Runt 50 Boost Function- What Does it ACTUALLY Do?

[M@tt C]

I've been experimenting with my Runt 50 and the boost function, and wondered what engaging the boost actually does in the circuit.

After keeping it on almost from almost Day 1 I've found I actually like it better off and the gain up to almost max- it's clearer, more dynamic, and a little more raw.

To my ears the boost bumps up the low mids, (or cuts the high mids?) and adds more gain and compression. But how? Clipping diodes? EQ shift?

Anyone know? Mr. Friedman??

 

[ZEN Amps]

I had one open a while back but don't recall exactly - I think it was a simple RC value change on a cathode, not an extra tube or diode stage. I may have some pictures somewhere...