Mark IIC+ tube replacement/bias question

[Stratmeister]

As a new MkIIC+ owner, and amateur amp tech/restorer, I have a question or 2 maybe I can get some opinions on from the forum.

Anybody ever use power tubes other than Mesa branded ones? My non-simulclas IIC+ is apparently fixed bias, but that assumes you use Mesa tubes of a certain rating I've heard. Other brands may or may not fall in this same "rating" of current/voltage/saturation whatever the metric is.

I've done a lot of work on old Fenders and use lots of NOS tubes. I have to actually mount and burn them in, measure them to find matched pairs. When I do I always have to bias them either through a pot adjustment or changing a resistor value. I know about the whole safe range/saturation thing, but I also know tubes vary by extreme amounts.

So, if I want to use some of my favorite matched pairs of NOS tubes I doubt the MkIIC+ will be "perfectly" biased as Randall wanted it, -54V I think I read.

Is it common to change power tube brands?
Does anyone ever mod these to have adjustable bias?
Does anyone bias these at all?

Thanks for filling me in on the world of Boogie, and straightening me out on bias requirements for this beast.

 

[JDGuitaristT]

It is normal for people to branch outside of Mesa tubes. Mesa recommends a hardness of 5 for your power tubes. I use SEDs and I think they sound great.

I've never had the desire to have adjustable bias? I just swap um and turn it up!

Enjoy!

 

[Stratmeister]

What is "hardness"? That must be a Mesa term for their tube rating of some sort...

 

[JDGuitaristT]

Yep.

 

[Paul Secondino]

I generally don't like the CHinese tubes and Russian tubes that Mesa relabels and puts in their amps. I much prefer JJ electronics tubes. However, I only use JJ tubes that come thorugh www.eurotubes.com

That being said, Mesa biases many of their amps too cold to sound right. So modding the amp is simply a matter of lifting 1 or 2 resistors from the board and replacing it with a slightly lower or higher resistor. Adding a trim pot (variable resistor) is a little more coplicated because you have to predict the correct values to use.

As far as biasing tubes, there is a basic formula of max dissipation divided by plate voltage. IF you are biasing 6l6 tubes which have a max dissipation of 30 watts, you would divide the number 30 by plate voltage which might be 500 or 550 volts. Take that number and divide it by 75% and that approximates where your bias should be set at.

You should not exceed 75% of the max dissipation of the power tube. I generally don't have to mod any of my amps. I jsut relied on Eurotubes to select the proper ones for me and he always does. Great service.

But if I didn't have eurotubes to rely on, I would mod my Mesa amps to have a trim pot and adjust the bias myself.

 

[Boogiebabies]

JJ's in a IIC+ are dull as far as power tubes and lifeless as far as preamp tubes. I'll take a Mesa label 5881 or STR 440 over Bob Pletka's bravado.
Biasing a Mesa is just finding a rating of tube that draws enough natural plate current to get passed crossover distortion. Most of the time it scares me to think that people who do not know what they are doing are taking plate voltage readings. One slip and your *** will be blown across the room and a big blue flash will follow you. Hopefully you live. Learn how to bias and amp and get good bias meter. A Mesa in Grey should get you going.

 

[Stratmeister]

... One slip and your *** will be blown across the room and a big blue flash will follow you...

LOL! What a great description... I learned this lesson young when I decided to figure out how a reel-to-reel tape recorder worked. Pulled the chassis and figured it had to be plugged in to work, right? That first two hand grab of the frame kept me shakin' until it finally dropped from my poor burnt hands and hit the floor. Learned a great respect for electricity that day. I went on to get an Electrical Engineering degree, never to get stung again. And one hand has been behind my back or in my pocket ever since...

 

[LHanson]

... One slip and your *** will be blown across the room and a big blue flash will follow you...

LOL! What a great description... I learned this lesson young when I decided to figure out how a reel-to-reel tape recorder worked. Pulled the chassis and figured it had to be plugged in to work, right? That first two hand grab of the frame kept me shakin' until it finally dropped from my poor burnt hands and hit the floor. Learned a great respect for electricity that day. I went on to get an Electrical Engineering degree, never to get stung again. And one hand has been behind my back or in my pocket ever since...

OWWW! Had a similar experience replacing a start cap in an air conditioner once. Only once. Won't EVEN tell you about the time I shorted a leg of 440 3-phase with a Gerber multi-tool, but thank god I was standing on a milk crate at the time. I don't even remember hitting the floor.....

 

[MesieBooga]

From an earlier Post:
IIC+ Simul tubes
Yes, the inside pair need to be gray. The outside pair should be red.
Mesa scale Groove Tubes scale
Red 4
Yellow 4
Green 5
Gray 5
Blue 6
White 6

The outer sockets, regardless of tube type is -45

 

[Boogiebabies]

... One slip and your *** will be blown across the room and a big blue flash will follow you...

LOL! What a great description... I learned this lesson young when I decided to figure out how a reel-to-reel tape recorder worked. Pulled the chassis and figured it had to be plugged in to work, right? That first two hand grab of the frame kept me shakin' until it finally dropped from my poor burnt hands and hit the floor. Learned a great respect for electricity that day. I went on to get an Electrical Engineering degree, never to get stung again. And one hand has been behind my back or in my pocket ever since...

I had always used the one are style. I was working on a Marshall with a grounding problem and it was a hot day. I leaned over to look into the chassis and I guess a sweaty hair on my left arm hit the chassis. The 480V's went through my left arm through my head and to my left arm. It was a very nice blue though as I dropped to my feet. My teeth were numb for hours.

 

[MesieBooga]

JJ's in a IIC+ are dull as far as power tubes and lifeless as far as preamp tubes. I'll take a Mesa label 5881 or STR 440 over Bob Pletka's bravado.
Biasing a Mesa is just finding a rating of tube that draws enough natural plate current to get passed crossover distortion. Most of the time it scares me to think that people who do not know what they are doing are taking plate voltage readings. One slip and your *** will be blown across the room and a big blue flash will follow you. Hopefully you live. Learn how to bias and amp and get good bias meter. A Mesa in Grey should get you going.

I agree on the JJ's with the IIC+'s/Mesa's. Dull city!