#1
Long story short. I had a set of 6L6. One broke. Bought another set. One broke. Now i have 2 broken tubes and 2 working tubes of different brands.

What kind of tester do I need to see if their current/ma/voltage/whatever the hell it is they have, is close enough to use together? Also how close does it need to be? is it in mA?

thanks
Quote by 311ZOSOVHJH
Congrats dude. I kinda want a BJ too 'cause I like them so much. I'll check your clipz later.

#2
I don't think this is something I could walk you through over the internet. Generally, it is not advised to put 2 different power tubes in an amp that were not shipped as a match pair.

(also, I'm liable to say something that is completely inaccurate as I'm not an amp tech)

As far as milliAmp variance - that depends on what amp you have but generally speaking you are safe up to say +/- 4 milliAmps. You will also need to find out what the appropriate plate voltage should be. If your amp doesn't have external trip pots you'll need to find out where the pots are inside the chassis so you can make your adjustments.

If this is the case, you also need to know what a filter cap is, how it can kill you, and how to drain them if necessary. NEVER put two hands inside an amp at once. In order to bias an amp manually like this you have open up the chassis and do this work WHILE THE AMP IS ON.

If you want to tackle this yourself, you'll need to do some research, get some help, scour youtube, etc. You'll need at a minimum a $30 octal tube biasing probe and a multimeter (voltmeter). The Weber Bias Rite is the way to go because it reduces the steps necessary and some of the guess work but it is $120.

That is all I have on this matter and yes I've done this.
#3
just bring it to a tech,save yourself from being electrocuted
Quote by angusfan16
I got my sister pregnant once. Yeah, that was awkward, but mostly because she's 6 years younger than me.
#4
Quote by 311ZOSOVHJH
I don't think this is something I could walk you through over the internet. Generally, it is not advised to put 2 different power tubes in an amp that were not shipped as a match pair.

(also, I'm liable to say something that is completely inaccurate as I'm not an amp tech)

As far as milliAmp variance - that depends on what amp you have but generally speaking you are safe up to say +/- 4 milliAmps. You will also need to find out what the appropriate plate voltage should be. If your amp doesn't have external trip pots you'll need to find out where the pots are inside the chassis so you can make your adjustments.

If this is the case, you also need to know what a filter cap is, how it can kill you, and how to drain them if necessary. NEVER put two hands inside an amp at once. In order to bias an amp manually like this you have open up the chassis and do this work WHILE THE AMP IS ON.

If you want to tackle this yourself, you'll need to do some research, get some help, scour youtube, etc. You'll need at a minimum a $30 octal tube biasing probe and a multimeter (voltmeter). The Weber Bias Rite is the way to go because it reduces the steps necessary and some of the guess work but it is $120.

That is all I have on this matter and yes I've done this.



I don't want to bias my amp. It's fixed bias and it should stay that way. whether its running them too hot or too cold i dont care less, in my experience i've always been fine with fixed bias amps and not biasing them. I think its unnecessary unless its a very bad bias set.

I just normally plug in matched tubes and play and it always works great.


All I want to do is make sure these tubes CAN be close enough in mA to be used as a matched pair. I dont know how to measure them.
Quote by 311ZOSOVHJH
Congrats dude. I kinda want a BJ too 'cause I like them so much. I'll check your clipz later.

#6
Quote by acdcrocks0323
Fixed bias means that the you have to bias your amp. Cathode bias means the amp adjusts itself to the tubes. Fixed bias is a very misleading term.


^exactly


injected, if you get a bias probe from say Eurotubes you can read the milliAmps if you have a multimeter. Whether or not these tubes of yours are close enough and 'matched' is another story that I can't answer. I was just trying to give you some tips to minimize damage to your amp and yourself.
#7
Well whatever you call it, the amp has no trim pots and im not going to install the parts needed to manually bias it. I just want to measure the tubes current/mA or whatever to see if i can use them together.

Quote by 311ZOSOVHJH
^exactly


injected, if you get a bias probe from say Eurotubes you can read the milliAmps if you have a multimeter. Whether or not these tubes of yours are close enough and 'matched' is another story that I can't answer. I was just trying to give you some tips to minimize damage to your amp and yourself.



I'm not trying to do anything to my amp... just the TUBES. i want to see if they rate close enough to be used together. i've installed a volume mod on my amp before, im no stranger to the insides of the amp and i know how to discharge the caps anyway. But im not going to install a bias mod.. thats not my goal.
Quote by 311ZOSOVHJH
Congrats dude. I kinda want a BJ too 'cause I like them so much. I'll check your clipz later.

Last edited by injected at Nov 25, 2009,
#8
Quote by injected
I don't want to bias my amp. It's fixed bias and it should stay that way. whether its running them too hot or too cold i dont care less, in my experience i've always been fine with fixed bias amps and not biasing them. I think its unnecessary unless its a very bad bias set.

I just normally plug in matched tubes and play and it always works great.


All I want to do is make sure these tubes CAN be close enough in mA to be used as a matched pair. I dont know how to measure them.
You see, this is just the problem, because you don't know how much current a certain tube is going to draw, if your amp is biased hot (without your knowledge) for the previous set of tubes and you install a set of tubes that draw even more plate current, you're ****ed, those tubes will be smoked very quickly.

The entire point of biasing an amp is to set the tube to an optimum plate current so that they safely perform, it's not just a matter of how a hot or cold bias sounds, that isn't the point, so it is in fact... VERY necessary. Fixed bias does not mean that it's not supposed to be adjusted. It means your bias (which is a negative voltage that directly affects the plate current) is set at a fixed value while the amp is in operation. That is all that it means.

You measure the current draw of a tube by... well... measuring the current draw under certain operating conditions. Tubes that draw a similar amount of plate current will be put together as "matched." If your amp is not set up to be biased and doesn't have a 1 ohm cathode to ground resistor, then you can't measure this in your amp unless you install one. Or you can use the Eurotubes bias probe like 311 suggested.
Last edited by al112987 at Nov 25, 2009,
#9
Quote by al112987
You see, this is just the problem, because you don't know how much current a certain tube is going to draw, if your amp is biased hot (without your knowledge) for the previous set of tubes and you install a set of tubes that draw even more plate current, you're ****ed, those tubes will be smoked very quickly.

The entire point of biasing an amp is to set the tube to an optimum plate current so that they safely perform, it's not just a matter of how a hot or cold bias sounds, that isn't the point, so it is in fact... VERY necessary. Fixed bias does not mean that it's not supposed to be adjusted. It means your bias (which is a negative voltage that directly affects the plate current) is set at a fixed value while the amp is in operation. That is all that it means.

You measure the current draw of a tube by... well... measuring the current draw under certain operating conditions. Tubes that draw a similar amount of plate current will be put together as "matched."



I don't know how my amp is biased. All i know is that ive put many tubes in it and they've all worked fine. Only I know those are matched tubes, and i dont know if these are close enough in current draw to be put together. I dont know how to check. Isnt there some kind of instrument i can use, directly onto the tubes, instead of running everything through my amp??
Quote by 311ZOSOVHJH
Congrats dude. I kinda want a BJ too 'cause I like them so much. I'll check your clipz later.

#10
the most reliable way of doing this is with your amp, because when the tubes are used, they're going to be drawing current from your amp. Just take 311s advice and get the bias probe. they're very easy to use you just stick the tube on it and stick it in the socket and you can measure directly off the probe without ever having to pull the chassis.
Last edited by al112987 at Nov 25, 2009,
#11
Thats the problem theres not really a quick easy no tool way to check these kind of specs. When running matched sets many times you can get away with no bias adjust. But if your gonna try to stick tubes of different manufacturers with unknown specs in there your really asking for trouble. You may not care less if things are to hot or cold but your amp certainly will.
#13
im happy with the way my amp is biased

I've used both of these tubes in my amp before, only with their respective other half. Is it safe to use them if i am unsure? At high volumes?

If theyre not close enough in draw to be matched, what are the adverse effects of using them? Will i cause any sort of damage to my amp? What are the risks?

Quote by 311ZOSOVHJH
OK man. How was I to know that? I didn't get that impression from your OP so I tried to give you a starting point for going about this correctly.


+1 Andrew



Not trying to be rude or anything. It's just fyi . My amp doesnt have trim pots and the like, so directions on how to test with those was kind of not important to me, is all.

Quote by Tackleberry
Thats the problem theres not really a quick easy no tool way to check these kind of specs. When running matched sets many times you can get away with no bias adjust. But if your gonna try to stick tubes of different manufacturers with unknown specs in there your really asking for trouble. You may not care less if things are to hot or cold but your amp certainly will.



Really? I thought there was something that would do this. Both tubes came to me in boxes that had a number on them, like 25mA or something like that.


I am very confused now! How do they find this mA number? Do they stick them in an amp and find the current?


Let me put it this way----- Are you telling me, that if things are running too hot or too cold, its because my amp isnt biased? I don't see how that's a problem. TONS of amps have no adjustable bias and are replaced by TONS of respective matched tubes - and are just fine. That's not what I'm asking.

I'm asking something else. When tubes come matched, I think it means they use the same amount of current, or close enough, to eachother. When you put them in an amp, they work drawing the same current. But say one tube is 31mA and one is 25mA. What does this do??? This means they're not "matched" right??? So one tube would draw 31mA and the other tube would draw... 31mA... right? Which is NOT optimal? Which risks it blowing?

I think i understand, if this is correct. Someone please break it down for me. I dont want to adjust the bias on my amp becuase id need to install the mod and its not necessary..
Quote by 311ZOSOVHJH
Congrats dude. I kinda want a BJ too 'cause I like them so much. I'll check your clipz later.

Last edited by injected at Nov 25, 2009,
#14
You don't need trim pots to test. You don't need to bias to test. You need a way to measure plate current which you measure at the tube. This has nothing to do with biasing because you're not going to be able to change the plate current anyway, but you can still measure it and compare the draw of the two tubes. That's how you determine if they are matched or not.
Quote by injected

I am very confused now! How do they find this mA number? Do they stick them in an amp and find the current?
That is precisely what they do, not necessarily on an amp, but on some regulated, power supply where the tube can at least approximate how it's going to behave in an amplifier, which is why you typically buy from reputable tube dealers who test this in advance when they send you matched tubes.
Last edited by al112987 at Nov 25, 2009,
#15
So I need to put the tubes in, turn the amp on standby(so theres current going to the power tubes but its not on) and measure their current draw? How do I do that? Like i said its a non adjustable bias amp.

Also this (again)...

I've used both of these tubes in my amp before, only with their respective other half.

Is it unsafe to use them if they are not matched?

If they are safe, what about at high volumes?

If theyre not close enough in draw to be matched, what are the adverse effects of using them?

Will i cause any sort of damage to my amp?

What are the risks?
Quote by 311ZOSOVHJH
Congrats dude. I kinda want a BJ too 'cause I like them so much. I'll check your clipz later.

#16
Quote by injected
So I need to put the tubes in, turn the amp on standby(so theres current going to the power tubes but its not on) and measure their current draw? How do I do that? Like i said its a non adjustable bias amp.
You don't need to adjust the bias. You're not adjusting ANYTHING, whether it's adjustable bias or not doesn't matter. You're just measuring something. And if you have the amp on standby, the high voltage B+ which supplies the juice for the tubes is not running, the tubes are only going to be drawing heater current. So you need to have the amp on and running.

That being said, I know you said you're not a stranger to the inside of an amp, but it really looks like you don't know much about how an amp actually works, and as a result, so I'm not going to recommend you do this. Installing a volume mod on an amp that is off and discharged is not the same as working on an amp that is up and running. There is some basic know how that is simple and easy, but is essential for safety, because the amp will kill your ass. But here it goes...

1) 311's advice on the bias probe is the easiest and safest method. I suggest it.

2) If you don't want to go with that, then pull the chassis and discharge filter caps.
3) check to see if there is a 1 ohm resistor from cathode of each tube to ground (doubtful, but check anyway)
4) If not, and making sure the amp has been discharged. Install a 1 ohm resistor where the cathode is tied to ground.
5) Install the tubes, turn on the amp, make sure you have a load connected, etc. etc.
6) Use a multimeter and measure voltage across the 1 ohm resistor. That will give you cathode current that you need. And measure for both tubes.

Again, this is dangerous because you will be working inside the amp while all the high voltage is present.
Last edited by al112987 at Nov 25, 2009,
#17
okay, well thats alot of steps.


Hypothetically, if these tubes were, lets say, 10mA apart and i put them in, what would happen if i cranked it and used the amp like normal?

Or more importantly, if one is 6L6GC and one is 6L6B... theyre different bottle shapes...
Quote by 311ZOSOVHJH
Congrats dude. I kinda want a BJ too 'cause I like them so much. I'll check your clipz later.

Last edited by injected at Nov 25, 2009,
#18
If your tubes are too far apart you'll magnetize your transformer and get some nasty hum and buzz, and the distortion will sound funny. It won't ruin your amp or anything.

Two different tube types is probably not something you want to get into unless you really know what you're doing.

As far as testing the match of the tubes, it's not really something you're going to be able to do yourself. You'd need a good tube tester to do that, and those tend to be expensive and hard to find, and very much not worth the price unless you're selling tubes.
#19
magnetize? That sounds dangerous! But if it wont ruin it, its ok to give it a shot then. If it sounds good and normal then i guess i can use them as TEMPORARIES..

And theyre not "different" tubes in the normal sense. Its not like im mixing an EL34 with a 6L6. They're both 6L6, just one is GC and one is B.

To my knowledge, they're the SAME tube, just different bottle shape??
Quote by 311ZOSOVHJH
Congrats dude. I kinda want a BJ too 'cause I like them so much. I'll check your clipz later.

#20
Quote by injected
okay, well thats alot of steps.


Hypothetically, if these tubes were, lets say, 10mA apart and i put them in, what would happen if i cranked it and used the amp like normal?

Or more importantly, if one is 6L6GC and one is 6L6B... theyre different bottle shapes...

I think you are asking for trouble and no offense was taken earlier - just trying to understand what you want to do.

What amp is this BTW?

When I biased my splawn I had to get these specs and such as you are asking about now. I was not going to use anything with a mA variance of greater than 4. I measured all 4 tubes and ended up selecting 2 (as I was pulling two tubes to reduce wattage) which matched the closest, one of which was 27mA and the other was 31mA.

My plate voltage was 470 which was within spec provided by manufacturer.


..
#21
Not asking for trouble, but if the only risk I take is "BAD SOUND" as compared to "AMP EXPLODING" then I'm fine with giving it a shot.

It's a Mesa DC-5 combo.

Not sure what Plate voltage is, or how it affects the mA.


Again though, so my amp should work fine with 2 6l6 tubes that dont match, but they might sound funny.

But what if one of them is a 6L6GC and one is a 6L6B, does this change things? will my amp have real risk for getting damaged??
Quote by 311ZOSOVHJH
Congrats dude. I kinda want a BJ too 'cause I like them so much. I'll check your clipz later.

Last edited by injected at Nov 25, 2009,
#22
6l6B and 6l6GC are not the same tube. Similar, but they're not always interchangeable. You can always use a GC where you could use a B, but you can't always replace a GC with a B.


The 6l6B is a 25 watt tube, and will handle 400V on the plates. The 6l6GC is a 30W and will handle a bit more, usually 500. If the amp originally had GCs you don't want to put a B in there. If it had a pair of 6l6Bs, you can put the GC in temporarily and the amp should work ok.
#23
Thats a little confusing. I have no idea what the amp had when it came stock from the factory. I know for a FACT that the 6L6B pair worked in the amp, and the 6L6GC pair worked in the amp too. So I should be ok then...?

Does it matter the order I put the tubes in? For example, if I put the GC in the first socket and the B in the second, both would be running at 500v to accomodate the GC tube?

Vice versa, would it be better to put the B in the first socket and the GC in the second, so both would be running at 400v?


I may be mis-reading this though. I could also think that the plate voltage in the amp is fixed; NOT changeable, so it wouldnt matter the order of the tubes, it would run at the same voltage for both no matter the order?


to cut the crap and get to the point- I know 6L6B tubes worked in this amp because i was using them before. Is it ok then, to use the working 6L6B and the working 6L6GC tube together, and it does NOT matter the order, and I would not ruin my amp at all, only if they draw different current it may sound bad?
Quote by 311ZOSOVHJH
Congrats dude. I kinda want a BJ too 'cause I like them so much. I'll check your clipz later.

Last edited by injected at Nov 25, 2009,
#24
Hey its your amp. But thats not very logical thinking that since 2 Bs worked in it and 2GCs worked in it that a mix would to. I guess at this point you can do whatever and let us know how it works.

The big distributors have tube testers for getting these specs and for matching. They test em then pair/quad em up.

In the old days you could go to a hardware store and they had testers looked sort of like a pinball machine with sockets for the various types of tubes available and little cubby holes stocked with replacement tubes. Of course this was when tubes were used in virtually everything. A quick google found a vintage tester for 300$, smaller one looked like a suitcase.

The same google found tube depot saying they match tubes to within 5% or 1ma.

Found this:
Mismatched tubes may increase desirable second harmonic distortion, though at the expensive of increased 60-cycle hum. (I've heard some people describe mismatched tubes as sounding "fatter.") Also, in theory a large enough mismatch could damage the output transformer, though it probably won't happen. It's safe to say that tubes drawing within 8mA of each other should be fine. Anything greater could cause long term damage.

Problem is you still need to know the mA and as someone else posted mixing types of tubes probably isnt the best idea. The 35 or so dollars spent on a new set of tubes is well worth less headaches.
Last edited by Tackleberry at Nov 25, 2009,
#25
I don't really know anything about this topic that hasn't already been said, better than I could. However, I can't help but notice that you have repeated the same questions the whole time no matter what people tell you. You are clearly just looking to validate what you already assume to be true, and you are ignoring people telling you otherwise. If you are so convinced that it'll be fine, despite what people tell you, then just do it.

So many times people come on here for validation, not information. I'm sorry, but you won't always hear what you want to.
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Unless its electronic drums.

BURN THE WITCH!!!!!
#26
^thank you tubetime - that is my observation as well


Quote by injected

to cut the crap and get to the point-


What do you mean 'cut the crap'?

What I read from that statement (and all of your other posts in this thread) is that for some reason you feel like we are just giving you the run-around and blowing smoke. I don't think anyone on this board wants to be responsible for something happening to your amp by saying 'yes injected, you can just pop whatever in there' - which seems to be the only answer you want to hear.

al122987 is very knowledgeable and Roc8995 IS an amp tech and I've personally done the things I outlined so it is possible we know what we are talking about.

If Roc says 6L6GC and 6L6B are different tubes that makes perfect sense to me. My guess is you had 2- GCs and 2 - Bs running in pairs before but that doesn't mean 1 from each set will work well together as a pair.

You said you got this back from the factory this way...you mean Mesa? Why don't you try contacting them or post on the boogie boards

The cost of a new matched set is worth it me thinks for a DC-5. I'd contact Doug at dougstubes if you want a second opinion on all of this.

Sorry if we didn't tell you want to hear
#27
?

It's not that im not liking what im hearing, it's just that I like to get 100% to the bottom of things. I mean "to cut the crap" by saying I'm talking my ass off way too much in trying to find exact things, and then I just summed up what I wanted to know.

I'm not ignoring Roc either - he told me if the amp worked with 6L6B's before, one could be replaced with a GC. So I said alright, it did work with 6L6B's so i'd be OK to do it then?

I don't really know anything about this topic that hasn't already been said, better than I could. However, I can't help but notice that you have repeated the same questions the whole time no matter what people tell you. You are clearly just looking to validate what you already assume to be true, and you are ignoring people telling you otherwise. If you are so convinced that it'll be fine, despite what people tell you, then just do it.

I'm just very precautious is all. If I was so sure, then I'd just do it no question. But I'm not. The only thing is I'm not getting the answers to my questions, but rather, "almost answers", that tell me some of what I want to know then something else that I don't really understand...


If Roc says 6L6GC and 6L6B are different tubes that makes perfect sense to me. My guess is you had 2- GCs and 2 - Bs running in pairs before but that doesn't mean 1 from each set will work well together as a pair.

Well exactly - but he also said if the B's worked in the amp before, one could be replaced with a GC.

I'm not trying to come off like I know everything because believe me I don't, but I'm very nervous about doing things where it could potentially damage my amp. But if the worse that's possible is bad sound, then im fine with taking that risk... who knows? maybe theyll be close in mA anyway.
Quote by 311ZOSOVHJH
Congrats dude. I kinda want a BJ too 'cause I like them so much. I'll check your clipz later.

#28
Quote by injected
?

It's not that im not liking what im hearing, it's just that I like to get 100% to the bottom of things. I mean "to cut the crap" by saying I'm talking my ass off way too much in trying to find exact things, and then I just summed up what I wanted to know.

I'm not ignoring Roc either - he told me if the amp worked with 6L6B's before, one could be replaced with a GC. So I said alright, it did work with 6L6B's so i'd be OK to do it then?

I don't really know anything about this topic that hasn't already been said, better than I could. However, I can't help but notice that you have repeated the same questions the whole time no matter what people tell you. You are clearly just looking to validate what you already assume to be true, and you are ignoring people telling you otherwise. If you are so convinced that it'll be fine, despite what people tell you, then just do it.

I'm just very precautious is all. If I was so sure, then I'd just do it no question. But I'm not. The only thing is I'm not getting the answers to my questions, but rather, "almost answers", that tell me some of what I want to know then something else that I don't really understand...


If Roc says 6L6GC and 6L6B are different tubes that makes perfect sense to me. My guess is you had 2- GCs and 2 - Bs running in pairs before but that doesn't mean 1 from each set will work well together as a pair.

Well exactly - but he also said if the B's worked in the amp before, one could be replaced with a GC.

I'm not trying to come off like I know everything because believe me I don't, but I'm very nervous about doing things where it could potentially damage my amp. But if the worse that's possible is bad sound, then im fine with taking that risk... who knows? maybe theyll be close in mA anyway.

Roc did not say that you can use a 6l6B and a 6l6GC where you previously used 6l6Bs... This is the exact problem, you are trying to take complex answers and boil them down to simple yes and nos. If you don't understand this stuff then maybe you shouldn't be messing with it.

I understand that you are frustrated that you aren't getting direct, simple answers, but there's a reason for that; tube amps are complex. If you don't understand how the WHOLE thing works then you can't understand how one little aspect of it works.
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Quote by Raijouta
Unless its electronic drums.

BURN THE WITCH!!!!!
#29
To answer the question about voltage:
The amp puts out a certain amount of voltage to the plates, so that is not dependent on the type of tube you put in it. So putting a GC in place of a B will not increase the plate voltage to 500, it will still be what it was before. So, if both types of tube are ok for that amp, you can replace the B with a GC.

Again, it's not a good long-term or high-volume solution, but if you need to practice for a couple weeks before you can get a matched pair of tubes, it's not going to blow up your amp unless there was something already wrong.


Although, here's a question I should have asked right away - you said that one tube in each pair broke - how did they break, and in what amp? If you just have butterfingers and dropped them, that's one thing, but if your amp is consistently killing one of the power tubes it needs to be looked at.
#30
Thank you, for the info.

The tubes broke due to carelessness. I was an idiot and smashed a cable into them while putting them in the back of the amp. Second times the charm...? I guess I've learned my lesson!
Quote by 311ZOSOVHJH
Congrats dude. I kinda want a BJ too 'cause I like them so much. I'll check your clipz later.