bigmack209
New member
And do i need it?
/flameshield
/flameshield
What is tube biasing?
- Thread starter bigmack209
- Start date
misterwhizzy
Well-known member
Re: What is tube biasing?
Tube biasing is setting the amount of current that your power tubes draw at idle. Whether or not you need it depends on what type of amp you have and the topology of the power tubes. If it's fixed bias class A/B and not a Mesa, you probably need it.
Tube biasing is setting the amount of current that your power tubes draw at idle. Whether or not you need it depends on what type of amp you have and the topology of the power tubes. If it's fixed bias class A/B and not a Mesa, you probably need it.
TwilightOdyssey
Darkness on the edge of Tone
Re: What is tube biasing?
Some amplifiers require biasing, others do not. You can change your amp's tonal characteristics and response by changing the bias. Starting within the spec for the manufacturer for the power valves is the best place to start.
Do you NEED it?
Depends on who you ask, how far out of whack your power valves drift, and how often you like to replace them.
Some amplifiers require biasing, others do not. You can change your amp's tonal characteristics and response by changing the bias. Starting within the spec for the manufacturer for the power valves is the best place to start.
Do you NEED it?
Depends on who you ask, how far out of whack your power valves drift, and how often you like to replace them.
STRATDELUXER97
Stratoblaster Tone Meister
Re: What is tube biasing?
What specific amp are we talking about? Some are already cathode biased via preset resistances within the amp..Most amps aren't this way however.
What specific amp are we talking about? Some are already cathode biased via preset resistances within the amp..Most amps aren't this way however.
bigmack209
New member
Re: What is tube biasing?
Epiphone Galaxie 25, 4 12AX7s and 2 EL84s, All JJ Eurotubes
Epiphone Galaxie 25, 4 12AX7s and 2 EL84s, All JJ Eurotubes
Last edited:
Lazarus1140
New member
trevorus
Modsterbator
Re: What is tube biasing?
Looks like they even put a 10 turn pot in there! Don't see that too often!
Looks like they even put a 10 turn pot in there! Don't see that too often!
bigmack209
New member
Re: What is tube biasing?
what's a 10 turn pot?
so do i just walk in to my local music store and say "hey can you bias this please"?
lol... sorry, i'm pretty new to tubes.
also, it shows that 12AT7 with the reverb tank, does that mean that tube SHOULDN'T be a 12AX7? cus mine is... and my amp hums. a lot.
what's a 10 turn pot?
so do i just walk in to my local music store and say "hey can you bias this please"?
lol... sorry, i'm pretty new to tubes.
also, it shows that 12AT7 with the reverb tank, does that mean that tube SHOULDN'T be a 12AX7? cus mine is... and my amp hums. a lot.
trevorus
Modsterbator
Re: What is tube biasing?
A 12AX7 and a 12AT7 amplify differently, to put it in simple terms. It's best to go back to a 12AT7. Might help, might not, but at least the reverb will be running properly. A 10 turn pot is a potentiometer (like your guitar's volume control) that has a lot of turns, so there is a very fine level of accuracy. Taking your amp to a tech is probably a good idea, and have them bias it properly.
A 12AX7 and a 12AT7 amplify differently, to put it in simple terms. It's best to go back to a 12AT7. Might help, might not, but at least the reverb will be running properly. A 10 turn pot is a potentiometer (like your guitar's volume control) that has a lot of turns, so there is a very fine level of accuracy. Taking your amp to a tech is probably a good idea, and have them bias it properly.
Robert S.
Super Moderator
Re: What is tube biasing?
I am pretty sure that the only difference between the 12at7 and the 12 ax7 is the amount of gain. If the noise level doesn't change as you turn the reverb knob from zero to ten then the reverb tube isn't your issue.
Read a few reviews on the Galaxie 25 and all commented on the tube noise so some of that is common for that amp. Different tubes may help reduce that some but a certain amount of hiss is common in all tube amps when they are cranked up. If you cant hear the noise over your playing then you are probably good to go.
If you put a noise gate or volume pedal at the end of your signal chain you can get often get rid of the hiss at idle, turning the guitars volume to zero when you are not playing also usually works.
Couldn't find the operation specs for that amp and I am not great with amp schematics but 25 watts out of 2 el84s is most likely class a/b and the power tubes will need to be biased when you change them. Some music stores still employ part time amp techs and others will refer you to a tech. Having a local amp tech that you trust and that is reasonable is a must have once you get into tube amps. You may only need a tech every year or two+ when it's time to change out your power tubes but if your amp goes down and you need it back quick it's nice to have someone to call.
I am pretty sure that the only difference between the 12at7 and the 12 ax7 is the amount of gain. If the noise level doesn't change as you turn the reverb knob from zero to ten then the reverb tube isn't your issue.
Read a few reviews on the Galaxie 25 and all commented on the tube noise so some of that is common for that amp. Different tubes may help reduce that some but a certain amount of hiss is common in all tube amps when they are cranked up. If you cant hear the noise over your playing then you are probably good to go.
If you put a noise gate or volume pedal at the end of your signal chain you can get often get rid of the hiss at idle, turning the guitars volume to zero when you are not playing also usually works.
Couldn't find the operation specs for that amp and I am not great with amp schematics but 25 watts out of 2 el84s is most likely class a/b and the power tubes will need to be biased when you change them. Some music stores still employ part time amp techs and others will refer you to a tech. Having a local amp tech that you trust and that is reasonable is a must have once you get into tube amps. You may only need a tech every year or two+ when it's time to change out your power tubes but if your amp goes down and you need it back quick it's nice to have someone to call.
misterwhizzy
Well-known member
Re: What is tube biasing?
The schematic has a bias adjustment pot, and it looks like a fairly typical EL84 power section, so I would put good money on it needing to be biased when the power tubes are replaced. For someone with experience, it's no big deal. Even for me, without much experience, it's not that big a deal. But if you're asking what it means, take it in to a tech when you change the tubes. Don't be messing around in there, because there is very high voltage.
The schematic has a bias adjustment pot, and it looks like a fairly typical EL84 power section, so I would put good money on it needing to be biased when the power tubes are replaced. For someone with experience, it's no big deal. Even for me, without much experience, it's not that big a deal. But if you're asking what it means, take it in to a tech when you change the tubes. Don't be messing around in there, because there is very high voltage.
bigmack209
New member
Re: What is tube biasing?
can i get an estimate or some sort of average price for a tube biasing job? just so i know i'm not getting ripped
can i get an estimate or some sort of average price for a tube biasing job? just so i know i'm not getting ripped
misterwhizzy
Well-known member
Re: What is tube biasing?
First of all, how old are your power tubes? Do you know? Does anything sound bad with the amp?
First of all, how old are your power tubes? Do you know? Does anything sound bad with the amp?
bigmack209
New member
Re: What is tube biasing?
central valley, california. near stockton
don't know how old the tubes are but they're sovtek crap and i'm replacing them with JJ's
central valley, california. near stockton
don't know how old the tubes are but they're sovtek crap and i'm replacing them with JJ's
Re: What is tube biasing?
From the Schem posted it looks like you have dual bias isjust....one for each tube that is.
And, as a member already mentioned, they are 10 turn pots. Not sure why, guess it will be apparent when you set the bias.
Speaking of bias, this is not something you are going to be able to do, by yourself, on the first try. You need a decent meter, and know how to split the OT and measure the plate voltage and resistance. I=E/R.
Either that or you need to install some 1 Ohm cat resistors. But them you still need a meter, take some measurements, do the math, and turn the pots.
If you do not have some mechanical aptitude and desire, you will need a tech.
Best
From the Schem posted it looks like you have dual bias isjust....one for each tube that is.
And, as a member already mentioned, they are 10 turn pots. Not sure why, guess it will be apparent when you set the bias.
Speaking of bias, this is not something you are going to be able to do, by yourself, on the first try. You need a decent meter, and know how to split the OT and measure the plate voltage and resistance. I=E/R.
Either that or you need to install some 1 Ohm cat resistors. But them you still need a meter, take some measurements, do the math, and turn the pots.
If you do not have some mechanical aptitude and desire, you will need a tech.
Best
