Mark IV with IC chips....used for what?

[dodger916]

This Mark IV auction http://cgi.ebay.com/Mesa-Boogie-Mar...39:1|66:2|65:10|240:1318&_trksid=p3286.c0.m14

includes three IC chips. What are these used for?

Thanks.

 

[Boogiebabies]

Channel switching circuits.

 

[mr_fender]

I thought I remember reading somewhere that the Graphic EQ is FET driven too. I might be wrong on that though. There's quite a bit of silicon on the board of a mark IV, though I believe the signal path is nearly all tube.

 

[Boogiebabies]

The GEQ is amplified with NPN and PNP transistors. Other than that it's all tube.