Marshall plexi Preamp question

[jimmy]

The Marshall Plexi comes with three tubes (12AX7s) in the preamp. I would like to know which tubes are being used if I plug into the Top right (II or second) input.

I know this amp has two seperate preamps, but why are there three tubes?

Any help would be great. Thanks

 

[mrid]

Re: Marshall plexi Preamp question

I'm pretty sure that you're using all the preamp tubes regardless of where you plug in. The bottom inputs are probably just attenuated.

 

[jimmy]

Re: Marshall plexi Preamp question

Alright, thanks.

 

[MrHeavyMetal]

Re: Marshall plexi Preamp question

The Marshall Plexi comes with three tubes (12AX7s) in the preamp. I would like to know which tubes are being used if I plug into the Top right (II or second) input.

I know this amp has two seperate preamps, but why are there three tubes?

Any help would be great. Thanks

]

V1= preamp tube 1
V2= preamp tube 2
V3= preamp tube 3

and each 12AX7 preamp tube has two seperate circuits, i.e. V1 and V2 due to their construction.

V1A: 1st Gain Stage
V1B: 2nd Gain Stage
V2A: 3rd Gain Stage
V2B: Cathode Follower
V3A/B: Phase Inverter

Using the low input bypasses V1A to V1B gain stage. Most plexi users however jump both channels so you'll have a full 3 gain stages.

 

[jimmy]

Re: Marshall plexi Preamp question

Thanks for the detailed info, bro.

 

[Jeff_H]

Re: Marshall plexi Preamp question

]

V1= preamp tube 1
V2= preamp tube 2
V3= preamp tube 3

and each 12AX7 preamp tube has two seperate circuits, i.e. V1 and V2 due to their construction.

V1A: 1st Gain Stage
V1B: 2nd Gain Stage
V2A: 3rd Gain Stage
V2B: Cathode Follower
V3A/B: Phase Inverter

Using the low input bypasses V1A to V1B gain stage. Most plexi users however jump both channels so you'll have a full 3 gain stages.

Nailed by the man from middle Tenessee! :smoker: