Tube Bias ????????
- Thread starter sweet_lou
- Start date
Curly
Moe's Bluesman
Re: Tube Bias ????????
from Weber's site:
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The following instructions are included with all Bias Rite current monitors:
Remove the output tubes and install the Bias Rite adapters. Install the output tubes in the Bias Rite adapter sockets. Allow the amp to warm up and turn the volume controls to zero. Select the output tube you want to adjust by selecting either A or B on the Bias Rite control panel. Adjust the G1 control for that tube and observe the panel meter for the correct current reading. In amplifiers that have only one bias control, alternate between A and B on the control panel and adjust for the best balance between the output tubes. With four output tubes, switch between A, B, C, and D to check the cathode current and/or proper balance. If you purchased the Bias Rite head only, set your voltmeter to read the lowest volts range. Then, the meter will read directly in milliamps. For instance, when your meter reads 35 millivolts (.035 volts), it is indicating 35 milliamps of cathode current.
We feel this is adequate for the amp technician or user who is familar with tubes and their operation with regards to understanding biasing, plate dissipation, etc. However, we have had a suggestion that our instructions aren't comprehensive enough for allowing a person to use the bias rite properly. The suggestion was to include tube data, expected current readings for various amps and tubes, etc. We, of course, cannot provide that kind of data due to the wide range of applications, plate voltages, cold-to-hot bias preference, etc. Therefore, if you decide to purchase a bias rite product, please familiarize yourself with tubes, maximum power dissipation ratings, how to read plate voltage and calculate plate power dissipation, and the general operation of power output circuits. Also visit the various technical bulletin boards on the internet to get more information on the subject.
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you might also check Aiken amps site - I think they have some info on biasing
then there's Ampage
Weber has several versions - I have a different brand, and my bias probe reads directly in Milliamps, so I just insert it into the socket with the tube attached, and take a reading
mine also had a chart with different tube specs, although I can never find it when I need to - but, you need the specs for your tube to know your bias range
from Weber's site:
------------
The following instructions are included with all Bias Rite current monitors:
Remove the output tubes and install the Bias Rite adapters. Install the output tubes in the Bias Rite adapter sockets. Allow the amp to warm up and turn the volume controls to zero. Select the output tube you want to adjust by selecting either A or B on the Bias Rite control panel. Adjust the G1 control for that tube and observe the panel meter for the correct current reading. In amplifiers that have only one bias control, alternate between A and B on the control panel and adjust for the best balance between the output tubes. With four output tubes, switch between A, B, C, and D to check the cathode current and/or proper balance. If you purchased the Bias Rite head only, set your voltmeter to read the lowest volts range. Then, the meter will read directly in milliamps. For instance, when your meter reads 35 millivolts (.035 volts), it is indicating 35 milliamps of cathode current.
We feel this is adequate for the amp technician or user who is familar with tubes and their operation with regards to understanding biasing, plate dissipation, etc. However, we have had a suggestion that our instructions aren't comprehensive enough for allowing a person to use the bias rite properly. The suggestion was to include tube data, expected current readings for various amps and tubes, etc. We, of course, cannot provide that kind of data due to the wide range of applications, plate voltages, cold-to-hot bias preference, etc. Therefore, if you decide to purchase a bias rite product, please familiarize yourself with tubes, maximum power dissipation ratings, how to read plate voltage and calculate plate power dissipation, and the general operation of power output circuits. Also visit the various technical bulletin boards on the internet to get more information on the subject.
------------------------------
you might also check Aiken amps site - I think they have some info on biasing
then there's Ampage
Weber has several versions - I have a different brand, and my bias probe reads directly in Milliamps, so I just insert it into the socket with the tube attached, and take a reading
mine also had a chart with different tube specs, although I can never find it when I need to - but, you need the specs for your tube to know your bias range
Re: Tube Bias ????????
Warm the amp up with the bias rite in one of the slots. turn all volumes down completely, then switch it from standy to play mode. What you read is what it is.
6L6's generally are in the 30-35 mA range.
I always go check KCA NOS Tubes site. Just click on hte power tube you are using and he'll list a range. Bias to ear.
Warm the amp up with the bias rite in one of the slots. turn all volumes down completely, then switch it from standy to play mode. What you read is what it is.
6L6's generally are in the 30-35 mA range.
I always go check KCA NOS Tubes site. Just click on hte power tube you are using and he'll list a range. Bias to ear.
aleclee
Major General GAS
Re: Tube Bias ????????
The advice of an amp tech I trust was as follows:
It's kind of like the way I set neck relief and action. Though I use some nominal values as a starting point (especially for neck relief), I'm not done 'til I play the guitar and make sure it's comfy and buzz-free.
The advice of an amp tech I trust was as follows:
- Start with the bias as cold as possible
- Increase the bias and play the amp a bit. It'll probably sound better as you go.
- At some point, it'll stop sounding better. It might not sound worse but the tone will stop improving.
- Check the bias to ensure you're not running too hot.
It's kind of like the way I set neck relief and action. Though I use some nominal values as a starting point (especially for neck relief), I'm not done 'til I play the guitar and make sure it's comfy and buzz-free.
Last edited:
Gearjoneser
Gear Ho
Re: Tube Bias ????????
Yep, keep your eye on the meter to make sure you don't go above 35mA.
It's just like adjusting the idle on a car....you know when the engine's running it's strongest. As soon as the amp sounds as loud and punchy as possible, that's where the bias should be set. Past that, and the amp starts to sound pushed or muddy.
I do it with the amp chassis' transformers resting on books, so the tubes have room to hang, and have the guitar and speaker cab plugged in. With one hand, I strum the A&D, while delicately adjusting the minipot with my right hand. The most important thing is to NOT let your hands touch anything, while inside a live chassis!!!!!
One wrong move with your hands next to exposed circuitry, and you could end up looking like a fryer chicken, dead on the floor. Careful!
Yep, keep your eye on the meter to make sure you don't go above 35mA.
It's just like adjusting the idle on a car....you know when the engine's running it's strongest. As soon as the amp sounds as loud and punchy as possible, that's where the bias should be set. Past that, and the amp starts to sound pushed or muddy.
I do it with the amp chassis' transformers resting on books, so the tubes have room to hang, and have the guitar and speaker cab plugged in. With one hand, I strum the A&D, while delicately adjusting the minipot with my right hand. The most important thing is to NOT let your hands touch anything, while inside a live chassis!!!!!
One wrong move with your hands next to exposed circuitry, and you could end up looking like a fryer chicken, dead on the floor. Careful!