Maybe if it's an old amp you might badly need to rebias because with age the bias can drift quite a bit ...... but even those don't always need it. I have a fairly large collection of tube amps ..... a couple that I've personally used for 30 years and in 42 years of playing through tube amps I've never rebiased an amp ever ...... not one single time. And my amps sound great.
And I've had a couple of excellent techs who I knew well enough that they told me what they might not tell the public and when I would ask about rebiasing ..... they'd just shrug their shoulders and say if I wanted to but it wasn't that big a deal usually.
I think biasing an amp every single time you drop a tube in it is one of those things that people get overwrought about.
Kinda like adjusting a truss rod. A very simple thing really, but people will freak out .... "OMG .... you'll snap the neck off!!!! "
It's possible to mess it up but only if you don't use any common sense. It's really something anyone can do ingeneral unless it's a problem neck. Same thing here..... there are times when rebiasing is a good idea but most of the time it's not as critical as people make it sound.
Wow, awesome and thanks for the indepth reply Lt. Bob! I just want to play guitar...not worry about a bunch of tube crap, HA! I've been spoiled by my fixed bias Mesas for gigs and have always taken my stay-at-home Fenders and Marshalls to the shop for power tube replacement. I either have to say screw it and throw some tubes in there or learn how to rebias because I'm tired of this ordeal everytime a power tube shorts out or gets weak.
Thatupstateguy
New member
What both Mike, and Lt Bob said are right on the money,....
and let me add this,....
DO NOT MESS WITH ANYTHING INSIDE YOUR AMP UNLESS YOU KNOW WHAT YOU ARE DOING!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
there are LETHAL voltages runnin around in there, and if you do not know EXACTLY how to test, or adjust any of those parts,.... DO NOT ATTEMPT TO DO IT YOURSELF.....
That warning having been given,......
Changing power tubes is absoluely not a hard thing to do,.....
I, like Lt Bob.... have been around tube amps for many years,... and I have never bothered to re-bias any of the amps I have, or used to have,....
what bias does, is to adjust the voltage going to certain parts of the power tube structure.... running hot, gives you a dirtier sound, but will burn thru your power tubes in short order...... running cold will also wear them out sooner than normal,..... so having the PROPER voltage to the plates gives you the MOST for your money in terms of tube life,.....
after saying that,..... just realize that to just change tubes to another set of the same,.... you should be good to go,....
Most 'SETS' of tubes, are matched as close as possible to each other,.... but will be different sounding than say another set from a different maker....
and you do not have to stick with 'MESA' branded tubes, they are just branded that way to meet what Mesa thinks is good for their amps.
It does NOT mean you have to keep those in your amp.....
you can use groove tubes,.. or JJs, or Svetlanas, or whatever,....
They will all sound a little bit different from one another due to manufacturing differences......
the guy at Eurotubes is real good about matching up your style of playing,.... your amps tubes, and with a short conversation, can recommend several options for your particular situation.
just google Vacuum Tubes, and you will have plenty of stuff to study up on.....
otherwise,..... have fun..!!!and don't worry so much about the bias, just stick a new set in there and play...!!!!!!!!
Steve
and let me add this,....
DO NOT MESS WITH ANYTHING INSIDE YOUR AMP UNLESS YOU KNOW WHAT YOU ARE DOING!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
there are LETHAL voltages runnin around in there, and if you do not know EXACTLY how to test, or adjust any of those parts,.... DO NOT ATTEMPT TO DO IT YOURSELF.....
That warning having been given,......
Changing power tubes is absoluely not a hard thing to do,.....
I, like Lt Bob.... have been around tube amps for many years,... and I have never bothered to re-bias any of the amps I have, or used to have,....
what bias does, is to adjust the voltage going to certain parts of the power tube structure.... running hot, gives you a dirtier sound, but will burn thru your power tubes in short order...... running cold will also wear them out sooner than normal,..... so having the PROPER voltage to the plates gives you the MOST for your money in terms of tube life,.....
after saying that,..... just realize that to just change tubes to another set of the same,.... you should be good to go,....
Most 'SETS' of tubes, are matched as close as possible to each other,.... but will be different sounding than say another set from a different maker....
and you do not have to stick with 'MESA' branded tubes, they are just branded that way to meet what Mesa thinks is good for their amps.
It does NOT mean you have to keep those in your amp.....
you can use groove tubes,.. or JJs, or Svetlanas, or whatever,....
They will all sound a little bit different from one another due to manufacturing differences......
the guy at Eurotubes is real good about matching up your style of playing,.... your amps tubes, and with a short conversation, can recommend several options for your particular situation.
just google Vacuum Tubes, and you will have plenty of stuff to study up on.....
otherwise,..... have fun..!!!and don't worry so much about the bias, just stick a new set in there and play...!!!!!!!!
Steve
mikemorgan
panned out
I also agree with everything Lt Bob has said. Re-biasing is not mandatory in many cases, and impossible in some. I just don't want people to get the idea biasing isn't necessary. Improper biasing does lead to either shortened tube life or shortened tranny life. Most tranny's are beefy enough to deal with the overload and probably never burn out. I do know that a properly biased amp's tubes will last almost indefinately.
I view biasing as being meticulous about my tune-up. Changing tubes is not something I want do do very often. I could easily change the spark plugs in my car without checking the gap, but I use a feeler guage to set the gap anyway because I want the best performance from my engine, and I don't like burnt valves (no pun intended).
I view biasing as being meticulous about my tune-up. Changing tubes is not something I want do do very often. I could easily change the spark plugs in my car without checking the gap, but I use a feeler guage to set the gap anyway because I want the best performance from my engine, and I don't like burnt valves (no pun intended).
Lt. Bob
Spread the Daf!
That's certainly all valid. If you know how to do it . then why not ya' know?mikemorgan said:
But power tubes don't last indefinitely no matter how well it's biased. My main gigging amp right now is a Mesa Blue Angel and it's a class A amp. Now I know I play more than most (5 to 7 gigs a week) but I have to retube it (power tubes only since preamp tubes do last indefinitely) about once a year. It starts to lose focus ... the bass response gets poor and there's no sparkle at the top end. It's quite a dramatic change actually ...... usually I'll struggle along with it for a month or two and then finally give in and retube.
In fact I'm at that point right now ..... I have a new set of tubes sitting in my music room but I'll be damned if I'm gonna change them until the sound just sucks! ................... for three weeks in a row!!
mikemorgan
panned out
Good stuff here, guys. I can't say it enough.
DON'T MESS AROUND WITH YOUR AMP!! IT CAN KILL YOU! What a dumb way to die.
One other thing to watch for is where your tube sockets are mounted. Are they mounted to the only printed circuit board in your amp? or are they mounted on their own separate board? Overheating a PCB leads to breakdown of solder joints which have to be touched up by a tech.
DON'T MESS AROUND WITH YOUR AMP!! IT CAN KILL YOU! What a dumb way to die.
One other thing to watch for is where your tube sockets are mounted. Are they mounted to the only printed circuit board in your amp? or are they mounted on their own separate board? Overheating a PCB leads to breakdown of solder joints which have to be touched up by a tech.
mikemorgan
panned out
I hear you Bob, that's a lot of gigging, for sure.
I'll admit I didn't know much about tube swapping and biasing at all until I hired a guy who plays Mesa amps exclusively. When he told me he switched power tubes at least once a year I was shocked. He said sometimes they don't last 5 months. I told him my main rig for 25 years was an Ampeg which had never been re-tubed. I also had two Fenders in similar condition, ten years, no tubes. He got me educated. That's kinda our dig on each other now, he can't believe I can play on crappy tubes, and I can't believe he spends so much money on them.
I'll admit I didn't know much about tube swapping and biasing at all until I hired a guy who plays Mesa amps exclusively. When he told me he switched power tubes at least once a year I was shocked. He said sometimes they don't last 5 months. I told him my main rig for 25 years was an Ampeg which had never been re-tubed. I also had two Fenders in similar condition, ten years, no tubes. He got me educated. That's kinda our dig on each other now, he can't believe I can play on crappy tubes, and I can't believe he spends so much money on them.
Lt. Bob
Spread the Daf!
I'm gonna side with you on that.mikemorgan said:
It's like those guys that change strings before every single gig. Yeah ...... you can hear the difference but so what?
It's funny how the more you actually gig ..... the less you care about that stuff.
You like Ampegs? I've got (all early 70's) A VT40, a VT22 and a V-2 half stack. Don't use 'em much anymore .... the VT40 weighs 95 lbs and I'm freakin' OLD!!!
But nothing else sounds quite like them. I have a stash of 7027A's sitting around so I can retube them all twice so I figure I'm set for life on these 'cause they really don't chew up tubes very quickly.
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mikemorgan
panned out
Lt. Bob
Spread the Daf!
Yeah ..... that VT 40 is killer. Is yours with the controls on top or in front?mikemorgan said:
Mine is the on-top version. I actually bought it from a guy named Jimmy Eppard (google his name) that Dragonworks right here on this board turned me onto. It just screams ...... and when I do use it ..... I have soundmen begging me to turn it down?
Them: "For Gods' sake, turn it down"
Me: "Am I too loud in the mix?"
Them: " No you're not too loud but I don't have you in the PA at all"
Me: "
"Well, I'm no spring chicken and I've been known to gig 5-7 nights a week for many, many years is a row. But I am one of those guys who changed strings on my main axe for every new venue...about once a week...and changed power tubes at least once a year. I've always used Mesa Mark series amps for gigging because thet're small, reliable, and do the job. These days I'm loving my JCM 800 and my Bassman (jumpered!) so I'm sure I'll burn through some power tubes on both of them, like I just did on the 800, but I'm not re-biasing them unless I start burning through trannies!!!
Thanks an million guys!
Thanks an million guys!
dementedchord
Psychotic State alumni ch
$.02
geeeeeee... ya dont want to get between a guitarist and his tube amp... unless your say a tech of some 15 yrs.... HEY I"M A TECH of some 15 yrs.... and most of what i read seems to be half truths and vacillating opinion...
in answer to the original post yes you can use the same rating and expect it to work reasonably well... that being said IDEALLY ya want to rebias each time you retube an output... since someone already used an auto analogy let's stay with that... bias is like setting the idle...if it's too cold the amp doesnt respond quickly... if it's too hot they tend to burn up quickly... what you are doing is introducing a negative voltage at the tubes input to litterally shut it down... with out it the amp thermals... incedently dont think that you can just test one tube and get away with it ya really gotta do them both...
if you've been lucky so far good for you... i can remember working with a guy that insisted on doing something i told him would make it unstable... wouldnt beleive untill we had to do the last 1 1/2 set as a trio... btw ask the big guys if they rebias.... i did some soldanos for VAI once.... YMMV
geeeeeee... ya dont want to get between a guitarist and his tube amp... unless your say a tech of some 15 yrs.... HEY I"M A TECH of some 15 yrs.... and most of what i read seems to be half truths and vacillating opinion...
in answer to the original post yes you can use the same rating and expect it to work reasonably well... that being said IDEALLY ya want to rebias each time you retube an output... since someone already used an auto analogy let's stay with that... bias is like setting the idle...if it's too cold the amp doesnt respond quickly... if it's too hot they tend to burn up quickly... what you are doing is introducing a negative voltage at the tubes input to litterally shut it down... with out it the amp thermals... incedently dont think that you can just test one tube and get away with it ya really gotta do them both...
if you've been lucky so far good for you... i can remember working with a guy that insisted on doing something i told him would make it unstable... wouldnt beleive untill we had to do the last 1 1/2 set as a trio... btw ask the big guys if they rebias.... i did some soldanos for VAI once.... YMMV
