Mark IIB Treble Shift Question

[BPski]

Can anyone tell me on the Mk IIB what year the Treble Shift function was latched to the Channel switching? I have an earlier 60w Mk IIB where the Treble Shift function does not switch with the footswitch, just with the Pull-pot. Or was this feature not on the Mk IIB and came later on the IIC and C+?

Thanks for all the help!!

 

[Tuna141]

Unless I misunderstood your question...

I'm unaware of any Mark II models having the capability of footswitching the Treble Shift. I know my Mark IIC does not have this feature.

 

[BPski]

Let me try to clarify. On my Mark IIC+ if you pull the Treble pot it shifts the treble respose. While it is pulled out it only affects the Drive channel and is engaged with the footswitch. I was wondering if this was a feature on the later Mark IIB's.

I hope this clarifies things.

any info is appreciated.

Thank you!!

 

[Boogiebabies]

This feature requires an LDR and only shows up as being automated in the IIC and IIC+ literature.

 

[BPski]

That's what I thought. Has anyone ever had their IIB modified to perform like a IIC or C+?

Thank you.

 

[Boogiebabies]

I do not know, but anything is possible. It really would only require an LDR and a 12V power supply and the switch of course. You may have room on the PCB, but all you are really doing is putting the 750pf and the 250pf in paralell to make it 500pf.

I would give it a shot.

 

[BPski]

Maybe I could use another relay to open and close the switch along with the opening and closing for the channel switching. The suppply is already there. I am going to consult Mike Bendinelli next week. That would be a cool function in this amp.

By the way I thought that capacitors in parallel were additive, the opposite of resistors. So a 250p and 750p in parallel would be 1000p. Thoughts?

Thanks again!!

 

[Boogiebabies]

No, They are not in series. Look at all the modern high gain amps. They use a 500pf for the treble. The Mesa has the standard 250pf like a common Fender tonestack. The 750pf in parallel with the 250pf makes it a modern style tonestack. At 500pf it shifts the treble frequency downward and boosts the midrange. As Mesa calls it in the IIC manual a more "Robust" midrange.

If they were both in series, they would be 1000pf or .001uf. Series adds and parallel subtracts.



Vote for Pedro.

 

[BPski]

Capacitors of equal value in parallel are additive in value with their voltage rating staying the same. Caps of equal value in series are divisible in value by the number of capacitors with their voltage rating increasing by the voltage of each cap in series. Capacitiors behave exactly the opposite of resistors. Example: 2 - 20uF/500V caps in parallel gives you a total of 40uF/500V. 2 - 220uF/350 caps in series gives you 110uF/700V.

Thank you.

 

[Boogiebabies]

It is not a matter of voltage and these are not of equal capacitance, nor are they power supply filter caps. When you put a capacitance meter on a 750pf and 250pf in paralell it shows 500pf. If you want them in series and 1000pf in your tone stack, more power to you. Remember, these are 1000V ceramic disc capacitors.

 

[Boogiebabies]

Say hi to Randall Aiken for me.

 

[BPski]

Capacitors are capacitors. I do not know Randall Aiken

Thank you.

 

[Boogiewan Kenobi]

The IIB had Treble Shift affect both modes, but was more noticable in the lead mode. With the IIC, C+ and III it affected lead mode only. It was never offered as an option to footswitch.

BWK

 

[BPski]

Well I just got another Mark IIB. It is a 1981, Black tolex, 60/100w, Reverb and EV12L. Sounds great. The funny thing is that the Treble Shift only affects the Drive Channel. I looked at the PCB and compared it to my earlier MK IIB and it is different in the Treble cap area. I guess this is stock. Exactly what I wanted. I never use the Treble Shift in the Clean channel. The serial # is in the low 8000's.

Does anyone know when Mesa started making the MK IIB with the Treble Shift affecting only the Drive Channel????

 

[Squigglefunk]

Well I just got another Mark IIB. It is a 1981, Black tolex, 60/100w, Reverb and EV12L. Sounds great. The funny thing is that the Treble Shift only affects the Drive Channel. I looked at the PCB and compared it to my earlier MK IIB and it is different in the Treble cap area. I guess this is stock. Exactly what I wanted. I never use the Treble Shift in the Clean channel. The serial # is in the low 8000's.

Does anyone know when Mesa started making the MK IIB with the Treble Shift affecting only the Drive Channel????

I have a mark IIB and the treble shift only works on the drive channel on mine, 1982, I forget the serial, I think the 9000s.