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Ampeg SVT Classic Vintage control knob issues

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  • Ampeg SVT Classic Vintage control knob issues

    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?

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    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.
    Logic is an organized way of going wrong with confidence

  • #2
    Extra points for mentioning the use of nose oil. I call it nose grease. Great stuff innit? Absolutely indispensible.

    Old style SVT's, heck I just disassemble the whole thing if I have to get into the preamp. It's all such a big PITA innit? Beats scraping up hands & wrists trying to loosen the preamp mounting screws. There's no good shortcuts.
    This isn't the future I signed up for.

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    • #3
      Originally posted by Leo_Gnardo View Post
      Extra points for mentioning the use of nose oil. I call it nose grease. Great stuff innit? Absolutely indispensible.
      I got that trick when I had taken an oboe I had bought years ago that was claimed to be a Loree (but didn't look right) to RDG Woodwinds (formerly Robert Gilberts woodwinds) shop in LA, and while their seasoned repair man was looking for hidden details in the wood, he reached up with a finger and extracted a bit of nose oil and rubbed it into the surface to bring out the faint engraved numbers in the wood. Turned out to be a fake. YUP.....nose grease....indeed great stuff!
      Logic is an organized way of going wrong with confidence

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      • #4
        I'm laughing. When my wife says, "do you have any Chapstick?" I say, "Here, kiss my forehead."
        --
        I build and repair guitar amps
        http://amps.monkeymatic.com

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        • #5
          Wonderful amp, very well built, better than 70s but nothing beats MTI's from early 80s.
          Just the squared look...

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          • #6
            When I was young, an old timer showed me the nose oil trick on the parts where a fishing rod fits together.
            It's weird, because it WAS working fine.....

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