6L6 AB PPP stage; does it make sense?

[audio_moksha]

Hello folks,

I decided to build a tube amp head running with 2 (or 4) 6L6's PPP Class AB in the power stage to put out 15W (or 30W). I adapted the power amp circuit from the Mesa Boogie Lonestar design. However before I start building it, I wanted to ask the more experienced folks out here if the circuit makes sense. The two things that I'm unsure about is

1. The switch between tubes 6L6(1) and 6L6(2) is what controls the power output. When on, the connection to ground is made and the circuit is now working in parallel push pull to supply 30W output. When the switch is off the ground connection is broken and tubes 6L6(1) and 6L6(2) now work as a buffer stage. Once again, this is how I think this circuit works but am I wrong?

2. I'm still unsure about how to calculate the power output for a class AB PP amplifier. My OPT is a 4000:16/8/4 and so my loadline for 2 tubes (ie with the power switch off) is 1000R. My operating point lies at -22Vgk, Ia quiescent=40mA, B+=360V Iamax=180mA and therefore my maximum rms power is (180mA/sqrt2)^2*1000R (P=I^2*R) giving me 16.2W.

For all four tubes, my loadline is 500R, my Imax doubles to 360mA giving me Po=(360mA/sqrt2)^2*500R = 32.4W.

My maximum plate dissipation is about 15W so the tube should run well. Now is my reasoning sound? The thing thats bothering me is that I don't know how the screen voltage Vg2 comes into the picture. For now I have it running at about 355V. Secondly, does my power estimate take into account the effeciency of the PP topology or do I need to factor in 60% of 16.2W and 32.4W?

Please let me know what you think.

[audio_moksha]

The preamp circuit

[audio_moksha]

ps: You will need a compressing/extracting software to view these attachements eg.WinRar or WinZip. Sorry but I could not find another way to compress these schematic images.