I've been using vintage Christmas light strings for years, including cone-shaped C6 series strings on our two feather trees. I operate them at reduced voltage (66% for C6 and 75% for C7/C9) to greatly extend their livespans. I switched to vintage lamps years ago because I was dismayed at how easily the color scrapes off modern ones, and C6 lamps haven't been made since 1974. Most of my C7 and C9 lamps have inside color. In the past 20-odd years I've accumulated over 500 spare lamps. I replace only about 1 of each size per year, so my stash will way outlive me! Another benefit of running them below rated voltage is that they run MUCH cooler - cool enough that I can hold onto the C6 lamps indefinitely. There's way less fire hazard.

The image is of our smaller, 4' feather tree in our front window. Sorry the lamp colors don't render better - they're very vivid and different in person. When I was a kid my family didn't have C6 strings, but I saw them here and there and always liked their look. I think they're perfect on feather trees, even though our strings don't have the metal clips to hold the lamps upright. Trivia: those clips were invented because long ago, it was generally thought that running them in any position other than base down shortened their lifespan. That proved to be false. All our candelabras are vintage C7, 3-lamp types. We use C9s outdoors, including the more scarce C9 flame lamps around our front door. I even have 3 rare canary yellow G10 lamps, with 1 of them in the string around our garage door. Ours is the only house in the area with vintage (or even vintage-style) lighting. It just looks right in/on our 1947 stone house.

Oh by the way, we also have vintage blow-molded lighted "candles" on our front stoop to complete the look.

Joel