I've been looking over the layout several times now, so I believe it should be safe to build.
Recommended mods/stuff to try out:
- Put the 4.7nf input cap on a switch with a 47nf in the other position for more dirt and bottom end.
- Flip the transistors 180, you will get more grit and gain out of it. IOW: they work both ways (probably due to leakage), so socket the transistors and try it out!
I have not tried Silicon transistors.
I kinda got a fetish for Germaniums because of the great picking dynamics and guitar-volume cleanup I get from them compared to Silicon, so the idea never struck me...
But try it!
The design is pretty much a standard amp sim circuit in the style of the Superbolt, so it should work.
But I suspect you will have better luck with JFet transistors, as that is what normally is used in amp sim circuits, because of the similarity they have in character to tubes.
You probably need to socket the 33k resistors though, to get the bias correct if not using the 103NU71's.