That depends on which S.E.X. amp version you have. Here are the versions:
Original SEX monoblocs (Magnequest upgrade TFA-204)
Revision 1.0 (1996) (Magnequest upgrade TFA-204)
Revision 1.1 (1996) (Magnequest upgrade TFA-204)
Revision 2.0 (1997) (Magnequest upgrade TFA-204)
ParaSEX (1999) (no upgrade)
Stereo SEX
Version 2.0 (2004) (Magnequest upgrade BH-2 choke, BH-1 transfprmer 8 ohms only)
(Bottlehead upgrade PC-3 choke, OT-2 transformer)
Revision 2.1 (2011) (stock Bottlehead PC-3 choke, OT-2 transformer - no upgrades)
Revision 3 (2017) (stock Bottlehead PC-3 choke, OT-2 transformer - no upgrades)