subway blues amp

[jmichaelbohn]

I have a Mesa amp...4 12x7...2 EL84s......
I need to know which posiyion is V-1 and what EACH pre-amp tube does.....
Mesa doesn't want to tell me....( I promise I won't blow it up.....right away..)
I just want to substute lower gain tubes in the right places......thanks in advance...jmb

[Enzo]

The people at Mesa don't have enough time in the day to have extended conversations explaining the engineering behind their products. It ain;t personal. Their amps are very much like any other company's amps - they all have an input stage, they have EQs, they have gain stages, they have phase inverter stages and they have power tube stages. These progress along through the circuit. One of your tubes drives the reverb and handles the return.

If you already have some lower gain tubes - either 5751 or 12AY7 or whatever lower gain types, or simply 12AX7s selected for lower than average gain - the simple solution is to start with the first socket on the end and try the various tubes there. See which ones sound better to you. Take notes. Now put the original tube back and move to the second socket, try the selections there. Take notes. Restore the original tube each time. Why? Because we want to get to know how each socket affects the sound you already know. Once you know what tubes sound best in each place, try making all the changes you seem to like. You might find that individually you like certain tubes, but when combined, maybe not so much. And at that point you experiment some more.

[jmichaelbohn]

which one is the PI??????

[Enzo]

Usually the one closest to the power tubes.