What tube does what in a MKIIa

[jdandry]

I know what V1, V4 & V5 does but I'm a little confused about V2 & V3 . So is V2 side a and b, gain stages for the normal channel? Is V3a the Lead channel gain stage and V3b for reverb driver? I'm just trying to pick tubes and wanted some help on the function of each slot. Thanks- John

 

[Boogiebabies]

This may help if it is a IIa with a fetron.


http://www.tubefreak.com/mk2.gif

 

[RussB]

Download the owner's manual from the Mesa website

 

[HawnkyTawnk]

+1 to revive an old thread --

I have a Mark IIA head and I'm no schematic expert. Does someone have a short description for V2 & V3? Is half of V4 for Lead like the Mark IIC?

I've looked at Mesa's site and for some reason, the Mark IIA is not on there. The Mark IIB user manual doesn't mention tube duties.

Thanks ---

 

[kaluablue]

V1 a/b are 1st preamp stage with tone controls in between
V2 a/b is the output driver in front of the master control
V3 a is the lead channel drive stage
V3 b is reverb output driver
V4 a/b are reverb input driver
V5 is phase inverter

 

[carlosasi]

What does the a/b in V1, V2 and V3 a/b relate to? Is this a relay?

 

[Boogiebabies]

What does the a/b in V1, V2 and V3 a/b relate to? Is this a relay?

Each 12AX7 has two tubes, or twin triodes in one bottle. They are then broken down to side A or Side B. For example, pins 1,2 and 3 would be used on A and pins 6,7 and 8 for B. With nine pins total, this leaves pins 4,5 and 9 for the heaters. So when broken broken down for task charts or schematics for a IIA, the V1 A using pins 1,2 and 3 would be the input circuit and V1B using pins 6,7 and 8 for the recovery stage for the tone control circuit. All this wonderful stuff is all in one little 12AX7.

 

[kaluablue]

Nope, they are tubes.
Preamptubes of type 12ax7, 12at7 ... as used in Boogies contain two independent units (triodes) referred to as 'a' and 'b', which can be used for different purposes in the circuit.
One unit in V3 is used for overdrive, the other one for picking up the output signal from the reverb spring.
In V4 and V5 both units are used (almost) identically so a/b is not mentioned.

 

[kaluablue]

BB was faster ;-)

 

[HawnkyTawnk]

Dieter --

Thanks a million for a quick reply and short preamp summary.

 

[carlosasi]

Each 12AX7 has two tubes, or twin triodes in one bottle. They are then broken down to side A or Side B. For example, pins 1,2 and 3 would be used on A and pins 6,7 and 8 for B. With nine pins total, this leaves pins 4,5 and 9 for the heaters. So when broken broken down for task charts or schematics for a IIA, the V1 A using pins 1,2 and 3 would be the input circuit and V1B using pins 6,7 and 8 for the recovery stage for the tone control circuit. All this wonderful stuff is all in one little 12AX7.

NICE! So much in a little bottle. Makes me feel better about buying some JAN Philips 12AX7WA to play around with.