software

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

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.

Alright, thanks.


Originally Posted by jimmyThe 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.

Thanks for the detailed info, bro.


Originally Posted by MrHeavyMetal]

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!