The value is 3.15AL for 117 volts and 1.6AL for 230volts. The schematic is available here:http://www.ampix.org/albums/userpics/10003/MArshall_MG100DFX.pdf I know it's not exactly the same model but I'm pretty sure that it's going to work in your case.Here is the support site if you want to ask them:http://www.marshallamps.com/support/support_contact_us.asp Please let me know if this helps.
Answers & Comments
The value is 3.15AL for 117 volts and 1.6AL for 230volts. The schematic is available here:http://www.ampix.org/albums/userpics/10003/MArshall_MG100DFX.pdf I know it's not exactly the same model but I'm pretty sure that it's going to work in your case.Here is the support site if you want to ask them:http://www.marshallamps.com/support/support_contact_us.asp Please let me know if this helps.