The last, "vintage" amp that I modded, was an ST-70. I found that the PC could be upgraded, without having to butcher the chassis. At that time, Zu’s Birth was an inexpensive and small(3/8" - 9.5mm) power cable, that easily fit through the original chassis access, protected from abrasion by a new rubber grommet, after removing the stock cord and strain relief. A couple Nylon cable/zip-ties, inside the chassis, on the cable(not so tight as to crush anything), to prevent extraction. Not certain whether they still offer the Birth, but- their Mission PC has almost the same diameter(less than 1 mm larger) and basic construction. The swap provided an obvious/audible improvement, in the ST-70’s presentation(done more than once, actually). Just save the stock cord and strain relief, which can easily be replaced, if desired. https://www.ebay.com/sch/i.html?_from=R40&_trksid=m570.l1313&_nkw=Zu+Audio+MISSION+Power+Cabl&_sacat=0 There’s also a Mk II: https://www.zuaudio.com/cable/mission-power-ii
