Mark IIC+ Bias

[BPski]

Does anyone know the factory value of the bias resistor in the bias supply of a Mk IIC+ Simul? Also the factory setting of the negative voltage and plate current? I believe the voltage is -61 volts.

Thanks!

 

[Boogiebabies]

They are all different depending on the power section. Is it a super 60, 60/100 or a simul?

 

[Mrmot]

sorry for jumping in, you're talking on biasing?
but don't all mesa amps have fixed bias, meaning, it doesn't have to be regulated whenever you install new tubes? i remember reading in the dc-3 manual randall smith saying that he's been making fixed bias amps for the last 25 years because he wanted to evade all the hassle about biasing an amp/taking it to a technician for a bias?

 

[BPski]

It is a Simul Class Mk IIC+. I'd like to know the fatory specs of the bias resistor value, the negative voltage and plate current. Thank you.

 

[RussB]

Fixed bias means only one thing, that the control grid receives a set voltage from a bias supply.

All fixed bias amps CAN be adjusted, either by a potentiometer (which is an adjustable resistor) or swapping resistor values.

 

[Mrmot]

Fixed bias means only one thing, that the control grid receives a set voltage from a bias supply.

All fixed bias amps CAN be adjusted, either by a potentiometer (which is an adjustable resistor) or swapping resistor values.

they can be adjusted, but isn't neccessary like on most other amps, right? I have a studio 22+

 

[Boogiebabies]

It is a Simul Class Mk IIC+. I'd like to know the fatory specs of the bias resistor value, the negative voltage and plate current. Thank you.

PV at pin 3 - 478 Volts ( Dependent on tube draw, mine read 473)

Bias - Red/Blue - LV tap- 470ohm-33K-10K tied to two 50uf 75V caps.

Remember that to get to pin 5, the 6L6's pass through a 2.2K and the EL34's through a 220K.

Bias at tube pin 5 - 6L6's -56V and EL34's - 45V.

All three of mine have these values and are within -1 of each other.

 

[BPski]

It is a Simul Class Mk IIC+. I'd like to know the fatory specs of the bias resistor value, the negative voltage and plate current. Thank you.

PV at pin 3 - 478 Volts ( Dependent on tube draw, mine read 473)

Bias - Red/Blue - LV tap- 470ohm-33K-10K tied to two 50uf 75V caps.

Remember that to get to pin 5, the 6L6's pass through a 2.2K and the EL34's through a 220K.

Bias at tube pin 5 - 6L6's -56V and EL34's - 45V.

All three of mine have these values and are within -1 of each other.

Thanks for the info. I will have to check this all out. Didn't the Simul C+'s come with all 6L6's?

 

[Boogiebabies]

Not all of them did. They came with STR 415's and STR 416's or all 4 STR 415's. The outer sockets, regardless of tube type is -45.

 

[snowman3000]

It is a Simul Class Mk IIC+. I'd like to know the fatory specs of the bias resistor value, the negative voltage and plate current. Thank you.

PV at pin 3 - 478 Volts ( Dependent on tube draw, mine read 473)

Bias - Red/Blue - LV tap- 470ohm-33K-10K tied to two 50uf 75V caps.

Remember that to get to pin 5, the 6L6's pass through a 2.2K and the EL34's through a 220K.

Bias at tube pin 5 - 6L6's -56V and EL34's - 45V.

All three of mine have these values and are within -1 of each other.

Great! And what about the bias on the 60/100 version?

 

[BPski]

My C+ had a 10K instead of the 33K bias resistor. I changed the 10K to the stock 33K. I have -58 volts on the 6L6's and -48 volts on the EL34's. The amp sounded better with the 10K resistor. Current draw was higher I guess. I may change it back. I will post if I do.

Thanks again for the info!!

 

[Boogiebabies]

It is a Simul Class Mk IIC+. I'd like to know the fatory specs of the bias resistor value, the negative voltage and plate current. Thank you.

PV at pin 3 - 478 Volts ( Dependent on tube draw, mine read 473)

Bias - Red/Blue - LV tap- 470ohm-33K-10K tied to two 50uf 75V caps.

Remember that to get to pin 5, the 6L6's pass through a 2.2K and the EL34's through a 220K.

Bias at tube pin 5 - 6L6's -56V and EL34's - 45V.

All three of mine have these values and are within -1 of each other.

Great! And what about the bias on the 60/100 version?

Your kidding, right?

Well, using your amp photo's from 5/27/04 before the Simul upgrade it shows:


LV tap - Red/Blue - 470ohm-4.7K-10K and another 10K tied to the 50uf 75V bias supply caps. The negative voltage at pin 5 should be -52 volts.

 

[Boogiebabies]

My C+ had a 10K instead of the 33K bias resistor. I changed the 10K to the stock 33K. I have -58 volts on the 6L6's and -48 volts on the EL34's. The amp sounded better with the 10K resistor. Current draw was higher I guess. I may change it back. I will post if I do.

Thanks again for the info!!

That is very close to the factory values. Now it really depends on the natural current draw of the tubes in use and how they read in relation to their max plate dissipation. the bad side for some people of Boogie's set bias. You are forced to play the tube draw game. A bias meter will be the only way to find out what the difference would be. To my ear, Boogie's are just not designed around 75% MPD. They are generally colder but offer massive headroom and long tube life on a tube that draws just enough to get out of it's own way. A -30 or -35 on the tube is as high as I go or it seems too muddy for me.

 

[BPski]

You may have my amp confused with another one. I have never posted photos and it was not a Simul conversion. It is original. I still say the 10k resistor sounded better than the 33k. Strange.

 

[Boogiebabies]

The answer is for Snowman3000/Nicko. Notice the 60/100 version at the bottom. You were answered as a Simul.

 

[BPski]

Yep, my bad. Thanks again!!!

 

[Boogiebabies]

No problemo.

 

[snowman3000]

Your kidding, right?

Well, using your amp photo's from 5/27/04 before the Simul upgrade it shows:


LV tap - Red/Blue - 470ohm-4.7K-10K and another 10K tied to the 50uf 75V bias supply caps. The negative voltage at pin 5 should be -52 volts.

BAH! I'm not kiddin' dude! I have those ol' pics in Italy :roll:

 

[snowman3000]

BTW What kind of BIAS setting do i have?!

http://img.photobucket.com/albums/v210/bionuker/2Cplus/1.jpg

I see: 470ohm - 10K - 10K and then 33K wired on one of those little cap!?

 

[Boogiebabies]

The problem with that one is it was not only a + upgrade, but a simul upgrade. The bias resistors are different, but that really says nothing. It is totally dependent on the power transformers low voltage tap and how much resistance is needed to get it to Mesa specs. The bias could be simply modified as well to suit the owner or an under performing/ Over performing LV tap. Also, it is a 100 PT not a 105. That may be the difference alone. Schematic wise, it looks correct for a IIB and IIC with the 100 and the exeption of the added resistor across the top cap.