last year i did a repair to a fender super sonic amp , required an extensive general fix with a few mods i did for improvement , like the ribbon cable that goes from the front controls panel carries audio and is not shielded so i covered it with copper tape and grounded it to the chassis this quieted down a lot of the internal hum. after the repair and all was working I discovered the reverb circuit was not happening at all , so I replaced the reverb transformer, and the transistors in the circuit ,( I ordered the transformer in september 2020 it showed as instock with fender , it finally arrived the end of April 2021 ) after the new parts were in place , no joy , it did not work still , so i tested the return from the reverb tank it was quite alive, so i reversed the reverb cable at the amp and the tank , this tested the cable and it responded just fine , indicating the cable was OK , I measured the tank reisitence the out put was good but the input has 1.7 ohms , so I replaced the tank and it now comes alive , this is all well and great. but during the testing the tank starts to howl at about 6 on the dial I check the cable from the amp to tank and replace it just incase of bad continuity , pack it up and give it back to the very patient customer . last friday i get a call from L&M the customer brought back the amp in it is stil howling at 6 on the dial intermittently so today up on the bench it goes I look very closely at the reverb jacks on the amp and notice the Nylon plate that holds the RCA jacks is held in place with one screw so if by chance the screw works its way out the ground of the tank return shorts to chassis ground creating this howl, ( what a crap piece of engeneering in the design). My fix for this was to cut a piece of sticky 2 sided tape cut 2 holes just big enough for the RCA jacks to poke through covering the out side chassis around the jacks ensuring a zero chance of chassis contact with the jack , and every thing worked perfectly. The poor customer was at the whim of Fender and their bad engineering , after the repair this amp sounded outstanding and really kicked A$$ a nice sounding amp for sure.