Ampeg SVT-VR&CL ground loop hum solution

[nevetslab]

Hi,
This is Glen (Mars Amp Repair). Well, I would assume since Nevetslab couldn't get the mounting screw that Ampeg was using to mount the regulator thru the plastic insulator washer, then using the mica insulator would not deal with the screw connecting the metal tab to the heatsink. .
Thanx, glen

YUP, that was the problem regarding mounting the existing metal tab 7812T regulator. I did grease up a mica insulator prior to fiddling with Ampeg's mounting screw, and didn't try modifying the tab of the regulator soldered in place to use a larger insulated washer. That's why I went with the fishpaper insulator to prevent possible connection to chassis by the height of the heat sink. Probably wouldn't have mattered, considering I had to scrape away the power coat paint to get the grounding standoff of the SVT-VR to finally serve as grounding continuity from PCB GND to Chassis GND.

So, at the present, the amp is set aside waiting for the insulated case 7812T parts to arrive. I was hoping the fishpaper insulator would have been the alternate solution to that second hum path. I haven't yet severed the 7812T GND connection to the mounting PCB connection to the heat sink. I'll deal with that when I replace the regulator.

I don't recall when the SVT-CL was created, but gather it was well after the SVT-VR was created from the original SVT amps, as it's much like the original in concept electrically. I service far more SVT-CL's than that of the SVT-VR, and as a bass player, I'm more partial to the SVT-CL for tone, but that's just me. Both amps suffer the same problems of loose hardware out of the box, followed by eventual failure and needing repair to get what Manufacturing failed to get right before shipping them out. Keeping a rental fleet of more than twenty of both varieties over the years has led to simple revisions to minimize tube breakage, or loss of chassis mounting screws, etc. Keeping the S/B switch from generating AC Buzz in the Normal Ch of the SVT-VR is a bit more tedious, having to fold up/solder brass shield to mount onto the S/B switch and shield the input circuit of Normal Ch living right next to that switch, etc.

[Mars Amp Repair]

Yes, I would imagine you'd see all kinds of issues with road worn rentals! I never ran into the STB switch creating buzz in the normal channel, but it has been years since I've even seen one of those. Good luck...glen