Biasing equipment

[konstantine RK]

I was watching YouTube and saw this multimeter looking thing with wires that piggybacked power tubes into the amp like an extenstion for vacuum tubes.

I believe the man on the video said it was called a " TAD bias master"?

Anyone know what this thing actually is called and is it set to just bias tubes?

 

[94Tremoverb]

There are various versions with different names like 'Bias King', 'Bias Rite' etc - they're all essentially the same thing, which is a plug adapter that goes between the amp and the tube and lets you monitor the tube current, either with a supplied meter or any standard multimeter. Basically they are no more than a plug and a socket with a 1-ohm resistor in the cathode path to the tube, which is the simplest and safest (though not quite most accurate) method of checking the bias.

They aren't much use for a standard Mesa amp, other than to just check that the tubes are in the right range for the amp, since Mesa amps do not have adjustable bias. In fact, if you use one with a Mesa you will be shocked at how 'cold' (given current fashion and supposed wisdom for running tubes as hot as possible without actually melting them) the tubes are running. Though this does not seem to make them sound bad...

For what it's worth, I fitted a variable bias control to my Tremoverb - just because I can, and I was interested in being able to tweak it, and run other than the recommended tubes - and was surprised how *little* difference it made to the tone. Not none, but certainly not the night-and-day difference that people who insist on variable/hot bias will tell you.

 

[konstantine RK]

thanks for the info 94tremoverb! What about matching your tubes though? Is that a concern with Mesa amps like the Roadking?

Or can you literally just plug your tubes in and go?

 

[94Tremoverb]

As long as all the tubes are Mesa tubes (or rated by other vendors for Mesa amps), just plug and play. You can mix 'color' types if you want - in the 4-tube section it's best to balance it with one pair in the inner sockets and the other in the outer, but apart from that it doesn't matter. The worst that will happen is a small amount more hum, if the tubes aren't all perfectly matched.

 

[Old BF Shred]

There are various versions with different names like 'Bias King', 'Bias Rite' etc - they're all essentially the same thing, which is a plug adapter that goes between the amp and the tube and lets you monitor the tube current, either with a supplied meter or any standard multimeter. Basically they are no more than a plug and a socket with a 1-ohm resistor in the cathode path to the tube, which is the simplest and safest (though not quite most accurate) method of checking the bias.

They aren't much use for a standard Mesa amp, other than to just check that the tubes are in the right range for the amp, since Mesa amps do not have adjustable bias. In fact, if you use one with a Mesa you will be shocked at how 'cold' (given current fashion and supposed wisdom for running tubes as hot as possible without actually melting them) the tubes are running. Though this does not seem to make them sound bad...

For what it's worth, I fitted a variable bias control to my Tremoverb - just because I can, and I was interested in being able to tweak it, and run other than the recommended tubes - and was surprised how *little* difference it made to the tone. Not none, but certainly not the night-and-day difference that people who insist on variable/hot bias will tell you.

So its not just me! :mrgreen:
This is what I found and I have been "smeared" (I mean that in jest, btw) by others on this board for reporting it. I put a trim pot in my 50/50 and am surprised by only a slight change in tone. This perhaps is due to the Mesa design compared to other amps (at least I have been told this by 2 Mesa repair techs in my area, though the transformer would likely be the root of this....).

I think the big advantage of adjustable bias in a Mesa is the ability to use a wider variety of available tubes.
I will say that I do hear a difference as the tubes get hotter with use. And if you think about it, the higher idle current will certainly warm up a tube faster so that makes sense. But when playing a gig from say 9pm to 1am(ish), they definitely get hot enough and quickly enough!

As far as a tool, I made my own adapter with male & female octal sockets and a 1 ohm resistor. Then I just use a standard meter to measure the voltage drop across the resistor. I won't say it is super accurate, but seems to be within 10% or so which is fine for me.
Commercial or home brew, I think they are worth having....
Good luck!
C ya!

 

[dodger916]

I think the big advantage of adjustable bias in a Mesa is the ability to use a wider variety of available tubes.

Yup.

I will say that I do hear a difference as the tubes get hotter with use. And if you think about it, the higher idle current will certainly warm up a tube faster so that makes sense. But when playing a gig from say 9pm to 1am(ish), they definitely get hot enough and quickly enough!

Yup again.