Mystery tube (to me)

[MacGwyn]

Working on a new 18 watt TMB project without the benefit of a schematic, just a layout drawing.  I haven't been able to figure the purpose of preamp tube V3.  Both channels use the two sides of V1 as a preamp and V2 is the phase inverter.  I'm sure someone can take a look at the layout and quickly tell me what function V3 is performing in this amp.  Learning as I go... Thanks!

[sluckey]

V3 is the second voltage amp and cathode follower tone stack driver for the TMB channel.