New Member... New Amp!
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TwinACStacks
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Welcome to the forum Androo, and to the world of Marshall. Great Amps. I hear the MA series benefit greatly from a tube change as well. Send us some clips and give us a review. TWIN
Androo
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Any suggestions on which tubes to change and with what? I'm kind of concerned with the boosted overdrive since it sounds a tad cheap but I'm blaming it on the shitty speakers that I've got. I'm using a Fender FM212R combo amp which I modded to make it a 'cab'.
TwinACStacks
Well-Known Member
Greenbacks pretty much are the Standard. At least they would be my starting point on the speakers. You wouldn't go wrong with Tungsol 12AX7s in the Preamp with the exception of the cathode follower Tube, (usually V3 in a 4 tube preamp section or V2 in a 3 tube), as they have been known to fail from the higher voltage in this stage. Use an EH12AX7 here, and Winged "C" EL 34's.Just a suggestion.
TWIN
Androo
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Just a suggestion.
Erm... honestly, thanks for the advice I'm sure it is very good but I'm a bloody noob on tubes. Can you please explain to me more what I sould buy (exact model number) etc... Please!
Sorry for my ignorance but that's the reason I joined... to get to know tubes and whatnot. Thanks!
EDIT: Is this what you're talking about: Tungsol 12AX7s on eBay.
So I should get 3 of these? What about bias? Actually... what the hell is bias? I read it in another thread and just can't get to comprehend it.
Help.
TwinACStacks
Well-Known Member
That's probably it, I'm leary of Evilbay:Tung-Sol 12AX7 X2
Electro-Harmonix 12AX7-EH X1
Winged "C" (SED) EL34 X4 Matched Quad.
You don't have to rebias if you only change the pre amp tubes. If you change the Power tubes Yes.
TWIN
Androo
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Tung-Sol 12AX7 X2
Electro-Harmonix 12AX7-EH X1
Winged "C" (SED) EL34 X4 Matched Quad.
You don't have to rebias if you only change the pre amp tubes. If you change the Power tubes Yes.
I'm from Malta [Europe] so buying from online US stores is a major problem for me, which is why I went for eBay. The link I posted was from a power seller so I guess I could trust him/her.
By the way, you're of the opinion that I should change all 5 tubes?
TwinACStacks
Well-Known Member
Androo here is a Non-technical explaination of bias:
No matter how good the amp design or manufacture, tubes wear out. That's why you have to replace them. They are similar to light bulbs in that respect. Now for the tech-talk...
Tube bias for guitar amplifiers?
It’s easy to understand tube bias without an electronic-engineering background.
Imagine that electrons are a bunch of energetic little guys, who run around when you put pressure on them. The pressure gives them energy, so they want to move. The pressure is called VOLTAGE. (Voltage is to electrons what Starbucks is to humans.) The number of electrons moving thru a wire per-second is called CURRENT.
Think of electronic current exactly as you would of a stream or river. Some streams are narrow, but flow down a steep incline. Gravity is akin to voltage in the sense that it provides the impetus to move downhill. If a stream is narrow, it has less “current” than a mighty river. Here, electrons are analogous to the number of water molecules. The big river could have much more potential energy, because it has more water, even if it flows down less-steep incline. Of course, you could have a BIG river that flows straight down, like Niagara Falls. That is a LOT of CURRENT!
In a vacuum tube, electrons emit from a hot thing called a CATHODE. They pop off the cathode and float around in the empty space around the cathode. They do this because the cathode is made of a material that emits electrons when it is heated.
Remember that electricity is like magnetism; it has a positive and a negative component. With electrons, as with magnets, opposites attract, while like-charges repel.
Since electrons all have a NEGATIVE charge they tend to REPEL each other. So a cloud of them in a tube tends to want to disperse OUTWARD. (“negative and positive” are both part of an arbitrary nomenclature standard that was established hundreds of years ago by Benjamin Franklin.)
Now we have the cathode with a cloud of electrons all jostling to get away from each other, but there isn't anyplace for them to go.
So there's another metal thing in the tube. It's called either a PLATE or an ANODE. Now, we put a POSITIVE charge on the plate.
The electrons, which are negative, are ATTRACTED to it, because of its OPPOSITE POSITIVE CHARGE.
Electrons pop out of the cathode and zip straight to the plate. They hit the plate, penetrate, and become moving electric current in a wire. This current can do useful things, like push a speaker-cone to make sound.
That is (basically) how any amplifier works.
OK, but are there a LOT of electrons moving through the tube? Yes, there are lots of them. So many that if we left this tube operating, it would destroy itself! The electrons hitting the plate cause it to heat up. If there are enough electrons heating it up, it will turn red-hot, melt the tube's glass envelope and the tube would die a dramatic death. (hissing, sparking and other dangerous fireworks.)
So, we apply a BIAS voltage to a grid (of little wires) that acts like a sieve. This is a steady NEGATIVE voltage, more negative than the cathode. Since like REPELS like, the negative voltage will REDUCE the number of electrons passing through the grid.
You can think of this bias voltage as a shutter or venetian blind on your window. You control how much light gets through by adjusting the blind. In a very real sense, this is exactly what we do with bias on the grid. It acts like a shutter to repel some of the electrons, just as a shutter repels photons... (light.)
We set this voltage so the current to the plate is a tolerable IDLE current. The current is determined by the tube's design and ability to handle it, plus by the circuit outside the tube. Each kind of tube has its own optimal operating point.
By making this bias voltage adjustable, we can set it as desired. However, only certain amplifiers have an adjustment for bias, and those that have bias adjustments usually don't make them accessible to the user.
Why?
With so many litigious lawyers around, manufacturers are understandably squeamish about letting unauthorized people play with deadly voltages.
I am NOT joking here! I have seen idiots get knocked down to the floor while diddling with amplifiers.
It is kind of funny in a Darwinian sense... maybe electricity is meant to weed out the weak.
However, if you like your musician "buddy" enough to buy him that expensive boutique amp, you probably don't want him to catch a jolt from the large capacitors in that tube amp while he has it open on a bench.
Professional technicians have strict procedures for evacuating capacitors and grounding the amp-chassis before they putz in the amp's guts.
I am not kidding at all. If you don't have the know-how, and you poke around inside an amplifier, even when it is off and unplugged, it can KILL!
THAT is why you pay a technician!
So why do you have to re-bias when you replace tubes?
You have to understand; tubes VARY from sample to sample. Applying a given bias voltage to a tube is OK, if it's adjusted the tube will idle properly (and work properly). But if you CHANGE your tube or tubes, how do you know they'll bias properly without adjusting the bias? The new tube might be different in bias requirement.
It would be GREAT if tubes were rated by their individual bias voltage. Actually most companies that sell "matched" tubes usually print the bias current the tube operates at, right on the box. Unfortunately, each company has their OWN STANDARDS for measuring bias. Plate voltages, plate currents, and other parameters are DIFFERENT from one dealer to another. So they may or MAY NOT be interchangeable.
BIAS POINT RATINGS split up the Gaussian distribution into a series of ZONES. This scheme is very similar to the 1-10 rating scheme used by one of the major sellers of pre-tested tubes. (I won’t mention the name, but the initials are “GT” and name rhymes with “move boobs.”)
Basically, that company says that tubes with a lower number on that 1-10 scale "BREAK UP SOONER" than usual. And tubes on the high end of the scale "BREAK UP LATER".
Even though their rating system is based on the individual bias variances of the tubes, the other company likes to claim their system is "secret" and "proprietary". That’s BS, …a marketing lie. Their "5" rated tubes are smack in the middle of the Gaussian bell curve. That's all it means!
The tubes that are on the LOW side of the bell curve are low BIAS POINT tubes. They are usually prone to "breaking up" or going into distortion at lower than the proper volume (for that kind of tube).
So they have LOWER HEADROOM. For some musical-instrument applications, the user may want this effect. (distortion mongering Rock-guitarists for instance)
That is undesirable for high-end audio, because lower idle current means higher distortion, which most people dislike hearing in their music playback.
Tubes in the MIDDLE zones fit the average profile for that tube type. They are most commonly recommended for the average amplifier user, especially for high-end audio amplifiers. These tubes will give the PROPER amount of headroom for their operating point. So the amplifier will perform as the manufacturer intended.
Tubes with a high BIAS POINT will idle at a higher current than specified, and give more headroom than the amplifier designer intended. With high BIAS POINT tubes, your amplifier volume / gain will need to be turned up much higher to achieve "break up". Some instrument amplifier users might wish for this sound effect. ( i.e. Jazz guitarists)
TWIN
No matter how good the amp design or manufacture, tubes wear out. That's why you have to replace them. They are similar to light bulbs in that respect. Now for the tech-talk...
Tube bias for guitar amplifiers?
It’s easy to understand tube bias without an electronic-engineering background.
Imagine that electrons are a bunch of energetic little guys, who run around when you put pressure on them. The pressure gives them energy, so they want to move. The pressure is called VOLTAGE. (Voltage is to electrons what Starbucks is to humans.) The number of electrons moving thru a wire per-second is called CURRENT.
Think of electronic current exactly as you would of a stream or river. Some streams are narrow, but flow down a steep incline. Gravity is akin to voltage in the sense that it provides the impetus to move downhill. If a stream is narrow, it has less “current” than a mighty river. Here, electrons are analogous to the number of water molecules. The big river could have much more potential energy, because it has more water, even if it flows down less-steep incline. Of course, you could have a BIG river that flows straight down, like Niagara Falls. That is a LOT of CURRENT!
In a vacuum tube, electrons emit from a hot thing called a CATHODE. They pop off the cathode and float around in the empty space around the cathode. They do this because the cathode is made of a material that emits electrons when it is heated.
Remember that electricity is like magnetism; it has a positive and a negative component. With electrons, as with magnets, opposites attract, while like-charges repel.
Since electrons all have a NEGATIVE charge they tend to REPEL each other. So a cloud of them in a tube tends to want to disperse OUTWARD. (“negative and positive” are both part of an arbitrary nomenclature standard that was established hundreds of years ago by Benjamin Franklin.)
Now we have the cathode with a cloud of electrons all jostling to get away from each other, but there isn't anyplace for them to go.
So there's another metal thing in the tube. It's called either a PLATE or an ANODE. Now, we put a POSITIVE charge on the plate.
The electrons, which are negative, are ATTRACTED to it, because of its OPPOSITE POSITIVE CHARGE.
Electrons pop out of the cathode and zip straight to the plate. They hit the plate, penetrate, and become moving electric current in a wire. This current can do useful things, like push a speaker-cone to make sound.
That is (basically) how any amplifier works.
OK, but are there a LOT of electrons moving through the tube? Yes, there are lots of them. So many that if we left this tube operating, it would destroy itself! The electrons hitting the plate cause it to heat up. If there are enough electrons heating it up, it will turn red-hot, melt the tube's glass envelope and the tube would die a dramatic death. (hissing, sparking and other dangerous fireworks.)
So, we apply a BIAS voltage to a grid (of little wires) that acts like a sieve. This is a steady NEGATIVE voltage, more negative than the cathode. Since like REPELS like, the negative voltage will REDUCE the number of electrons passing through the grid.
You can think of this bias voltage as a shutter or venetian blind on your window. You control how much light gets through by adjusting the blind. In a very real sense, this is exactly what we do with bias on the grid. It acts like a shutter to repel some of the electrons, just as a shutter repels photons... (light.)
We set this voltage so the current to the plate is a tolerable IDLE current. The current is determined by the tube's design and ability to handle it, plus by the circuit outside the tube. Each kind of tube has its own optimal operating point.
By making this bias voltage adjustable, we can set it as desired. However, only certain amplifiers have an adjustment for bias, and those that have bias adjustments usually don't make them accessible to the user.
Why?
With so many litigious lawyers around, manufacturers are understandably squeamish about letting unauthorized people play with deadly voltages.
I am NOT joking here! I have seen idiots get knocked down to the floor while diddling with amplifiers.
It is kind of funny in a Darwinian sense... maybe electricity is meant to weed out the weak.
However, if you like your musician "buddy" enough to buy him that expensive boutique amp, you probably don't want him to catch a jolt from the large capacitors in that tube amp while he has it open on a bench.
Professional technicians have strict procedures for evacuating capacitors and grounding the amp-chassis before they putz in the amp's guts.
I am not kidding at all. If you don't have the know-how, and you poke around inside an amplifier, even when it is off and unplugged, it can KILL!
THAT is why you pay a technician!
So why do you have to re-bias when you replace tubes?
You have to understand; tubes VARY from sample to sample. Applying a given bias voltage to a tube is OK, if it's adjusted the tube will idle properly (and work properly). But if you CHANGE your tube or tubes, how do you know they'll bias properly without adjusting the bias? The new tube might be different in bias requirement.
It would be GREAT if tubes were rated by their individual bias voltage. Actually most companies that sell "matched" tubes usually print the bias current the tube operates at, right on the box. Unfortunately, each company has their OWN STANDARDS for measuring bias. Plate voltages, plate currents, and other parameters are DIFFERENT from one dealer to another. So they may or MAY NOT be interchangeable.
BIAS POINT RATINGS split up the Gaussian distribution into a series of ZONES. This scheme is very similar to the 1-10 rating scheme used by one of the major sellers of pre-tested tubes. (I won’t mention the name, but the initials are “GT” and name rhymes with “move boobs.”)
Basically, that company says that tubes with a lower number on that 1-10 scale "BREAK UP SOONER" than usual. And tubes on the high end of the scale "BREAK UP LATER".
Even though their rating system is based on the individual bias variances of the tubes, the other company likes to claim their system is "secret" and "proprietary". That’s BS, …a marketing lie. Their "5" rated tubes are smack in the middle of the Gaussian bell curve. That's all it means!
The tubes that are on the LOW side of the bell curve are low BIAS POINT tubes. They are usually prone to "breaking up" or going into distortion at lower than the proper volume (for that kind of tube).
So they have LOWER HEADROOM. For some musical-instrument applications, the user may want this effect. (distortion mongering Rock-guitarists for instance)
That is undesirable for high-end audio, because lower idle current means higher distortion, which most people dislike hearing in their music playback.
Tubes in the MIDDLE zones fit the average profile for that tube type. They are most commonly recommended for the average amplifier user, especially for high-end audio amplifiers. These tubes will give the PROPER amount of headroom for their operating point. So the amplifier will perform as the manufacturer intended.
Tubes with a high BIAS POINT will idle at a higher current than specified, and give more headroom than the amplifier designer intended. With high BIAS POINT tubes, your amplifier volume / gain will need to be turned up much higher to achieve "break up". Some instrument amplifier users might wish for this sound effect. ( i.e. Jazz guitarists)
TWINlongfxukxnhair
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Welcome to the Forum and welcome to Marshall!
Androo
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TWIN.... thanks! So I should be looking into tubes with a middle Bias point? I have no idea what the bias of my amp is and since you said it can actually kill if I were to meddle with that stuff [even unplugged] I'm scared to even go near it!
Androo
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longfxukxnhair
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Thanks! I've got the Tobacco Burst Slash Sig like you dude.
Thats beautiful. Thats not the one I have. I have the one with the Fishman. Wjich is his second signature LP. I also have the Snake Pit and the Gold Top. I would love to get the Slash VOS.
longfxukxnhair
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Yours came out at the same time as the VOS in April 08. Correct? How do you like it plugged into your MA?
Androo
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I love it but I definitely need a great cab for it. A modded SS combo is not the way to go!
Plus a change of tubes supposedly removes the subtle fuzziness of the boosted overdrive! Will get to that in the future.
longfxukxnhair
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Dump the SS. Get a 1960 cab. Unleash that beast!
longfxukxnhair
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Dont worry about Twin. He is a good guy. He can answer a lot of your questions. He gets a little scared when he sees a amp with that many knobs. He then has to remove his shoes to count them when there are more than 10.
TwinACStacks
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There should be 7 tubes in that head if it's a 100 Watt if it's a 50 watt there will only be 5. The 3 small are the pre-amps, the 4 or 2 large are the power tubes. I have no Idea if your amp has bias test points or trim pots I can't seem to find a schematic for it. Best for You to take it to a local Tech and have him replace the tubes. Buy from Ebay, you should be safe with CP (current production) tubes as they usually don't counterfeit these. Get what I told You 2 Tungsol 12AX7's and One Electroharmonix 12AX7 for Your V2 cathode follower position and a Matched QUAD or PAIR (4 or 2) SED Winged "C" EL34's Take these and have Your Tech install them and Bias Your amp at about 65% Dissipation at idle. Also TELL him the Electroharmonix 12AX7 is for the Cathode Follower Position.
TWIN
Androo
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Just checked... that cab is more expensive then my amp! I'm actually looking for a 2x12 not a 4x12.
Are Crate cabs any good? Behringher or Laney? Maybe a Blackstar HT212....
longfxukxnhair
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Whats the cost of a 1936 2x12? No Crate or Behringher. Laney and Blackstar I have no exp with.
