[Amps] complicated Bias circuit

[Paul Decker]

Hi builders.

Hopefully you all can view this schematic.

I'm trying to understand what T2 and associated circuitry do.  D17 and D18 seem like a simple bias circuit as SW3 selects between "class C" and "class AB1"  It seems opening R20 puts tube in standby (RX).

What is the point of having 24VDC from T2?  Is it to have a smaller wattage D17 and D18?


https://scontent-a.xx.fbcdn.net/hphotos-frc1/t1.0-9/10289874_10202768703951918_1823401065078063020_n.jpg


Thanks in advance,
Paul