Re: .68uf cap on presence pot? 
 

I'm not Speed or Trace, but 0.68uF on the presence pot beefs things up a bit. I actually prefer 0.47uF, but it's a subtle difference.
 
If you want a lot of gain, try bypassing V2A cathode resistor with 0.68uF, or even bigger if you want a lot of mid. It can make things a little fizzy, but it's worth a try.
 
Liam

replace the first resistor (10k) with a 4.7k my 79 50 watt is so addictive now I never want to turn it off..

I'm not Jerry, but think he means the 10k cathode resister on the 2nd stage of the master volume preamp