T
Tonekat
New member
only if you want it to sound good
Since electrical characteristics vary from tube to tube, you need to have the amp biased when replacing the power tubes.
Unless you already own a digital multimeter and are used to fooling around with potentially fatal amounts of current, just take your amp to a qualified amp tech and have it done.
For an informative article on the whys of biasing, check this:
http://www.aikenamps.com/WhatIsBiasing.htm
Since electrical characteristics vary from tube to tube, you need to have the amp biased when replacing the power tubes.
Unless you already own a digital multimeter and are used to fooling around with potentially fatal amounts of current, just take your amp to a qualified amp tech and have it done.
For an informative article on the whys of biasing, check this:
http://www.aikenamps.com/WhatIsBiasing.htm
B
bullyhill
New member
Mesa is pre-biased.
and what he said, nice link.
and what he said, nice link.
Tom Hicks
Well-known member
I've watched my tech do this and...
With a multimeter,he swaps the tubes around and adjusts the little "trim pot" by the tube sockets untill the values are within a volt per pair.The inner two and the outer two are pairs on 4 power-tube designs.If I remember,the nominal voltages are 38-40 volts when these adjustments arre being made.Not a tough job for the qualified.But we are talking about amperages that could kill you,so do find a good tech to rebias your tubes.
With a multimeter,he swaps the tubes around and adjusts the little "trim pot" by the tube sockets untill the values are within a volt per pair.The inner two and the outer two are pairs on 4 power-tube designs.If I remember,the nominal voltages are 38-40 volts when these adjustments arre being made.Not a tough job for the qualified.But we are talking about amperages that could kill you,so do find a good tech to rebias your tubes.
LocusLarsen
New member
c7sus, I like that method, My blues junior hums a bit too much. I don't know if I will just go ahead and start twisting trims and such just yet, but I will look into it. Though it seems like everyone and everywhere is always warning about the serious pinpoint acuracy needed to change tubes rebias that, well, I have to wait on yours for a bit.
dragonworks
Banned
Certain power tubes use different bias votages on the grid. The bias circuit is designed to delliver the proper voltage. The potentiometer in these circuits will only fine tune within the range for the tube designed.
The normal procedure should be to discern the bias required by the present output tubes, and the circuit that delivers that bias voltage to those tubes,
to the bias required by the tube you wish to substitute. If the difference in bias voltage is great enough the bias circuit will have to be modified in order to deliver the necessary bias for the substituted tube.
The normal procedure should be to discern the bias required by the present output tubes, and the circuit that delivers that bias voltage to those tubes,
to the bias required by the tube you wish to substitute. If the difference in bias voltage is great enough the bias circuit will have to be modified in order to deliver the necessary bias for the substituted tube.
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mcmd
New member
.....as far as I know, there is no bias adjustment (trim pot) on the Mesa's....they (Mesa Boogie) pre screen (measure) the tubes characteristics and sell you a tube pair that meets the bias requirements for that amp.....
/Dara
/Dara
LocusLarsen
New member
Well I have a Blues Junior and was thinking about swaping out the power tubes for 6L6, but I don't know exactly how much of a hassle that will be. If even possible. But if I just replace my groove tube EL84 with Mesa brand, that should be fine right. Mesa tubes are probably set to work in their amps without much trouble, but......fuck it.....this is too confusing.....I am selling my damn amp and going back to solid state.
Shit I can't do that.................ahhhhhhhHHHHHHHH!!!!!!!
I still don't even know if I blew my damn tubes.....And I hate going to Guitar Center........
So I read on the internet that swapping tubes with a blown fuse fucks up my NEW tubes if I put them in.....so I have to check my fuse?!?!?!?!.........MY AMPS SOUNDS LIKE A GOD DAMN INFERNO WHEN I TURN IT ON!!!!!!!!!!!!!!!!!!!
?
Hey =) I can rate my own thread.....thats fucking cool..........
Shit I can't do that.................ahhhhhhhHHHHHHHH!!!!!!!
I still don't even know if I blew my damn tubes.....And I hate going to Guitar Center........
So I read on the internet that swapping tubes with a blown fuse fucks up my NEW tubes if I put them in.....so I have to check my fuse?!?!?!?!.........MY AMPS SOUNDS LIKE A GOD DAMN INFERNO WHEN I TURN IT ON!!!!!!!!!!!!!!!!!!!
?
Hey =) I can rate my own thread.....thats fucking cool..........
toyL
Member
The “trim” adjustment on a fender twin will not adjust the bias of the output tubes (unless it has been re-wired to do so). I believe it is designed to be used with a “matched-set” of four tubes—to balance the output of the two “pairs” of output-stage tubes—each pair (in parallel) handles half of the output signal. When you buy new 6L6 tubes you should always order them as a “balanced or matched-set”—which means that the bias voltage and transconductance for each tube are “matched” at the factory. This ensures that the two tubes in each half of the output are conducting the same/equal amount of current. Optimal performance of the amp is not attainable when these currents don't match fairly close.
Check this site out for a more detailed explanation-- http://www.electron-valve.com/
Check this site out for a more detailed explanation-- http://www.electron-valve.com/
toyL
Member
lighten up LocusLarsen...I don't see how you can hurt your new tubes if the fuse is blown...a blown fuse means no current.
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Tonekat
New member
wait a minute!
6L6s in an amp designed for EL-84's? I don't think that's possible, the tube sockets are different.
Also, some of the replies above show that some of those who responded think you have a Mesa amp, which I think is a cathode bias amp that (supposedly) doesn't need biasing (there are those who debate that, but I'm a Fender/Marshall guy).
You have a Fender amp, and were thinking of getting Mesa replacement power tubes only, right?
Just seek out a decent amp tech, and tell him what you want, buy a new matched pair of EL-84s, (if he says you need them) and everything will be groovy. Places like GC usually have some independent guy that comes around and collects what they have waiting for repair, it would be cheaper if you went directly to a tech.
And if you want the 6L6 sound, buy an amp that uses them, like a Vibrolux Reverb.
6L6s in an amp designed for EL-84's? I don't think that's possible, the tube sockets are different.
Also, some of the replies above show that some of those who responded think you have a Mesa amp, which I think is a cathode bias amp that (supposedly) doesn't need biasing (there are those who debate that, but I'm a Fender/Marshall guy).
You have a Fender amp, and were thinking of getting Mesa replacement power tubes only, right?
Just seek out a decent amp tech, and tell him what you want, buy a new matched pair of EL-84s, (if he says you need them) and everything will be groovy. Places like GC usually have some independent guy that comes around and collects what they have waiting for repair, it would be cheaper if you went directly to a tech.
And if you want the 6L6 sound, buy an amp that uses them, like a Vibrolux Reverb.
T
Tonekat
New member
toob talk
With EL-84s, you are pretty much restricted to putting in another pair of those. This is the same tube used in Vox amps, and some of the newer small Ampegs, and a lot of boutique amps like Budda. They have a reputation for a chimey sound (it's a good thing).
As long as nothing else is wrong with your amp, you could probably get away with swapping in another pair, but why settle for that when you can get the best tone out of it by having it biased?
I have found that a little tweaking makes a big difference in the sound. And good preamp tubes will affect your tone too, even if you just get one good 12AX7 in the phase inverter position.
If you really want some help from tech types and experienced amateurs, try the vintage amps bbs at:
http://vintageamps.com/PlexiPalaceUBBcgi/ultimatebb.cgi
They may be able to point you to a good tech in your area.
With EL-84s, you are pretty much restricted to putting in another pair of those. This is the same tube used in Vox amps, and some of the newer small Ampegs, and a lot of boutique amps like Budda. They have a reputation for a chimey sound (it's a good thing).
As long as nothing else is wrong with your amp, you could probably get away with swapping in another pair, but why settle for that when you can get the best tone out of it by having it biased?
I have found that a little tweaking makes a big difference in the sound. And good preamp tubes will affect your tone too, even if you just get one good 12AX7 in the phase inverter position.
If you really want some help from tech types and experienced amateurs, try the vintage amps bbs at:
http://vintageamps.com/PlexiPalaceUBBcgi/ultimatebb.cgi
They may be able to point you to a good tech in your area.