Rookie bias question

[nix_gibby]

And why the volume should be on zero, or it doesn't matter actually?

 

[FourT6and2]

And why the volume should be on zero, or it doesn't matter actually?

Set the volume to zero.

Bias = the amp's setting when the tubes are idle. If there's any signal or sound going through your amp, your bias (idle current) won't be accurate. When you play through the amp or even if there is white noise going through your amp, your bias number won't be accurate. Unplug your instrument cable from the input and turn the volume to zero.

 

[nix_gibby]

Hey, thanks! That's what I call a goood explanation!

 

[Ventura]

Your probably don't want to hear this, but it might be a good idea to have a tech take the zap for you.

Concur - or invest in a BiasRite.

AND THERE'S THAT AVATAR I LOVE SO MUCH!!!!!

 

[FourT6and2]

Your probably don't want to hear this, but it might be a good idea to have a tech take the zap for you.

Concur - or invest in a BiasRite.

Nonsense. If you can plug in a USB cord to your laptop, you can bias your amp with external bias points.

And why would one need a BiasRite when their amp has external bias test points? Maybe if they need to measure their plate voltage and they're afraid to do that. But really, this stuff is so simple. It's like paying a tech to change your guitar's strings. Why would anybody do that? Might as well just throw money into a paper shredder.

 

[maddnotez]

Your probably don't want to hear this, but it might be a good idea to have a tech take the zap for you.

Concur - or invest in a BiasRite.

Nonsense. If you can plug in a USB cord to your laptop, you can bias your amp with external bias points.

And why would one need a BiasRite when their amp has external bias test points? Maybe if they need to measure their plate voltage and they're afraid to do that. But really, this stuff is so simple. It's like paying a tech to change your guitar's strings. Why would anybody do that? Might as well just throw money into a paper shredder.

Well not all amps have external points. Maybe OP's does idk but mine does not. Plus I hear external points are not as accurate. IDK if that is true or not but that is what I have heard.

 

[JamesPeters]

Well not all amps have external points. Maybe OP's does idk but mine does not. Plus I hear external points are not as accurate. IDK if that is true or not but that is what I have heard.

These are good points.

On the last point: depending on what the amp's bias points read (cathode current or bias voltage), and what components (usually just resistors) are used in that part of the circuit, it's possible a bias meter is more accurate. If the amp's test points measure the bias voltage (-ve voltage "injected" at the grid of the output tube to set its bias state), it's not a direct indicator what the current draw of the tube will be. It can also be confusing since test points for this sort of thing are often done "backwards" so a "higher number" means a voltage that's even lower (making for a "colder" bias setting, less current passes through the tube). So some people will bias "hotter" without realizing it, thinking it's a safer setting (believing a lower number to be "colder" or less current draw). With a number like "40v" to shoot for with such a test point, it further adds to the confusion since that's close to a number in mA for a single tube's current draw in an average guitar amp (or in mV depending on the test points or bias tester used). You can even ask a person multiple times "did you read the manufacturer's biasing instructions and follow them precisely?", and ask "what do they say for the test points?" and the person can still get something wrong.

So if your amps have bias test points and you know how they work/what they really measure, yeah why buy a bias meter. But on the flipside, having a bias meter is useful.

BTW I own one of Weber's older Biasrite models. It's still working after...15 years, I think? I only use it to bias other people's amps, not my own. The only problem it had (the new ones apparently don't where the wire harnesses enter the tube socket thingies made of copper, it didn't have strain reliefs, so the outer jacket for the wire harness broke (exposing the wires within). The inner wires have their own insulation, and the outer insulation that remains in the holes (since it's glued there) acts as a strain relief for that. So my bias meter still works properly despite that. I see in Weber's photos that now there are rubber gaskets of some kind to act as strain relief for this, so that's good.

About plate voltage: yes, it's helpful to know that. Notice I don't say "critical" though. Most guitar amps with 2 or 4 common octal-based output tubes are going to have plate voltage between 400V-500V. Usually it's somewhere in the middle, with some exceptions. The difference of 20V "give or take" between amps (and at different bias settings) isn't critical to consider as part of the calculation. Assuming something with plate voltage around 450V, do the calculation and then try it again for 470V. Your bias setting "to shoot for" will be 4% different (around 1.5mA difference). Given that the acceptable bias range for the output tube current is far greater than that, it doesn't tell you much about what setting to shoot for. You're still either going to adjust it by ear or with a scope (whatever method you use for your final confirmation.) If you're trying to walk a fine line with your bias before the plates start glowing, biasing as hot as possible...well you're still going to have to look at the tubes and listen to how it reacts at higher volumes (and this varies from output tube set to set anyway). So usually it's not important to measure plate voltage unless your amp is a bit unusual...and you might already realize that based on why you decided to buy the amp in the first place (for instance is it using 4x EL34 for 40W output or something like that...it's a strong hint you won't be biasing it the same, and hopefully the manufacturer explains about this). Another consideration: if the amp is only designed for certain tubes which are unusual, and no "compatibility" with EL34/6L6 is mentioned.

 

[FourT6and2]

Your probably don't want to hear this, but it might be a good idea to have a tech take the zap for you.

Concur - or invest in a BiasRite.

Nonsense. If you can plug in a USB cord to your laptop, you can bias your amp with external bias points.

And why would one need a BiasRite when their amp has external bias test points? Maybe if they need to measure their plate voltage and they're afraid to do that. But really, this stuff is so simple. It's like paying a tech to change your guitar's strings. Why would anybody do that? Might as well just throw money into a paper shredder.

Well not all amps have external points. Maybe OP's does idk but mine does not. Plus I hear external points are not as accurate. IDK if that is true or not but that is what I have heard.

Well this thread is about an amp with external bias points, so...

 

[FourT6and2]

Well not all amps have external points. Maybe OP's does idk but mine does not. Plus I hear external points are not as accurate. IDK if that is true or not but that is what I have heard.

These are good points.

On the last point: depending on what the amp's bias points read (cathode current or bias voltage), and what components (usually just resistors) are used in that part of the circuit, it's possible a bias meter is more accurate. If the amp's test points measure the bias voltage (-ve voltage "injected" at the grid of the output tube to set its bias state), it's not a direct indicator what the current draw of the tube will be. It can also be confusing since test points for this sort of thing are often done "backwards" so a "higher number" means a voltage that's even lower (making for a "colder" bias setting, less current passes through the tube). So some people will bias "hotter" without realizing it, thinking it's a safer setting (believing a lower number to be "colder" or less current draw). With a number like "40v" to shoot for with such a test point, it further adds to the confusion since that's close to a number in mA for a single tube's current draw in an average guitar amp (or in mV depending on the test points or bias tester used). You can even ask a person multiple times "did you read the manufacturer's biasing instructions and follow them precisely?", and ask "what do they say for the test points?" and the person can still get something wrong.

So if your amps have bias test points and you know how they work/what they really measure, yeah why buy a bias meter. But on the flipside, having a bias meter is useful.

BTW I own one of Weber's older Biasrite models. It's still working after...15 years, I think? I only use it to bias other people's amps, not my own. The only problem it had (the new ones apparently don't where the wire harnesses enter the tube socket thingies made of copper, it didn't have strain reliefs, so the outer jacket for the wire harness broke (exposing the wires within). The inner wires have their own insulation, and the outer insulation that remains in the holes (since it's glued there) acts as a strain relief for that. So my bias meter still works properly despite that. I see in Weber's photos that now there are rubber gaskets of some kind to act as strain relief for this, so that's good.

About plate voltage: yes, it's helpful to know that. Notice I don't say "critical" though. Most guitar amps with 2 or 4 common octal-based output tubes are going to have plate voltage between 400V-500V. Usually it's somewhere in the middle, with some exceptions. The difference of 20V "give or take" between amps (and at different bias settings) isn't critical to consider as part of the calculation. Assuming something with plate voltage around 450V, do the calculation and then try it again for 470V. Your bias setting "to shoot for" will be 4% different (around 1.5mA difference). Given that the acceptable bias range for the output tube current is far greater than that, it doesn't tell you much about what setting to shoot for. You're still either going to adjust it by ear or with a scope (whatever method you use for your final confirmation.) If you're trying to walk a fine line with your bias before the plates start glowing, biasing as hot as possible...well you're still going to have to look at the tubes and listen to how it reacts at higher volumes (and this varies from output tube set to set anyway). So usually it's not important to measure plate voltage unless your amp is a bit unusual...and you might already realize that based on why you decided to buy the amp in the first place (for instance is it using 4x EL34 for 40W output or something like that...it's a strong hint you won't be biasing it the same, and hopefully the manufacturer explains about this). Another consideration: if the amp is only designed for certain tubes which are unusual, and no "compatibility" with EL34/6L6 is mentioned.

I'm interested to know what the amps are you've come cross where the test points were wired backwards, in such a way where a higher mV reading = colder bias and a lower mV reading = hotter. Or are you referring to a situation where it's more a negative number thing. So -32mV is actually colder than -20mV? Versus it being a positive reading. In which case, you can simply reverse your multimeter plugs.

 

[PBGas]

The other important thing that a friend of mine recently found out the hard way is to make sure you know which tubes are paired when you are doing a bias check. I know a lot of amps are 2 outer and 2 inner as pairs but on the XTC, it's V7 V9 as pair and V8 and V10 as the other pair.

 

[JamesPeters]

I'm interested to know what the amps are you've come cross where the test points were wired backwards, in such a way where a higher mV reading = colder bias and a lower mV reading = hotter. Or are you referring to a situation where it's more a negative number thing. So -32mV is actually colder than -20mV? Versus it being a positive reading. In which case, you can simply reverse your multimeter plugs.

Peavey JSX. The test points measure bias voltage, and they were wired backwards so you don't read a negative voltage when you use them as Peavey describes. Then they provide a bias voltage to shoot for...and as I showed the owner of the amp, depending on the tubes the current draw varied over a significant range with that recommended bias voltage. The fact it's a bias voltage confused him (especially since they said to shoot for a positive number and not a negative one) and he was using the test points as though they were like on a Marshall he owned (or like on my amps for instance). He was confused because it just sounded terrible.

Anyway they probably did that with more of their amps.

 

[FourT6and2]

I'm interested to know what the amps are you've come cross where the test points were wired backwards, in such a way where a higher mV reading = colder bias and a lower mV reading = hotter. Or are you referring to a situation where it's more a negative number thing. So -32mV is actually colder than -20mV? Versus it being a positive reading. In which case, you can simply reverse your multimeter plugs.

Peavey JSX. The test points measure bias voltage, and they were wired backwards so you don't read a negative voltage when you use them as Peavey describes. Then they provide a bias voltage to shoot for...and as I showed the owner of the amp, depending on the tubes the current draw varied over a significant range with that recommended bias voltage. The fact it's a bias voltage confused him (especially since they said to shoot for a positive number and not a negative one) and he was using the test points as though they were like on a Marshall he owned (or like on my amps for instance). He was confused because it just sounded terrible.

Anyway they probably did that with more of their amps.

Interesting. Was it a mistake on Peavey's part or they're all wired like that?

 

[JamesPeters]

It's intentional as far as I can tell, and on all of them. That's the least of that amp's problems though.

 

[gtrplr71]

I have a question about Biasing. I have a fieldpiece MM witch setting should it be on to read the bias? there is a VAC setting 200 and 600. there is a VDC 20 setting there is a VAC 600 and 200 setting, MFD setting and an ADC setting.

 

[JamesPeters]

I have a question about Biasing. I have a fieldpiece MM witch setting should it be on to read the bias? there is a VAC setting 200 and 600. there is a VDC 20 setting there is a VAC 600 and 200 setting, MFD setting and an ADC setting.

What method are you using for biasing? Are you connecting something like the Weber Bias Rite "head" to it? Does your amp have bias test points and if so what do they measure?

 

[gtrplr71]

I have a question about Biasing. I have a fieldpiece MM witch setting should it be on to read the bias? there is a VAC setting 200 and 600. there is a VDC 20 setting there is a VAC 600 and 200 setting, MFD setting and an ADC setting.

What method are you using for biasing? Are you connecting something like the Weber Bias Rite "head" to it? Does your amp have bias test points and if so what do they measure?

I have Bias ports on the back of my ceriatone son of yeti head. Measure in mV. I just cant get a reading on the multi meter except in the continuity mode. here is a link to the picture I took
https://s1030.photobucket.com/user/Gtrpl ... ml?filters[user]=144663744&filters[recent]=1&sort=1&o=0

 

[JamesPeters]

I'm not familiar with that amplifier so I don't know exactly what that is supposed to measure and I don't want to assume anything. What is it measuring, and what does the manufacturer say about it?

 

[gtrplr71]

It is a 20 watt 6v6 Plexi head with the Jose Mod. the bias should be set at 24 mA but I just don't know what mode the Multi meter should be in for it to read properly it is a new multi meter. nothing on the meter is marked to read mA clearly.

 

[FourT6and2]

You need to set your meter to millivolts DC. If your meter doesn't have that setting then you're out of luck.

 

[gtrplr71]

No it does not clearly say DC mV on the dial of the meter there is a VAC setting 200 and 600. there is a VDC 20 setting there is a VAC 600 are on the meter dial.