Purpose of C12 and C13?

[MagnusBack]

Wondering what the purpose/function of C12 and C13 is in this schematic?
I'm assuming C13 is added because C12 was less than ideal?
(It's from a Sansui AU-717 driver board).
Anybody who can explain?

 

[daqvin_carter]

Looks like it is an electrolytic bypassed with a film cap. It is part of a bias spreader circuit using TR06 along with vr03 for bias adjust. Might be worth replacing c12 and just testing c13.
The purpose is to not allow a change for ac and allow some dc value to set output bias.

 

[wahab]

C13 improve the AC short at high frequencies of the CE junction, since C12 being an electrolytIc has some serial built in inductance.