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Our Ampeg SVT Classic Vintage (1987 Limited Edition, #178 of 500) came back from a rental with the Volume knob broken and the Bass control's knob & shaft broken off. 1/4" dia Single-D Nylon shafts on all of the pots. I hadn't removed the rest of the knobs before ordering seven new Ampeg replacement knobs, though the set that was installed, all but the Volume knob from Ch 1 had their faces sanded smooth and new indicator lines cut into the surface. I vaguely remember having to do that though didn't remember why. After ordering the knobs, grumbling a bit about paying $4 per knob, I had removed the knob next to the Ch 1 Volume pot, then saw why. All but Ch 1 Volume pots had their Flat 180 deg rotated from that Ch 1 Volume pot. The indicator lines would be reversed. I hadn't spent time to search for an alternative knob type that had dual set screws. And, with another standard SVT-CL that had come in, I looked at it, whose single-D shaft all matched the one control that didn't require a non-standard knob.
So, I tried a different approach this time. Using some 3M Mylar tape, I masked off the surface using the stock indicator line as a guide, leaving an exposed knob surface where I was going to apply some white enamel paint for a new line, then scrape off the old line, and use some very fine sandpaper (2000 grit) to remove the tool marks from scraping off the old line. As careful as I was, I still was greeted with seepage underneath the mylar tape. I did at least escape having it seep down onto the short radial surface above the fluted surface. Took a while to get thru the six knobs, and looking close, I wasn't all that happy with the results, but, after I had sanded the surface around the new line, and used a bit of nose oil with my thumb to rub into the sanded surface, it came out ok. At a glance, who's gonna know?
Still more work than I had intended to do. Getting that preamp out of the cabinet was a PITA, since the bulk of the mounting screws are along the back flange on the roof of the cabinet, so either remove the power amp chassis, or remove the power tubes, and curse when you can't get anything but a right-angle ratcheting Philips screwdriver in where the two xfmrs disallow any size of normal scrrewdriver to remove those two. The front screws are right above the front side-wall cleats. No service loop on the bass control, which was the pot whose shaft broke. All in a days work.
So, I tried a different approach this time. Using some 3M Mylar tape, I masked off the surface using the stock indicator line as a guide, leaving an exposed knob surface where I was going to apply some white enamel paint for a new line, then scrape off the old line, and use some very fine sandpaper (2000 grit) to remove the tool marks from scraping off the old line. As careful as I was, I still was greeted with seepage underneath the mylar tape. I did at least escape having it seep down onto the short radial surface above the fluted surface. Took a while to get thru the six knobs, and looking close, I wasn't all that happy with the results, but, after I had sanded the surface around the new line, and used a bit of nose oil with my thumb to rub into the sanded surface, it came out ok. At a glance, who's gonna know?
Still more work than I had intended to do. Getting that preamp out of the cabinet was a PITA, since the bulk of the mounting screws are along the back flange on the roof of the cabinet, so either remove the power amp chassis, or remove the power tubes, and curse when you can't get anything but a right-angle ratcheting Philips screwdriver in where the two xfmrs disallow any size of normal scrrewdriver to remove those two. The front screws are right above the front side-wall cleats. No service loop on the bass control, which was the pot whose shaft broke. All in a days work.
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