Hello Bifwynne , yes it is a DIY upgrade ,I have the schematics of my REF3 and with the help of an REF5se owner
it was easy for me to see where to connect the wires and which components were used ( all components like the ARC originals easy to order at the WEB )Two years ago the coupling caps and the two output tubes were replaced by a high quality output transformer.The cheap and lowclass rectifiers in the highpowerunit were replaced by highclass ones and an extra capacitor added at the end of the 6550 output line to the two output tubes .Up until now I have not been able to compare my REF3SE with the REF5SE , but I think , and what I noticed with other audiofriends , this is a REF5SE and 6SE and 7 SE killer.
it was easy for me to see where to connect the wires and which components were used ( all components like the ARC originals easy to order at the WEB )Two years ago the coupling caps and the two output tubes were replaced by a high quality output transformer.The cheap and lowclass rectifiers in the highpowerunit were replaced by highclass ones and an extra capacitor added at the end of the 6550 output line to the two output tubes .Up until now I have not been able to compare my REF3SE with the REF5SE , but I think , and what I noticed with other audiofriends , this is a REF5SE and 6SE and 7 SE killer.