The trace over at the FSB forum was made be me. I found that there are different versions of the Erupter. Some have an additional Volume-Trimmer to set the output volume and also some seem to have 2 bias trimmers additional to the Bias pot. So you can include an additional volume control if you like. It should be a 100k.
Edit: I'm not sure what the notes about the transistor hfe really means. Does it mean, they should both have about the same hfe in the range of 60-120 with Q3 being the higher? Or does it mean Q2 should have around 60 and Q3 should have around 160 hfe?