12AX7 in starving mode Dynaco PAS3X

[Kmet]

Hi there..

I make Dynaco clone of the famous PAS3X preamp (only the line stage) and I am very pleased with sound of this preamp. Some recordings are truly natural and fine to listen. Now I want to make analysis of the circuit and to solve puzzle of this sweet preamp.

My mindcrunching question is: whay did designer of this preamp make heather of the 12AX7 tubes on smaller voltage, 12xx tubes are
12,6Vdc but in preamp it is 11Vdc on heather. One reason will be longest lifespan of tubes but it is unlikely..
How this particular tubes works in heather starved mode?

I found some schematics of the HP tube voltmeters with input tubes in starved mode. Please give me some hints..thanx

Solder smoke lover from Croatia

 

[DF96]

Slightly lower noise and smaller grid current?

 

[Kmet]

How aplification factor and internal resistance corespodent with lowering heather activity?

 

[DF96]

A cooler heater would mean reduced transconductance g_m, higher anode resistance R_aand probably virtually unchanged amplification factor mu.