I just upgraded an old stand-a-lone Fender reverb unit. Installed a newer three spring tank, new control knobs, and RCA cables. The cables that came with the unit were black plastic covered (not original vintage). I purchased new vintage style cables but had to cut to proper length and resolder the connects. After checking for proper continuity I plugged in these new cables and got little to no reverb. I tapped on the tank and got some reverb through the amp speaker, so I know the cables had to be working. So I plugged in the old plastic cables, and It sounds great. Why would I not get reverb from these new vintage style cables?